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Enzymes

2.1.3 Enzymes

(a) state that enzymes are globular proteins, with a specific tertiary structure, which catalyse metabolic reactions in living organisms

All enzymes are globular proteins with a specific tertiary structure, which catalyse metabolic reactions in all living organisms. This means that they speed up chemical reactions, but are not ‘used-up’ as part of the reaction.

Enzymes are relatively large molecules, consisting of hundreds of amino acids which are responsible for maintaining the specific tertiary structure of the enzyme. Each enzyme has a specific active site shape, maintained by the specific overall tertiary structure. Therefore the tertiary structure must not be changed.

(b) state that enzyme action may be intracellular or extracellular

Extracellular enzyme action occurs outside the cell, which produces the protein. For example, some enzymes in digestive systems are extracellular as they are released from the cells that make them, onto food within the digestive system spaces.

Intracellular enzyme action occurs inside the cell, which produces the enzyme. For example, some enzymes in digestive systems are found in the cytoplasm of cells or attached to cell membranes and the reaction takes place inside the cell.

 

(c) describe, with the aid of diagrams, the mechanism of action of enzyme molecules, with reference to specificity, active site, lock and key hypothesis, induced-fit hypothesis, enzyme-substrate complex, enzyme-product complex and lowering of activation energy.

 

The activation energy is the minimum level of energy required to enable a reaction to take place. Enzymes work by lowering the activation energy of reactions. This means reactions can proceed quickly at temperatures much lower than boiling point as less energy is required for the reaction.

 

(d) describe and explain the effects of pH, temperature, enzyme concentration and substrate concentration on enzyme activity

(e) describe how the effects of pH, temperature, enzyme concentration and substrate concentration on enzyme activity can be investigated experimentally

(f) explain the effects of competitive and non-competitive inhibitors on the rate of enzyme-controlled reactions, with reference to both reversible and non-reversible inhibitors

An enzyme inhibitor is any substance or molecule that slows down the rate of an enzyme-controlled reaction by affecting the enzyme molecule is some way.

Reversible inhibitors are inhibitors that bind to the active site for a short period and then leave. The removal of the inhibitor from the reacting mixture leaves the enzyme molecules unaffected.

 

Irreversible inhibitors are inhibitors that bind permanently to the enzyme molecule. Any enzyme molecules bound by inhibitor molecules are effectively denatured.

 

 

(g) explain the importance of cofactors and coenzymes in enzyme controlled reactions

A cofactor is any substance that must be present to ensure enzyme-controlled reactions can take place at the appropriate rate. Some cofactors are part of the enzymes (prosthetic groups); others affect the enzyme on a temporary basis (coenzymes and inorganic ion cofactors).

(h) state that metabolic poisons may be enzyme inhibitors, and describe the action of one named poison

(i) state that some medicinal drugs work by inhibiting the activity of enzymes