enzymes (chap 4) -olevel pure bio

what are enzymes

• proteins that function as biological catalysts

• speed up the rate of chemical reactions by lowering the activation energy needed to start a reaction

• remain chemically unchanged at the end of a reaction

what is a catalyst

a substance that can speed up a chemical reaction without itself being changed at the end of the reaction

what are the characteristics of enzymes

1. enzymes speed up chemical reactions -it lowers the activation energy needed to start a reaction

2. enzymes are specific in nature - only substrates with a shape complementary to the active site of the enzyme can bind with the enzyme and cause a chemical reaction

3. enzymes are only required in minute quantities and remain chemically unchanged after a reaction - enzymes can be used over and over again so only a small amount of an enzyme can catalyse the reaction for a large amount of substrate

4. enzymes are affected by temperature

5. enzymes are affected by pH - they are denatured by pH that is too far from the optimum pH

pls explain this temperature graph and label each part yk

1. enzyme is less active at lower temperatures as kinetic energy of molecules is low, so enzymes and substrates move more slowly and the rate of substrate colliding with enzyme is low.

2. as the temperature increases, kinetic energy increases and there’s a higher chance of substrate colliding into enzyme molecules, so rate is increased

3. this is the optimum temperature where the enzyme is most active

4. increasing temperature above the optimum causes the active site of the enzyme to denature and lose its shape and hence its shape is no longer complementary to the shape of substrate molecules

5. all enzymes are denatured and enzyme substrate reactions can no longer occur

explain the lock and key hypothesis

• the enzyme is the lock and the substrate is the key

• the shape of the enzyme active site is complementary to the substrate

• when a substrate is bonded to the active site of an enzyme, an enzyme-substrate complex is formed

• chemical reactions take place at the active site to convert the substrate into the product

• the product separates from the enzyme

• the enzyme remains unchanged and is free to combine with ore substrate molecules.