ENZYMES

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Substrate: the reactant that an enzyme acts on

when it catalyzes a chemical reaction

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Controlling Enzyme Activity

Competitive Inhibition• A substrate mimic (molecule that has the same

configuration as the substrate) can enter into ACTIVE SITE and block enzyme action.

• Some antibiotics are competitive inhibitors– E.g.; HIV (protease inhibitors)

– Penecillin (inhibits a bacteria transpepsidase: cell wall is not built properly)

• When bind permanently: poisons or toxins• When bind temporarily: can be “disloged” by

increasing concentration of substrate

Allosteric Inhibition (Non-competitive inhibition)

• A substance binds to the enzyme at some other site (NOT the active site). This causes the enzyme to change shape and the active site is not available.

• When the substance falls off the enzyme, the enzyme returns to its normal shape and become available again

a) Substrate and enzyme

b) Competitive Inhibitor

c) Non competitive inhibitor

ENZYME DENATURATION

• Temperature and pH are important environmental factors for enzyme activity.

• If temperature is too low or too high, this will change the ability of the enzyme to bind to the substrate.

• High temperatures cause the bonds holding the enzyme to break…this changes the shape of the protein and its active site. This may be temporary or permanent depending on how many and what kinds of bonds are disrupted.

                                                                 

• When temperatures are too low, the enzyme is not denatured but the slower kinetic energy of the molecules means that less collisions will occur between the enzyme and its substrate.

• Techniques of deep-freezing are commonly used to preserve food for extensive periods. The very low temperature not only prevents the growth and multiplication of micro-organisms, but also inactivates their digestive enzymes and the natural enzymes present in the food itself,thus making it impossible for them to decompose the food.

• pH can affect enzymes by disrupting the ionic and hydrogen bonds that hold the enzymes shape.

• The optimum pH is NOT the same for all enzymes