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OCR Categories Archives: Module 6: Genetics, Evolution and Ecosystems

Cellular Control

Cellular Control

  • state that genes code for polypeptides including enzymes

Gene – a length of DNA that codes for one or more polypeptides, including enzymes.

Polypeptide – a polymer consisting of a chain of amino acids residues joined by peptide bonds.

Protein – a large polypeptide – usually 100 or more amino acids. Some proteins consist of one polypeptide chain and some consist of more than one polypeptide chain.

Genome – the entire DNA sequence of that organism. The human genome consists of about 3 billion nucleotide base pairs.

 

 

 

  • explain the meaning of the term genetic code

Genetic Code – the sequence of nucleotide bases on a gene that provides the codes for the construction of a polypeptide of a protein. The characteristics of the genetic code includes:

  • Triplet code – a sequence of three nucleotide bases codes an amino acid.
  • Degenerate code – all amino acids (except methionine) have more than one code.
  • Stop codes – indicates the end of a polypeptide chain (doesn’t correspond to an amino acid).
  • Widespread but not universal – where the same base sequence codes for similar polypeptides in different organisms, but are not always identical

 

 

  • describe, with the aid of diagrams, the way in which a nucleotide sequence codes for the amino acid sequence in a polypeptide

Transcription – the creation of a single-stranded mRNA copy of the DNA coding strand.

Messenger RNA (mRNA)activated nucleotides that uses complementary base pairing to the template strand to be arranged identically to the coding strand, other than uracil being present and thymine being absent. They carry the codons that are used to be make the polypeptide.

 

 

  1. The gene unwinds and unzips, by the length of the DNA that makes up the gene dips into the nucleolus. The hydrogen bonds between the complementary bases break forming two
  • Template strand – the strand of DNA that is used to help make mRNA. RNA nucleotides use the template strand to make mRNA through complementary base pairing between the template strand and mRNA.
  • Coding strand – the strand of DNA that is identical to mRNA, other than the base uracil being present in preference to thymine.
  1. Activated RNA nucleotides bind, using hydrogen bonds, to the exposed bases on the template strand, through complementary base pairing (U binds with A, C binds with G), catalysed by the enzyme RNA polymerase.
  2. Two extra phosphoryl groups are released, which releases energy for bonding adjacent nucleotides.
  3. mRNA is formed and passes out of the nucleus through a pore in the nuclear envelope, to a ribosome.
  • describe, with the aid of diagrams, how the sequence of nucleotides within a gene is used to construct a polypeptide, including the roles of messenger RNA, transfer RNA and ribosomes

Translation – the assembly of polypeptides (proteins) at ribosomes.

Transfer RNA (tRNA)lengths of RNA that fold into hairpin shapes and have three exposed bases at one end where a particular amino acid can bind. At the other end of the molecule are three unpaired nucleotide bases, known as an anticodon.

 

 

  1. mRNA binds to a ribosome. Two codons are attached to the small subunit of the ribosome. The first codon is always AUG, which codes for methionine. A tRNA with methionine and the anticodon UAC forms hydrogen bonds with this codon.
  2. The next tRNA, with another amino acid, binds to the second exposed codon on the mRNA with its complementary anticodon.
  3. A peptide bond forms between the two adjacent amino acids. This repeats forming a polypeptide.
  4. The last codon on the mRNA is called the stop codon (UAA, UAC or UGA), which stops translation.
  5. The rough endoplasmic reticulum packages the polypeptide into a vesicle, which moves to the Golgi apparatus to give the protein its final secondary/tertiary structures.

 

  • state that mutations cause changes to the sequence of nucleotides in DNA molecules

Mutation – a change in the amount of or arrangement of the genetic material in a cell, by base deletion, addition, substitution or by inversion or repeat of a triplet. Mutations cause changes to the sequence of nucleotides in DNA molecules.

 

Mutations may occur during DNA replication. Certain substances (mutagens) may cause mutations, including tar found in tobacco, UV light, X-rays and gamma rays. Mitotic mutations are somatic mutations and are not passed on to offspring. Meiotic mutations and gamete formation can be inherited (passed on to offspring).

 

What types of mutation are there?

  1. Insertion/deletion mutations – in which one of more nucleotide pairs are inserted or deleted from a length of DNA, causing a frameshift – the amino acid sequence is altered after the insertion/deletion point.
  2. Point mutations/Substitution – in which one base pair replaces
  • Nonsense – introduces a premature stop codon, stopping translation early, giving a truncated
  • Missense – changes the codon, changing the amino acid produced, so there is a change in the tertiary structure.
  • Silent – changes the codon, but the amino acid produced is not changed, so the amino acid sequence remains the same.

  • explain how mutations can have beneficial neutral or harmful effects on the way a protein functions

 

 

Allele – an alternative version of a gene. It is still at the same locus on the chromosome and codes for the same polypeptide but the alteration to the DNA base sequence may alter the protein’s structure.

Mutations with Neutral Effects:

If a gene is altered by a change to its base sequence, it becomes another version of the same gene – an allele. It may produce no change to the organism if:

  • The mutation is in a non-coding region of the DNA.
  • It is a silent mutation – the base triplet changes but still codes for the same amino acid, so the protein is unchanged.

If a mutation does cause a change to the structure of the protein, and therefore different characteristics, but the changed characteristic gives no particular advantage or disadvantage to the organism, then the effect is also neutral.

Mutations with Harmful or Beneficial Effects:

Early humans in Africa almost certainly had dark skin. The pigment melanin protected from the harmful effects of ultraviolet light. However, they could still synthesise vitamin D from the action of the intense sunlight on their skin. This is an important source of vitamin D, because much of the food that humans eat contains very little vitamin D.

The Inuit people have not lost all their skin pigments, although they do not live in an environment that has intense sunlight. However, they eat a lot of fish and seal meat, including the blubber, both rich sources of dietary vitamin D. Depending on the environment, the same mutation for paler skin can be beneficial or harmful. Individuals within a population who have a certain characteristic may be better adapted to the new environment. The well-adapted organisms can out-compete those in the population that do not have the advantageous characteristics. This is natural selection, the mechanism for evolution. Without genetic mutations there would be not evolution.

 

  • state that cyclic AMP activates proteins by altering their three-dimensional structure

Some proteins have to be activated by a chemical, cyclic AMP that, like ATP, is a nucleotide derivative. Cyclic AMP activates proteins by altering their three-dimension structure, so that their shape is a better fit to their complementary molecules.

 

  • explain genetic control of protein production in a prokaryote using the lac operon
  1. coli normally respires glucose but it can also use lactose as a respiratory substrate. E. coli grown in a culture medium with no lactose can be placed in a medium with lactose. At first they cannot metabolise the lactose because they only have tiny amounts of the two enzymes needed to metabolise it. A few minutes after lactose is added to the culture medium, E. coli bacteria increases the rate of synthesis if the enzymes by about 1000 times. Lactose must trigger the production of the two enzymes, and is known as the inducer.

 

The lac operon is a section of DNA within the bacterium’s DNA, consisting of:

  • Structural genes – the enzymes:
  • β-galactosidase – breaks down lactose to glucose and galactose.
  • Lactose permease – helps the cell to absorb lactose/increase uptake of lactose.
  • Control sites:
  • Operator region – binds to the repressor and can switch on and off the structural genes.
  • Promoter region – binds to RNA polymerase and controls transcription.

 

The regulator gene controls the production of repressor protein. This repressor molecule binds to the operator region, preventing RNA polymerase binding to the promoter region and preventing transcription. Therefore the structural genes are switched off and lactose is not broken down.

  • explain that the genes that control the development of the body plans are similar in plants, animals and fungi, with reference to homeobox sequence

Homeobox genesregulatory genes that codes for proteins that controls the development of body plans.

 

Homeobox genes each contain a sequence of 180 base pairs (homeobox) coding for the homeodomain. The homeodomain on the protein is able to bind to DNA, switching it on or off controlling transcription (the protein is the transcription factor). Homeobox genes are arranged into clusters known as Hox clusters. Some organisms have more Hox clusters than others.

Homeobox genes genetically mediate development of organisms:

  • Maternal-effect genes – determine the embryo’s polarity (which end is the head (anterior) and which end is tail (posterior)).
  • Segmentation genes – specify the polarity of each segment.
  • Homeotic selector genes – specifies the identity of each segment and direct the development of individual body segments. These are the master genes in the control networks of regulatory genes. There are two gene families:
  • The complex that regulates development of thorax and abdomen
  • The complex that regulates development of head and thorax

Mutations of these genes can change one body part to another. This can be seen in the condition known as antennapedia – where the antennae of Drosophila look more like legs.

 

  • outline how apoptosis (programmed cell death) can act as a mechanism to change body plans

Apoptosisprogrammed cell death that occurs in multicellular organisms. Cells should undergo about 50 mitotic divisions (the Hayflick constant) and then undergo a series of biochemical events that leads to an orderly and tidy cell death. This is in contrast to cell necrosis, an untidy and damaging cell death that occurs after trauma and releases hydrolytic enzymes. The apoptosis process occurs very quickly.

  1. Enzymes break down the cell cytoskeleton.
  2. The cytoplasm becomes dense, with organelles tightly packed.
  3. The cell surface membrane changes and small bits called blebs
  4. Chromatin condenses and the nuclear envelope breaks. DNA breaks into fragments.
  5. The cell breaks into vesicles that are taken by phagocytosis. The cellular debris is disposed of and does not damage any other cells or tissues.

 

Apoptosis is controlled by a diverse range of cell signals, including cytokines made by cells of the immune system, hormones, growth factors and nitric oxide. Nitric oxide can induce apoptosis by making the inner mitochondrial membrane more permeable to hydrogen ions and dissipating the proton gradient. Protons are released into the cytosol. These proteins bind to apoptosis inhibitor proteins and allow the process to take place.

 

Apoptosis is an integral part of plant and animal tissue development. The excess cells shrink, fragment and are phagocytosed so that the components are reused and no harmful hydrolytic enzymes are released into the surrounded tissue. Apoptosis is tightly regulated during development, and different tissues use different signals for inducing it. It weeds out ineffective or harmful T lymphocytes during the development of the immune system.

During limb development apoptosis causes the digits (fingers and toes) to separate from each other.

 

Children between the ages of 8-14 years, 20-30 billion cells per day undergo apoptosis. In adults, 50-70 million cells per day undergo apoptosis. If the rates are not balanced:

  • Not enough apoptosis leads to the formation of tumours.
  • Too much apoptosis leads to cell loss and degeneration.

Cell signalling plays a crucial role in maintaining the right balance.

 

 

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Diet and Food Production

Diet and Food Production

 

  • define the term balanced diet

A balanced diet is a diet that contains appropriate amounts of all necessary nutrients required for healthy growth and activity. This includes:

  • Carbohydrates – for energy
  • Fats – for energy and insulation
  • Proteins – for growth and repair
  • Fibre – helps with the digestive system
  • Minerals/Vitamins – essential for body functions/chemical processes
  • Water – essential for body function and for transport

Health is about:

  • Having a good nutrition
  • Being free from disease
  • Having a good well-being (physical, mental and social)
  • Having suitable housing

 

  • explain how consumption of an unbalanced diet can lead to malnutrition with reference to obesity

Malnutrition is having a lack of proper nutrition, caused by not an unbalanced diet – not having enough to eat or not eating enough of the right things.

Obesity is when a person’s body weight is 20% or more than the recommended weight for their height. It’s caused by:

  • Eating too much
  • Doing sufficient exercise
  • Energy intake is more than energy use
  • Having an unbalanced diet consisting mostly of fats, sugars, carbohydrates and alcohol

Obesity is thought to be the most important dietary factor in the following health problems:

  • Cancer
  • Cardiovascular disease
  • Type 2 diabetes

You can measure whether a person is obese or not using their BMI (Body Mass Index):

Problems with BMI – why might someone be placed in the wrong health category based on BMI score?

  • There are differences between male and female:
  • Women have a higher percentage of body fat
  • A woman may be pregnant
  • BMI doesn’t measure actual fat
  • The person may have more/less muscle/bone than normal
  • Muscle/bone is heavier than fat
  • BMI is only for adults
  • discuss the possible links between diet and coronary heart disease

Coronary heart disease (CHD) is the result of atherosclerosis. Atherosclerosis is the deposition of fatty substances in the walls of coronary arteries. It narrows the size of the lumen restricting blood flow to the heart muscle, which may cause oxygen starvation.

The endothelium (inner lining) of the artery can become damaged. The damage is repaired by of white blood cells (phagocytes)encouraging the growth of smooth muscle and the deposition of fatty substances. The deposits (atheromas) include cholesterol from low-density lipoproteins (tiny balls of fat and protein that are used to transport cholesterol around in the blood), fibre, dead blood cells and platelets. The build-up of atheromas occurs under the endothelium, in the wall of the artery. It eventually forms a plaque, which sticks out into the lumen of the artery, leaving the artery wall rougher and less flexible as well as creating a narrower lumen, reducing blood flow.

  • discuss the possible effects of a high blood cholesterol level on the heart and circulatory system, with reference to high-density lipoproteins (HDL) and low-density lipoprotein (LDL)

Cholesterol is essential to the normal functioning of the body. They are found in cell membranes to improve stability and used to make steroid sex hormones and bile. Therefore cholesterol must be transported around the body, however it is not soluble in water so must first be converted to a form that will mix with water. It is therefore transported in the form of lipoproteins (tiny balls of fat combined with protein). There are two types of lipoprotein: high-density lipoproteins (HDL) and low-density lipoproteins (LDL). They are both released into the blood and can be taken up by cells that have the correct receptor sites.

We do not eat lipoproteins, but our diet has a significant effect on the lipoprotein concentration in our blood. LDLs are associated with greater deposition in the artery walls so is best to maintain a low proportion of LDLs. HDLs are associated with reduced deposition in the artery walls so is best maintain a high proportion of HDLs in our blood.

  • Eating saturated (animal) fats will increase the concentration of LDLs
  • Eating a low-fat diet will reduce the overall concentration of lipoproteins
  • Eating unsaturated fats increases the concentration of HDLs
  • Eating polyunsaturated fats reduces the concentration of LDLs
  • Eating monounsaturated fats reduces the concentration of LDLs
  • explain that humans depend on plants for food as they are the basis of all food chains
  • Plants start off all food chains. They carry out photosynthesis, where they convert light energy into chemical energy – absorb carbon dioxide from the air and make carbohydrates. They also absorb minerals, such as nitrates, from the soil and manufacture a range of other biological molecules
  • Herbivores make use of the biological molecules that the plants make when they eat and digest plants
  • Carnivores eat herbivores and the energy moves along the food chain
  • Humans are omnivores and eat a combination of plants and animals so we gain our energy both directly from plants and indirectly by eating animals.
  • outline how selective breeding is used to produce crop plants with high yields, disease resistance and pest resistance

Selective breeding involves selecting plants with good characteristics (e.g. high yields, disease resistance or pest resistance) to reproduce together in order to increase productivity.

  1. Select plants with good characteristics that will increase crop yield and breed them together
  2. Select offspring with the best characteristics and breed them together
  3. Continue this over several generations causing the required characteristic to become more exaggerated
  • outline how selective breeding is used to produce domestic animals with high productivity

Selective breeding can be used to increase the productivity of animals.

  1. Select animals with good characteristics that will increase meat yield, e.g. largest cows and bulls, and breed them together
  2. Select offspring with the best characteristics, e.g. largest, and breed them together

3. Continue those over several generations until cows with very high eat yields are produced, e.g. very large cows

 

  • describe how the use of fertilisers and pesticides with plants and the use of antibiotics with animals can increase food production

  • describe the advantages and disadvantages of using microorganisms to make food for human consumption

Microorganisms can spoil food in 4 ways:

  • Visible growth – colonies of Mucor and Penicillium can grow on food turning it either black or blue/green.
  • External digestion process – they release enzymes into the food and absorb the nutrients released by breakdown of the food molecules and the food eventually will be reduced to a mush.
  • Releasing Toxins – the bacterium Clostridium botulinum produces a toxin called botulin, causing botulism, which is very dangerous and harmful.
  • Infection – e.g. Salmonella bacteria can be present in poultry products and attack the lining of the stomach and digestive system

 

Microorganisms have been used for many years in the manufacture of food and drinks. Examples include:

  • outline how salting, adding sugar, pickling, freezing, heat treatment and irradiation can be used to prevent food spoilage by microorganisms

 

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Ecosystems

Ecosystems

 

  • define the term ecosystem

Ecosystem – all living organisms and non-living components in a specific habitat, and the interrelationships between them.

Habitat – the place where an organism lives.

Population – all of the organisms of one species , who live in the same place at the same time, and can breed together.

Community – all the organisms of different species, who live in the same place at the same time, and can interact with each other.

Niche – the role that each species plays in an ecosystem.

Autotroph – an organism that uses light energy to synthesise its own complex organic molecules.

Heterotroph – an organism that consumes complex organic molecules to gain nutrients, obtaining energy.

  • state that ecosystems are dynamic systems

Ecosystems are dynamic systems because the population rises and falls due to the interactions of living organisms between each other and with the physical environment. Any small changes in one thing can affect the others. For example, if a predator’s population size goes up, the population size of the prey will go down.

  • define the term biotic factor and abiotic factor, using named examples

Biotic factors – the effects of living organisms, e.g. food supply, predation, disease, competition.

Abiotic factors– the effects of non-living components, e.g. temperature, pH of soil, soil type, light intensity, oxygen concentrations, carbon dioxide concentrations.

  • define the term producer, consumer, decomposer and trophic levels

  • describe how energy is transferred through ecosystems

Food chains show how energy is transferred from one organism to another. Different food chains join together to make a food web, which helps us understand how energy flows through the whole ecosystem. The arrows in a food chain show the direction of energy transfer.

  • discuss the efficiency of energy transfers between trophic levels

Energy is lost at each trophic level and is unavailable to the next trophic level. Energy is used for respiration which is lost through heatenergy. The energy is stored in dead organisms and waste material which can only be accessed by decomposers. Because of this, there is less living tissue (biomass) at higher levels of a food chain. There are always less consumers as the pyramid gets higher due to energy loss at each trophic level.

  • outline how energy transfers between trophic levels can be measured

 

  • explain how human activities can manipulate the flow of energy through ecosystems

  • describe one example of primary succession resulting in a climax community

Succession – a change in a habitat causing a change in the make-up of a community.

Succession on Sand Dunes:

  1. Pioneer plants like sea rocket(Cakilemaritima)and prickly sandwort (Salsola kali) colonise the sand just above the high water mark – tolerate salt water, lack of freshwater and unstable sand.
  2. Wind-blown sand builds up around the base of these plants, forming a ‘mini’ sand dune. As plants die and decay, nutrients accumulate in this mini sand dune. As the dune gets bigger, plants like sea sandwort(Honkenyapeploides) and sea couch grass(Agropyronjunceiforme) colonise it, which have long roots to stabilise it in the sand.
  3. With more stability and accumulation of more nutrients, plants like sea spurge(Euphorbaparalias) and marram grass(Ammophilaarenaria)start to grow. Marram grass traps sand, as the sand accumulates, the shoots grow taller to stay above the growing dune trapping more sand.
  4. As the sand dune and nutrients build up, other plants colonise the sand, such as hare’s foot clover(Trifoliumarvense)and bird’s foottrefoil(Lotuscorniculatus). These have bacteria in their root nodules to convert nitrogen into nitrates. With nitrates available, more species like sand fescue(Festucarubra) and viper’sbugloss(Echiumvulgare) colonise the dunes, stabilising the dunes further.

  • describe how the distribution and abundance of organisms can be measured, using line transects, belt transects, quadrats and point quadrats

A transect is a line taken across a habitat. You stretch a tape measure across the habitat and take samples along the line.  You can use a:

  • Line Transect – recording each organism which is touching the line at suitable, regular intervals.
  • Belt Transect – placing a quadrat against the line, recording its contents, then placing the next quadrat immediately touching the first one, repeating this along the transect.
  • Interrupted Belt Transect – placing quadrats at regular intervals along the transect.

 

Abundant80-100%
Common60-80%
Frequent40-60%
Occasional20-40%
Rare0-20%

A quadrat is a square frame used to define the size of the sample area. It’s important to choose the right size of the quadrat (normally 50cm or 1m quadrats are used) depending on the size of the area. The quadrat is placed randomly and the abundance is measures. You could:

  • Count the number of individuals of each species.
  • Estimate the percentage cover of each species – this is the proportion of the area within the quadrat which it occupies.
  • Use an abundance scale, such as the ACFOR scale, by estimating which one of these best describes the abundance of each species within the quadrat.

A point quadrat may be used. This is a frame holding a number of long needles or pointers. You lower the frame into the quadrat and record any plant touching the needles. It can also be useful for measuring the height of plants.

Population size = mean no. of individuals of the species in each quadrat

fraction of the total habitat are covered by a quadrat

It’s important to decide where to place the quadrats, how many samples to take, and how big they should be:

  • Use a sample which is representative of the whole habitat: randomly position the quadrats across the habitats, using random numbers to plot coordinates or take samples at regular distances across the habitat.
  • To work out how many quadrats are needed: do a pilot study – take random samples from across the habitat and make a cumulative frequency table. Plot cumulative frequency against quadrat number. The point where the curve levels off tells them that the minimum number of quadrats to use. Ecologists often double
  • To work out how big your quadrats should be: count the number of species you find in larger quadrats. Plot quadrat area on the x-axis, against the number of species you find in each one on the y-axis. Read the optimalquadrat size at the point where he curve starts to level off.
  • describe the role of decomposers in the decomposition of organic material

Decomposers, such as bacteria and fungi, break down dead and waste organic material. Bacteria and fungi feed saprotrophically so are called saprophytes. They secrete enzymes onto dead and waste material. The enzymes digest the material into small molecules, which are then absorbed into the organisms body. Having been absorbed, the molecules are stored or respired to release energy.

If bacteria and fungi did not break down dead organisms then energy and valuable nutrients would remain trapped in the dead organisms. Microbes get a supply of energy to stay alive, and the trapped nutrients are recycled.

  • describe how microorganisms recycle nitrogen within ecosystems (Only Nitrosomonas, Nitrobacter and Rhizobium need to be identified by name)

Nitrogen gas is very unreactive, so is impossible for plants to use it directly. Nitrogen is needed to make proteins and nucleic acids. Plants need fixed nitrogen as ammonium ions (NH4+) or nitrate ions (NO3). Bacteria is involved in the recycling of nitrogen.

Nitrogen Fixation:

  • Nitrogen fixation can occur when lightning strikes or through the Haber process – only 10% of total nitrogen fixation.
  • Nitrogen-fixing bacteria live freely in the soil and fix nitrogen using it to make amino acids. Nitrogen-fixing bacteria, such as Rhizobium, also live inside the root nodules of legumes (bean plants).
  • They have a mutualistic relationship with the plant, fixing nitrogen and receiving carbon compounds such as glucose in return.
  • Proteins, such as leghaemoglobin, in the nodules absorb oxygen to keep the conditions anaerobic. Under these conditions, the bacteria use nitrogen reductase to reduce nitrogen gas to ammonium ions (NH4+) that can then be used by the host plant.

Nitrification:

  • Nitrification happens when chemoautotrophic bacteria in the soil absorb ammonium ions.
  • Ammonium ions (NH4+) are released by bacteria involved in putrefaction of proteins found in dead or waste organic matter.
  • Chemoautotrophic bacteria obtains energy by oxidising ammonium ions (NH4+) to nitrites (NO2) (Nitrosomonas bacteria), or by oxidising nitrites (NO2) to nitrates (NO3) (Nitrobacter bacteria).
  • As oxidation requires oxygen, these reactions only happen in well-aerated soils.
  • Plants need nitrates to make amino acids, proteins, enzymes, DNA, RNA, etc.

Denitrification:

  • Other bacteria convert nitrates back to nitrogen gas.
  • When the bacteria grows under anaerobic conditions, such as waterlogged soils, they use nitrates (NO3) as a source of oxygen for their respiration and produce nitrogen gas (N2) and nitrous oxide (N2O).

 

 

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Biotechnology

Biotechnology

  • state that biotechnology is the industrial use of living organisms (or parts of living organisms) to produce food, drugs or other products

Biotechnology – the industrial use of living organisms (or parts of living organisms) to produce food, drugs or other products.

  • explain why microorganisms are often used in biotechnological processes

Many biotechnological processes make use of microorganisms (bacteria and fungi) as they have many advantages:

  • Rapid growth in favourable conditions.
  • Proteins and chemicals produced can be harvested.
  • Can be genetically engineered to produce specific products.
  • Grows well at low temperatures – lower than those chemical processes.
  • Can be grown anywherenot climate-dependent.
  • Purer products than those produced in chemical processes.
  • Can be grown using nutrient materials that are useless or toxic to humans.

  • describe, with the aid of diagrams, and explain the standard growth curve of a microorganism in a closed culture

A culture is a growth of microorganisms. A pure culture contains one microorganism and a mixed culture contains multiple species.

  1. Lag phase – organisms are adjusting to surroundings (taking in water, cell expansion, activating specific genes, synthesising specific enzymes. Cells are active but not reproductive = population remains fairly constant.
  2. Log (exponential) phase – population size doubles each generation as every individual has enough space and nutrients to reproduce.
  3. Stationary phase – nutrient levels decrease and waste products and other metabolites build up. Rate of death is equal to rate of reproduction.
  4. Decline/death phase – nutrient exhaustion and increased levels of waste products and metabolites lead to death rate exceeding reproduction rate. Eventually, all organisms will die in a closed system.
  • describe how enzymes can be immobilised

Immobilisation of enzymes – where enzymes are held, separated from the reaction mixture. Substrate molecules can bind to the enzyme molecules and the products formed go back into the reaction mixture leaving the enzyme molecules in place.

Methods for immobilising enzymes depend on ease of preparation, cost, relative importance of enzyme ‘leakage’ and efficiency of the particular enzyme that is immobilised.

  • explain why immobilised enzymes are used in large-scale production

In many areas of clinical research and diagnosis and in some industrial processes, the product of a single chemical reaction is required. It is often more efficient to use isolated enzymes to carry out the reaction rather than growing the whole organism or using an inorganic catalyst. Isolated enzymes can be produced in large quantities in commercial biotechnological processes.

Downstream processing – the extraction of enzyme from the fermentation mixture, involving separation and purification of any product of large-scale fermentations.

  • compare and contrast the processes of continuous culture and batch culture

Industrial-scale fermentations can be operated in two ways:

  • Batch:
  • The microorganism is mixed with a specific quantity of nutrient solution.
  • It is left to grow for a fixed period with no further nutrient added.
  • At the end of the period, the products are removed and the fermentation tank is emptied.
  • For example, pencillin.
  • Continuous:
  • Nutrients are added to the fermentation tank.
  • Products are removed from the fermentation tank at regular intervals/continuously.
  • For example, insulin.

  • describe the differences between primary and secondary metabolites

Metabolites – the products of metabolism (the sum of all of the chemical reactions in an organism), e.g. new cells and cellular components, chemicals such as hormones and enzymes, waste products such as carbon dioxide, oxygen, urea, ammonia, nitrates.

Primary metabolites – substances produced by an organism as part of its normal growth, e.g. amino acids, proteins, enzymes, nucleic acids, ethanol, lactate. The production of primary metabolites matches the growth in population of the organism.

Secondary metabolites – substances produced by an organism that are not part of its normal growth, e.g. antibiotic chemicals. The production of secondary metabolites usually begins after the main growth period of the organisms – does not match the growth in population of the organism.

  • explain the importance of manipulating the growing conditions in a fermentation vessel in order to maximise the yield of product required

Commercial applications of biotechnology often require the growth of a particular organism on an enormous scale. An industrial-scale fermenter is essentially a huge tank, which may have capacity of tens of thousands of litres. The growing conditions in it can be manipulated and controlled in order to ensure the best possible yield of the product.

The conditions that affect the microorganisms being cultured include:

  • explain the importance of asepsis in the manipulation of microorganisms

Asepsis – the absence of unwanted microorganisms.

Aseptic technique – refers to the measures to ensure that unwanted microorganisms do not contaminate the culture that is being grown or the products that are extracted.

The nutrient medium in which the microorganisms grow could also support the growth of many unwanted microorganisms. Any unwanted microorganism is called a contaminant. Unwanted microorganisms:

  • Compete with the culture microorganisms for nutrients and space.
  • Reduce the yield of useful products from the culture microorganisms.
  • May cause spoilage of the product.
  • May produce toxic chemicals.
  • May destroy the culture microorganism and their

 

 

 

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Populations and Sustainability

Populations and Sustainability

(a) explain the significance of limiting factors in determining the final size of a population

Population size is a balance between death rate and rate of reproduction. A habitat cannot support a population larger than its carrying capacity because of the limiting factors, which place a limit on population size. The limiting factors may include food, water, light, oxygen, shelter, predators,parasites, intensity of competition within and between species etc.

(b) explain the meaning of the term carrying capacity

(c) describe predator-prey relationships and their possible effects on the population sizes of both the predator and the prey

Predators are animals that hunt other animals (prey). Predation can act as a limiting factor on a prey’s population size.

  1. More predators = more prey eaten.
  2. Prey population decreases = less food for predators.
  3. Fewer predators survive = predator population decreases.
  4. Fewer prey now eaten = prey population increases.
  5. More prey = predator numbers increase and the cycle begins again.

(d) explain, with examples, the terms interspecific and intraspecific competition

Competition occurs when resources(like food or water) are not present in adequate amounts to satisfy the needs of all the individuals who depend on those resources. As the intensity of competition increases, the rate ofreproduction decreases (fewer organisms have enough organisms to reproduce), whilst the death rate increases (fewer organisms have enough resource to survive). There are two types of competition:

  • Intraspecific competition- competition between individuals of the same species for the same resources, e.g. male deer locking horns when competing for mates.
  • Interspecific competition- competition between individuals of different species for the same resources, e.g. cheetahs and lions competing for the same prey.

In 1934, GeorgyiFrantsevitchGause grew two species of Paramecium, both separately and together. When together, there was competition for food, with Paramecium aurelia obtaining more food effectively than Parameciumcaudatum, resulting in Paramecium caudatum dying out and the numbers for Paramecium aurelia increasing, eventually becoming the only species remaining.

Gause concluded that more overlap between two species’ niches would result in more intense competition. If two species have exactly the same niche, one would be out-competed by the other and would die out or become extinct in that habitat – competitive exclusion principle – used to explain why particular species only grow in particular places.

However, other observations and experiments suggest that extinction is not necessarily certainly going to happen:

  • Interspecific competition could result in one population being smaller than the other, with both population sizes remaining relatively constant.
  • Important to realise that in the laboratory, it’s easy to exclude the effects of other variables, so the habitat of the two species remains very stable. In the wild, however, a wide range of variablesmay act as limitingfactors for the growth of different populations – variables may change on a daily basis or even over the course of a year. For example, experiments on competition between flour beetles Triboliumconfusum and Triboliumcastaneum initially confirmed the competitive exclusion principle – the castaneum population size increased, whilst T. confusum died out – but even a small change in thetemperature could change the outcome so that T. confusum survived instead.

(e) distinguish between the terms conservation and preservation

(g) explain that conservation is a dynamic process involving management and reclamation

Conservation is the maintenance of biodiversity, including diversity between species, genetic diversity withinspecies, and maintenance of a variety of habitats and ecosystems.Conservation is a dynamic process involving management and reclamation.

Unfortunately, a steadily increasing human population can threaten biodiversity through:

  • Over-exploitation of wild populations for food (e.g. cod in the North Sea), for sport (e.g. sharks) and for commerce (e.g. pearls collected from saltwater oysters and freshwater clams): species are harvestedfaster than they can replenish
  • Habitat destruction and fragmentation as a result of more intensive agricultural practices, increased pollution, or widespread building.
  • Introduction of species to an ecosystem by humans, deliberately or accidentally. These may out-compete native species, which may become extinct.

Conservation can involve establishing protected areas such as National Parks or Sites of Special Scientific Interest. It can also involve giving legal protection to endangered species, or conserving them ex-situ in zoos or botanic gardens. However, maintaining biodiversity in dynamic ecosystems requires careful management.

Some management strategies include:

  • Raise carrying capacity by providing more food.
  • Move individuals to enlarge populations.
  • Fencing to restrict dispersal of individuals.
  • Control predation and poachers.
  • Vaccinate individuals against disease.
  • Preserve habitats by preventing pollution/disruption, or intervene to restrict the progress of succession, e.g. coppicing, mowing, grazing.

Preservation is the protection of ecosystems, as yet unused by humans, leaving it untouched so it is kept exactly as it is.

(f) explain how the management of an ecosystem can provide resources in a sustainable way, with reference to timber production in a temperate country

With human population getting larger and expanding exponentially, it is putting pressure on our resources. More intensive methods need to be used to exploit our environment for resources, however such methods can disrupt or destroy ecosystems, reduce biodiversity or deplete resources. One situation is the potential conflict between our need for resources and conservation is in wood and timber production.

(h) discuss the economic, social and ethical reasons for conservation of biological resources

(i) outline, with examples, the effects of human activities on the animal and plant populations in the Galapagos Islands

 

 

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Genomes and Gene Technologies

Genomes and Gene Technologies

  • outline the steps involved in sequencing the genome of an organism

Genome – all the genetic information within an organism OR all the genetic information within an individual.

Genome sequencing – the technique used to give the base sequence of DNA of a particular organism.

  1. Genomes are mapped to identify which part of the genome they have come from.
  2. Samples of the genome are sheared (mechanically broken) into smaller sections of around 100,000 base pairs.
  3. These sections are placed into separate bacterial artificial chromosomes (BACs) and transferred to coli cells. As these cells grow in culture, many clones of the sections are produced – clone libraries.
  4. PCR: DNA is extracted from BACs and replicated. Different restriction enzymes are used to cut the DNA into smaller overlapping fragments.
  5. Electrophoresis: The fragments are separated into size order. Computer programmes are used to reassemble the full BAC sequence by analysing the overlaps shown by the fragment sequences.

Automated DNA Sequencing Based on Interrupted PCR and Electrophoresis:

Sequencing DNA fragments was initially slow using radioactively labelled nucleotides. The development of automated sequencing has led to a rapid increase in the number of organism genomes sequenced and published in recent years.

  1. The primer joins (anneals) at the 5’ end, allowing DNA polymerase to attach.
  2. DNA polymerase adds free nucleotides by complementary base pairing the strand extends (PCR).
  3. If a modified nucleotide is added, the DNA polymerase enzyme is ‘thrown off’ and replication stops at that point. The nucleotide is modified by adding different coloured fluorescent markers to different bases.
  4. This process is repeated and many different sized DNA strands are created due to the random joining of modified nucleotides. Some may only have one additional nucleotide added to the primer, others may have more.
  5. The different sized DNA strands run through the machine (electrophoresis) sorting them from smallest length first to the longest A laser reads the colour sequence of the modified nucleotide on the end of each DNA strand, displaying the sequence of bases formed. Complementary base pairing of this sequence will tell you the base sequence on the original DNA strand.
  • outline how gene sequencing allows for genome-wide comparisons between individuals and between species

Genomics – the study of the whole set of genetic information in the form of the DNA base sequences that occur in the cells of organisms of a particular species.

Comparative gene mapping – knowing the sequence of bases in a gene of one organism and being able to compare genes for the same (or similar) proteins across a range of organisms.

The DNA of all organisms contains sections known as genes which code for the production of polypeptides and proteins. However, this coding DNA is only 1.5% of the genome of humans. Much DNA is non-coding DNA and has been referred to as junk DNA, which is misleading as this non-coding DNA carries out a number of regulatory functions. Genomics is seeking to map the whole genome of an increasing number of organisms. Comparing genes and regulatory sequences of different organisms will help us to understand the role of genetic information in a range of areas including health, behaviour and evolutionary relationships between organisms.

Comparative gene mapping has a wide range of applications:

  • The identification of genes for proteins found in all/many living organisms shows the importance of these in life.
  • Comparing DNA/genes of different species shows evolutionary relationships. The more DNA sequences organisms share, the more closely related they are likely to be.
  • Modelling the effects of changes to DNA/genes can be carried out, e.g. testing the effects of mutations on genes obtained from yeast that are also found in the human genome.
  • Comparing genomes from pathogenic and similar but non-pathogenic organisms can be used to identify the genes that are most important in causing the disease, leading to the identification of targets for developing more effective drug treatments and vaccines.
  • The DNA of individuals can be analysed – reveal mutant alleles, or the presence of alleles associated with increased risk of particular diseases, e.g. heart attack or cancer.
  • define the term recombinant DNA

Recombinant DNA – the resulting DNA formed from DNA fragments from different organisms joined using restriction enzymes and ligase enzymes.

  • explain that genetic engineering involves the extraction of genes from one organism, or the manufacture of genes, in order to place them in another organism (often of a different species) such that the receiving organism expresses the gene product

The two main reasons for carrying out genetic engineering are:

  • Improving a feature of the recipient organism – e.g. herbicide resistance, growth-controlling genes.
  • Engineering organisms that can synthesise useful products – e.g. hormone genes (insulin, growth hormones), Golden RiceTM (beta-carotene production) and pharmaceutical chemicals (inserting genes into sheep so that they produce chemical products that can be easily collected from their milk.

There are 4 steps of genetic engineering:

  1. Obtain the required gene.
  • mRNA is used as a template strand to make a copy of the gene using reverse transcriptase.
  • Use an automated polynucleotide sequencer to synthesise the gene.
  • Use a DNA probe to locate the gene on DNA fragments and cut using restriction enzymes.
  1. Place a copy of a gene in a vector.
  • Gene is sealed into a bacterial plasmid using DNA ligase, or the gene is sealed into virus genomes or yeast cell chromosomes.
  1. The vector carries the gene to the recipient cell.

The gene, one packaged in a vector, can form quite a large molecule that does not easily cross the membrane to enter the recipient cell. Methods used to get the vector into the recipient cell include:

  • Electroporationhigh-voltage pulse disrupts the membrane.
  • Microinjection – DNA injected using a micropipette into the host cell’s nucleus.
  • Viral Transfer – uses the virus’ mechanism for infecting cells by inserting DNA directly.
  • Ti Plasmids (vectors) inserted into soil bacterium Agrobacterium tumefaciens – plants are infected with bacterium, inserting the DNA plasmid into the plant’s genome.
  • Liposomes (DNA wrapped in lipid molecules) – fat-soluble and can cross the lipid membrane by diffusion.
  1. The recipient cell expresses the gene through protein synthesis.
  • describe how sections of DNA containing a desired gene can be extracted from a donor organism using restriction enzymes

Enzymes known as restriction enzymes (restriction endonucleases) are used to cut through DNA at specific points. A particular restriction enzyme will cut DNA wherever a specific base sequence occurs called the restriction site (usually less than 10 base pairs long). The enzyme catalyses the hydrolysis reaction that breaks the sugar-phosphate backbones of the DNA double helix. This gives a ‘staggered cut’, which leaves some exposed bases known as sticky ends.

  • outline how DNA fragments can be separated by size using electrophoresis

Electrophoresis – used to separate DNA fragments based on their size. This method relies on the substances within the mixture having a charge. When a current is applied, charged molecules are attracted to the oppositely charged electrode. The smallest molecules travel fastest through the stationary phase (a gel-based medium) and in a fixed period of time will travel furthest, so the molecules separate out by size.

  • describe how DNA probes can be used to identify fragments containing specific sequences

DNA probe – a short single-stranded piece of DNA (around 50-80 nucleotides long) that is complementary to a section of the DNA being investigated.

The probe is labelled one of two ways by attaching to the phosphate on nucleotides:

  1. Radioactive marker – the location can be revealed by exposure to photographic film.
  2. Fluorescent marker – emits a colour on exposure to UV light.

Different bases will have different coloured markers so that they can be distinguished.

  • outline how the polymerase chain reaction (PCR) can be used to make multiple copies of DNA fragments

The polymerase chain reaction is basically artificial DNA replication. It can be carried out on tiny samples of DNA in order to generate multiple copies of the sample. The differences between PCR and natural DNA replication include it can only replicate relatively short sequences of DNA (not entire chromosomes), the addition of a primer molecules (to start the process) and PCR involves a cycle of heating and cooling to separate and bind strands.

Primers – short, single stranded sequences of known bases (around 10-20 bases in length), that are the ‘starting point’ for DNA polymerase to bind – DNA polymerase enzymes cannot bind directly to single-stranded DNA.

The DNA polymerase enzyme is described as ‘thermophilic’ because it is not denatured by the extreme temperatures used in the process. The enzyme is derived from a thermophilic bacterium, Thermus aquaticus (Taq), which grows in hot springs at a temperature of 90oC.

  • explain how isolated DNA fragments can be placed in plasmids, with reference to the role of ligase

To join isolated fragments of DNA, an enzyme known as DNA ligase catalyses the condensation reaction that joins the sugar-phosphate backbones of the DNA double helix together. In order to join together DNA fragments from different sources, both fragments need to have originally been cut with the same restriction enzyme. This means that the sticky ends are complementary allowing the bases to pair up and form hydrogen bonds. DNA ligase then seals the sugar-phosphate backbone.

 

 

  • state other vectors into which fragments on DNA may be incorporated

Vectors carry the desired gene to the recipient cell. The most common vectors are bacterial plasmids sealed using DNA ligase. Others include virus genomes and yeast cell chromosomes. Vectors often have to contain regulatory sequences of DNA to ensure that the inserted gene is transcribed in the host cell.

  • explain how plasmids may be taken up by bacterial cells in order to produce a transgenic microorganism that can express a desired gene product

Plasmid – a small circular piece of DNA. Plasmids are found in many types of bacteria and are separate from the main bacterial chromosome. Recombinant plasmids form from the joining of a plasmid and the desired gene using restriction enzymes and DNA ligase. However, it is important to remember that many cut plasmids will, in the presence of ligase enzymes, simply reseal to reform the original plasmid.

Large quantities of the plasmid are mixed with bacterial cells, some of which will take up the recombinant plasmid. The addition of calcium salts and ‘heat shock’ (temperature is lowered to around freezing, then quickly raised to 40oC) increases the rate at which plasmids are taken up by bacterial cells. Even so, the process is very inefficient – less than a quarter of 1% of bacterial cells take up a plasmid.

Transformed bacteria – bacterial cells that take up the plasmid.

Transgenic organism – an organism that contains DNA that has been added to its cells as a result from genetic engineering.

Conjugation:

Conjugation is the process in bacteria where genetic material is exchanged. In this process, copies of plasmid DNA are passed between bacteria, sometimes even of different species.

  1. A conjugation tube forms between a donor and a recipient. An enzyme makes a nick in the plasmid.
  2. Plasmid DNA replication The free DNA strands starts moving through the tube.
  3. In the recipient cell, replication starts on the transferred DNA.
  4. The cells move apart and the plasmid in each forms a circle.

Evidence for Conjugation:

  • R-strain of Pneumococcus = mouse lives.
  • S-strain of Pneumococcus = mouse dies.
  • It was found that only mice infected with the S-strain were killed by a protein that was toxic – S-strain must have the instructions to make the protein but the R-strain does not.
  • Heat-treated S-strain of Pneumococcus = mouse livesno protein synthesis.
  • R-strain and heat-treated S-strain of pneumococcus = mouse dies.
  • The R-strain was capable of taking up DNA from their surroundings (DNA from S-strain), so synthesis of the toxic protein occurred and killed the mouse.
  • describe the advantages to microorganisms of the capacity to take up plasmid DNA from the environment

The advantage to the bacteria of conjugation is that it may contribute to genetic variation. Bacteria can gain useful characteristics, so they’re more likely to have an advantage over other microorganisms, which increases their chance of survival. Plasmids may contain:

  • Genes that code for resistance to antibiotics, e.g. genes for enzymes that break down antibiotics.
  • Genes that help microorganisms invade hosts, e.g. genes for enzymes that break down host tissues.
  • Genes that mean microorganisms can use different nutrients, e.g. genes for enzymes that break down sugars not normally used.
  • outline how genetic markers in plasmids can be used to identify the bacteria that have taken up a recombinant plasmid

  1. Plasmids are carry ampicillin and tetracycline resistant genes are chosen as they are resistant to the antibiotics ampicillin and tetracycline. The resistance genes are known as genetic markers.
  2. The plasmids are cut by a restriction enzyme that has its target site in the middle of the tetracycline resistance gene. The gene for tetracycline resistance is broken up and does not work, however, the gene for ampicillin resistance still works.
  3. Replica Plating:
  • The plasmids are mixed with bacteria, some of which will take up the plasmids. The bacteria are grown on standard nutrient agar, so all bacterial cells grow to form colonies.
  • Some cells from the colonies are transferred onto agar that has been made with ampicillin – only those that have taken up a plasmid will grow.
  • Some cells from the colonies are transferred onto agar that has been made with tetracycline – only those that have taken up a plasmid that does not have the insulin gene will grow.
  1. By keeping a track of which colonies are which, we know that any bacteria that grow on the ampicillin agar, but not on the tetracycline agar, must have taken up the plasmid with the insulin These bacteria can then be grown on a large scale to harvest insulin.
  • outline the process involved in the genetic engineering of bacteria to produce human insulin

People who cannot produce the hormone insulin suffer from type I diabetes mellitus. Until the early 1980s, insulin was extracted from the pancreatic tissues of slaughtered pigs, which is not identical to human insulin, is less effective and very expensive to produce, since only a very small amount of insulin is present in pancreatic tissue.

  1. mRNA is extracted from the β-cells of the pancreas.
  2. Reverse transcriptase is used to synthesise a complementary DNA strand.
  3. DNA polymerase and DNA nucleotides produce a copy of the original gene (cDNA gene) in a PCR machine.
  4. Plasmid is extracted from coli and cut open with restriction enzymes at the restriction site.
  5. The plasmid is mixed with the cDNA genes and some plasmids take up the gene. DNA ligase then seals up the plasmids creating a recombinant plasmid.
  6. The plasmids are mixed with bacteria, some of which take up the recombinant plasmids.
  7. The bacteria are grown on agar plates, where each bacterial cell grows to produce a colony.
  • outline the process involved in the genetic engineering of ‘Golden RiceTM

Golden RiceTM is a type of genetically engineered rice produced to reduce vitamin A deficiency. Vitamin A (retinol) in the diet only comes from animal sources. In vegetarians and those without access to meat, vitamin A is derived from the intake of beta-carotene (precursor), which is converted to active vitamin A in the gut.

Rice plants (Oryza sativa) contain the gene that code for the production of beta-carotene. Unfortunately, in the plant of the plant that is eaten – the endosperm (grain) – the genes for beta-carotene production are switched off. It was found that insertion of two genes into the rice genome was needed in order for the metabolic pathway to create beta-carotene to be activated in the endosperm cells.

  1. The genes that give Golden RiceTM its ability to make beta-carotene in the endosperm are obtained from daffodil plants (Phytoene synthetase) and from the soil bacterium Erwinia uredovora (Crt 1 enzyme) using restriction enzymes.
  2. A plasmid is removed from the Agrobacterium tumefaciens bacterium and cut open with the same restriction enzymes. The genes that code for the enzymes Phytoene synthetase and Crt 1 enzyme are inserted into the plasmid using ligase enzymes.
  3. The recombinant plasmid is put back into the bacterium. Rice plant cells are incubated with the transformed tumefaciens bacteria, which infect the rice plant cells.
  4. tumefaciens bacteria inserts the genes into the plant cells’ DNA, creating transformed rice plant cells.

  • outline how animals can be genetically engineered for xenotransplantation

Xenotransplantation – transplantation of cell tissues or organs between animals of different species.

Allotransplantation – transplantation of cells tissue or organs between animals of the same species.

Engineered Pigs as Organ Donors:

α-1,3-transferase is the enzyme a key trigger in transplant rejection in humans. In 2003, it was reported that pigs engineered to lack the enzyme α-1,3-transferase had been successfully developed. In 2006, scientists reported that engineering of the human nucleotidase enzyme (E5’N) into pig cells in culture reduced the active of a number of immune cell activities involved in xenotransplant rejection. These developments have encouraged xenotransplantation between pigs and humans.

  • explain the term gene therapy

Gene Therapy – adding new alleles to the DNA of cells to treat genetic disorders – we are only able to treat recessive disorders.

In simple terms, if the working copy of a gene is placed into cells that contain only the dysfunctional copies of that gene, then transcription of the added working copy will mean that the individual may no longer have the symptoms associated with the genetic disorder.

  • explain the difference between somatic cell gene therapy and germ line cell gene therapy

Somatic Cell Gene Therapy:

This method uses fully differentiated cells (adult, fully-grown, developed cells found in the body) with specific genes switched on or off to suit their requirements.

  • Augmentation (adding genes) – applies to conditions that are caused by inheritance of faulty alleles and leads to the loss of a functional gene product. Engineering a functional copy of the gene into relevant specialised cells means that the polypeptide is synthesised and the cells can be function normally. However, this can only happen with recessive diseases.
  • Killing Specific Cells – e.g. cancers, genetic techniques can be used to make cancerous cells express genes to produce proteins (such as cell surface antigens) that make the cells vulnerable to attack by the immune system could lead to targeted cancer treatments.

Germline Cell Gene Therapy:

This method uses undifferentiated, totipotent cells (zygote, early embryonic cells, sperm, egg cells). Cells of an early embryo are stem cells – it can divide and specialise to become any cell type within the body. Engineering a gene into these stem cells or sperm, eggs or zygotes means that as the organism grows every cell contains a copy of the engineered gene. This gene can then function within any cell where that gene is required. Although wildly employed in experimental animals, germline gene therapy in humans is illegal and ethically unacceptable.

  • discuss the ethical concerns raised by the genetic manipulation of animals (including humans), plants and microorganisms

 

 

 

 

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Cloning in Plants and Animals

Cloning in Plants and Animals

  • outline the differences between reproductive and non-reproductive cloning

Clones – genes, cells or whole organisms that carry identical genetic material because they are derived from the same original DNA.

Reproductive cloning generates genetically identical organisms.

Non-reproductive cloning generates cells, tissues and organs – can replace those damaged by diseases or accidents.

The advantages of using cloned cells include:

  • Cells won’t be rejected as they’re genetically identical to an individual’s own cells.
  • Prevent waiting for donor organs to become available for transplant.
  • Cloned cells can be used to generate any cell type because they are totipotent. Damage caused by some diseases and accidents cannot currently be repaired by transplantation or other treatments.
  • Using cloned cells is less likely to be dangerous than a major operation such as a heart transplant.

There are many possibilities for non-reproductive cloning, including:

  • The regeneration of heart muscle cells following a heart attack.
  • The repair of the nervous tissue destroyed by diseases such as multiple sclerosis.
  • Repairing the spinal cord of those paralysed by an accident that results in a broken back or neck.

These techniques are often referred to as therapeutic cloning. However, there are some ethical issues concerning whether cloning should be used in humans. There are ethical objections to the use of human embryonic material and some scientific concerns about a lack of understanding of how cloned cells will behave over time.

  • describe the production of natural clones and in plants using the example of vegetative propagation in elm trees

Natural Vegetative Propagation:

Vegetative propagation is form of asexual reproduction of a plant. Only one plant is involved and the offspring is the result of one parent. The new plant is genetically identical to the parent.

  1. Runners – stems that grow horizontally above the ground. They have nodes where buds are formed, which grow into a new plant, e.g. strawberries and spider plant.
  2. Tubers – new plants will grow out of swollen modified roots called tubers. Buds develop at the base of the stem and then grow into new plants, e.g. potato and daliahs.
  3. Bulbs – a bulb contains an underground stem, with leaves containing stored food At the centre of the bulb is an apical bud, which produces leaves and flowers. Also attached are lateral buds, which produces new shoots, e.g. daffodils.
  4. Basal sprouts (root suckers) – the suckers grow from meristem tissue in the trunk close to the ground, where least damage is likely to have occurred, e.g. elm trees and mint. Root suckers help the elm spread, because they can grow all around the original trunk. When the trunk dies, the suckers grow into a circle of new elms called a clonal patch. This, in turn, puts out new suckers so that the patch keeps expanding as far as resources permit.

  • describe the production of artificial clones of plants from tissue culture

Artificial Vegetative Propagation:

  • Taking Cuttings – e.g. geraniums, a section of the stem is cut between leaf joints (nodes). The cut end of the stem is then often treated with plant hormones to encourage root growth, and planted. The cutting forms a new plant, which is a clone of the original parent plant.
  • Grafting – e.g. fruit tree or rosebush, a rootstock is cut to match the wedge-shaped stem to be grafted. The vascular tissue is lined up then binding is wrapped around the graft area to hold it in place until growth supports the grafted section. The graft grows and is genetically identical to the parent plant, but the rootstock is genetically different.
  • Using Tissue Culture – used in order to generate huge numbers of genetically identical plants successfully from a very small amount of plant material. The most common method used in the large-scale cloning of plants is micropropagation, e.g. orchids.
  1. A small piece of tissue is taken from the plant to be cloned, usually from the shoot tip (meristem) – explant.

  2. The explant is placed on a nutrient growth medium.
  3. Cells in the tissue divide. They do not differentiate, but form a mass of undifferentiated cellscallus.
  4. After a few weeks, single callus cells can be removed from the mass and placed on a growing medium containing plant hormones that encourage shoot growth.
  5. After a few weeks, the growing shoots are transferred onto a different growing medium containing different hormone concentrations that encourage root growth.
  6. The growing plants are then transferred to a greenhouse to be acclimatised and grown further before they are planted outside.

  • describe how artificial clones of animals can be produced

Totipotent – stem cells capable of differentiating into any type of adult cell found in the organism.

In animals, only embryonic cells are naturally capable of going through the stages of development in order to generate a new individual. These cells are totipotent stem cells and they are capable of differentiating into any type of adult cell found in the organism. There are two methods of artificially cloning animals:

Method 1: Splitting Embryos

Cells from a developing embryo can be separated out, with each one then going on to produce a separate, genetically identical organism.

  1. Collect eggs from a high-value female (e.g. high milk yield in cows) and collect sperm from a high-value male.
  2. In vitro fertilisation occurs between the eggs and the sperm.
  3. Grow the in vitro to a 16-cell embryo.
  4. Split the embryo into several separate segments and implant into surrogate mothers.
  5. Each calf produced is a clone.

Method 2: Nuclear Transfer

A differentiated cell from an adult can be taken, and its nucleus placed in an egg cell which has had its own nucleus removed (enucleated cell). The egg then goes through the stages of development using genetic information from the inserted nucleus. The first animal cloned by this method was Dolly the sheep in 1996, which was successful after 277 attempts.

  1. Remove mammary cells from Finn Dorset and place in culture. Remove an ovum (egg) from Scottish Blackface and remove the nucleus to produce an enucleate ovum.
  2. Electro-fuse the mammary cell and enucleate ovum together to create a reconstructed cell with Scottish Blackface cytoplasm and Finn Dorset nucleus.
  3. ‘Culture’ in tied oviduct in sheep.
  4. Recover the early embryo and implant the embryo in surrogate mother ewe’s uterus.
  5. ‘Dolly’, a Finn Dorset Ewe is born.

 

 

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