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Cell Structure #2

Microscopes

Light microscope – Light microscopes shine light through a specimen and then uses focused lenses to magnify it.

Laser scanning microscope – These use laser light to scan an object, point by point, before using the information to assemble an image on the computer. They create very high definition, high contrast images and have depth selectivity (they can focus on structures at different depths in the specimen). They are used for biological research and in the medical progression e.g. to use on a patient with a fungal corneal infection as the fungal filaments within the cornea will be visible on the microscope image. It helps give faster diagnosis so the treatment is given earlier and is therefore more effective.

  1. Nerve Cell

  1. Lung tissue

  1. Plant vascular bundle

  1. E.Coli bacteria

  2. Mitochondria

Magnification

The magnification is how many times bigger an image is compared to the original specimen. Microscopes produce linear magnification. (it’s width and length are magnified by the same amount)

Magnification = Size of Image/Size of Object

Size of Object = Size of image/Magnification

Size of image = Size of Object x Magnification

 

Resolution

Resolution is the microscopes ability to show fine detail and produce clear, sharp images.

An eyepiece graticule is an eye piece that fits on a microscope with a ruler etched into it. The ruler has 100 divisions which are measured in Eye Piece Units or EPU’s. To calibrate the eyepiece graticule a graticule slide is placed under the light microscope with another ruler displaying either 1cm or 1mm in 100 divisions. Using the graticule slide, we can calibrate the lens to work out how long each division on the eyepiece would be after the image is magnified. The image of the ruler is then superimposed over your slide sample so that you can use the scale you have worked out with the graticule slide to measure samples and specimens.

Stage graticules are available in two types

  • (book) 1mm long graticule with 100 divisions. 1mm = 1000μm so each division = 10µm
  • (class) 1cm long graticule with 100 divisions. 1cm = 10000µm so each division = 100µm

 

 

Eukaryotic Cells

  • Robert Hooke 1665 discovered cells
  • Cilia/flagellum – long whip like tail made of microtubules
  • Cell membrane – encloses the cell contents, selective permeability, flexible
  • Cytoplasm – water and nutrients, contains the cytoskeleton and centrosomes which assemble microtubules
  • Endoplasmic reticulum – phospholipid bilayer: Rough – ribosomes and create protein: Smooth – enzymes create lipids cell detox and stores ions such as sodium ions
  • Ribosomes assemble amino acids into poly peptides
  • Nucleus – nucleoplasm inside, stores the cell’s DNA, chromatic holds the DNA, Cell division means the chromatin makes chromosomes Nucleolus makes rRNA combines with proteins which makes ribosomes
  • Golgi apparatus – processes and packaging and sends them out, contains Golgi bodies – these are the Golgi apparatus layers, proteins cut up into smaller hormones and combine proteins with carbs to make various molecules e.g. mucus
  • Lysosomes – cell digestion, enzyme sacks, cell waste >> simple compounds used for building materials
  • Vesicles – phospholipid bilayer, responsible for transporting substances around the body
  • Mitochondria – respiration – makes energy adenosine tri-phosphate, muscle cells need more energy so have more mitochondria, they used to exist as prokaryotes and contain a small amount of DNA

Eukaryotic Animal Cell

Mitochondrion

Mitochondria are double membrane structures enclosing a semi-fluid matrix, in which aerobic respiration (ATP synthesis) occurs, producing the energy the cell needs to move, contract, divide, and produce secretory products. The outer membrane of a mitochondrion is smooth, whereas the inner membrane forms cristae (folds) and is very convoluted. On the cristae, simple sugars such as glucose are combined with oxygen to produce ATP. Both the cristae and the semi-fluid matrix contain the enzymes that allow for aerobic respiration.

Vesicle – Lysosome

Lysosomes assist in intracellular digestion as they contain hydrolytic enzymes that break down bacteria. In a white blood cell, lysosomes are released into the vacuole to kill and digest the bacteria the cell has engulfed. Having to many lysosomes in the cytoplasm can cause necrosis.

Plasma Membrane/Cell Surface Membrane

The plasma membrane is a bilayer of phospholipid molecules with hydrophilic heads and hydrophobic tails, there are protein channels set into the barrier to transport substances into the cell. It’s function is to be a partially permeable membrane that provides protection and physical allows the import and export of chemicals and substances to and from the cell.

Golgi Apparatus

The Golgi apparatus is membrane-bound structure composed of a single membrane that binds a stack of large vesicles in a network, where they can modify and package proteins for transport. The stack of large vesicles

is surrounded by many smaller vesicles that contain the packaged protein macromolecules. The enzymatic/hormonal contents of lysosomes, peroxisomes and secretory vesicles are also packaged in vesicles at the periphery of this organelle. The vesicles can become detached from the Golgi which allows chemicals to be kept isolated from each other in the cytoplasm. These detached vesicles allow for secretion by merging with the plasma membrane of the cells surface.

Peroxisome

These are membrane bound packets of oxidative enzymes responsible for turning hydrogen peroxide into harmless water and oxygen.

Cytoplasm/Cytosol

The cytoplasm is the semi-liquid medium that the animal cell’s organelles are suspended in. It makes up the main body of the cell, contains many dissolved ions and is the site of most chemical reactions within the cell.

Cytoskeleton

The cytoskeleton is composed of microfilaments, microtubules and intermediate filaments and functions for both movement and support in the cell.

Smooth Endoplasmic Reticulum (SER)

The smooth endoplasmic reticulum is a continuation of the outer nuclear membrane. It assists the synthesis and transport of lipids. Unlike the rough endoplasmic reticulum, the smooth ER doesn’t have ribosomes.

Nuclear Pore

Nuclear pores are protein lined channels that regulate the transport of chemicals and substances to and from the nucleus. mRNA moves in and out of these entrances.

Centrioles/Microtubules

Centrioles are the two short cylinders which contain a ring of nine groups of fused microtubules, with three in each group. These migrate to the opposite poles to aid cell division when the spindle begins to develop. Microtubules and centrioles are part of the cytoskeleton.

Secretory Vesicles

Hormones and neurotransmitters and other cell secretions are packaged in the secretory vesicles at the Golgi apparatus. The vesicles are then transported to the cell membrane where they can release the cell secretions outside the cell.

Nucleolus

The nucleolus is where RNA and ribosomes are made within the nucleus. It is made of proteins and unlike many of the cell organelles in an animal cell, is not a membrane bound structure

Vacuole

Vacuoles are membrane bound sacks that aid in intracellular digestion, storing nutrients and waste products and increasing the size of the cell during growth. In animal cells, vacuoles are generally small, unlike in plant cells where they are generally larger.

Rough Endoplasmic Reticulum (RER)

A folded membrane structure and a continuation of the outer nuclear membrane, the rough endoplasmic reticulum is very similar to the smooth. However the RER has ribosomes which synthesize proteins, before they are collected in the RER for transport around the cell.

 

Centrosome/Microtubule Organizing Centre (MTOC)

A centrosome/microtubule organizing centre (MTOC) is the area of the cell that produces microtubules. A complete animal cell centrosome is a pair of centrioles held perpendicular to each other. At cell division, the centrioles replicate and the centrosome divides, resulting in two centrosomes with a pair of centrioles each. They migrate to the cells poles and there microtubules grow into a spindle, responsible for separating replicated chromosomes into the two daughter cells the original animal cell will divide into.

Ribosomes

Ribosomes are the site of protein synthesis. The protein chains are lengthened by transfer RNA adding individual amino acids to the messenger RNA strand that the nucleus has sent to the ribosomes. Ribosomes are structured in two parts, a large subunit and a small subunit. They are full of RNA.

 

Cell Wall

In plants this is made of cellulose and is strong to prevent cells from bursting when turgid. They provide support, maintain the cells shape and allow solutions to pass through. Fungi have cell walls of chitin and not cellulose.

Prokaryotic Cells

Prokaryotic cells are much smaller than eukaryotic and do not contain some of the organelles present in eukaryotes. They do not have centrioles or a nucleus and so divide by binary fission. They also do not have membrane bound organelles (e.g. ER and Golgi). Around their edge they sometimes have a waxy capsule and a cell wall made of peptidoglycan as well as pili and flagella. Instead of a nucleus the cell stores its genetic material in the plasmid and a nucleoid. Its ribosomes are smaller and it contains starch granules as well.