05) Enzymes

Question 1

1.1. Describe a catalyst

Answer 1

A substance that increases the rate of a chemical reaction and is not changed by the reaction

Question 2

1.2. Describe enzymes

Answer 2

Proteins that are involved in all metabolic reactions, where they function as biological catalysts

Question 3

1.3. Describe why enzymes are important in all living organisms

Answer 3

They maintain reaction speeds of all metabolic reactions (all the reactions that keep an organism alive) at a rate that can sustain life

For example, if we did not produce digestive enzymes, it would take around 2 - 3 weeks to digest one meal; with enzymes, it takes around 4 hours

Question 4

1.4/6. Describe and explain enzyme action

Answer 4

The shape of the active site of an enzyme is complementary to its substrate

1. Enzymes and substrates randomly move about in solution
2. When an enzyme and its complementary substrate randomly collide - with the substrate fitting into the active site of the enzyme - an enzyme-substrate complex forms, and the reaction occurs
3. A product (or products) forms from the substrate(s) which are then released from the active site. The enzyme is unchanged and will go on to catalyse further reactions.

Question 5

1.5/8. Investigate and describe the effect of changes in temperature on enzyme activity

Answer 5

Enzymes work fastest at their “optimum temperature” – 37⁰C in the human body. Heating beyond the optimum breaks the enzyme’s bonds and it will lose its shape - denaturation. Substrates don’t fit - the shape of their active site has been lost

Once enzymes are denatured they cannot regain their proper shape and activity will stop

Increasing the temperature from 0⁰C to the optimum increases the activity of enzymes as the more kinetic energy the molecules have the faster they move and the frequency of effective collisions with the substrate molecules increases, leading to a faster rate of reaction

Low temperatures do not denature enzymes, they just make them work more slowly

Question 6

1.7. Explain the specificity of enzymes

Answer 6

Enzymes are specific to one particular substrate(s) as the active site of the enzyme, where the substrate attaches, is a complementary shape to the substrate. The enzyme is a protein and has a specific 3-D shape. This is known as the lock and key hypothesis

When the substrate moves into the enzyme’s active site they become known as the enzyme-substrate complex. After the reaction has occurred, the products leave the enzyme’s active site as they no longer fit it and it is free to take up another substrate

Question 7

1.9. Explain the effect of changes in pH on
enzyme activity

Answer 7

The optimum pH for most enzymes is 7 but some produced in acidic conditions, like the stomach, have lower optimums (pH 2) and some produced in alkaline conditions, like the duodenum, have a higher optimum (pH 8 or 9)

If it’s too high or too low, the bonds holding the amino acid chain together to make up the protein can be destroyed, changing the shape of the active site so the substrate can no longer fit into it, reducing the rate of activity. Moving too far away from the optimum will denature the enzyme and activity will stop