(3.1.4.2) many proteins are enzymes

Question 1

what are enzymes?

Answer 1

tertiary structured proteins that increase the rate of reaction (by lowering the activation energy) without getting used up themselves.

Question 2

how do enzymes lower the activation energy?

Answer 2

• by bending the bonds in the substrate, putting strain on the bonds to make them more likely to break
• bringing two molecules close together, overcoming the natural repulsion, making a bond between the two more likely

Question 3

explain how the active site of an enzyme causes a high rate of reaction

Answer 3

1. active site is complementary to substrate and binds to it, forming a enzyme-substrate complex
2. induced fit causes a slight change to the active site’s shape
3. e.s.c causes bonds to bend, causing them to break more readily, leading to reaction

Question 4

what are five factors affecting enzyme-controlled reactions?

Answer 4

• temperature
• pH
• enzyme concentration
• substrate concentration
• inhibitors

Question 5

explain why there is a increased rate of reaction with an increased temperature

Answer 5

1. particles have more kinetic energy therefore they move more
2. so there are more collisions between substrates and active sites
3. so more ES complexes form

Question 6

explain the effect of changes in pH on the rate of enzyme-controlled reactions

Answer 6

1. ionic bonds holding tertiary structure break
2. active site distorts and substrate no longer binds to active site
3. charges on amino acids in active site affected
4. fewer ES complexes form

Question 7

explain how enzyme can denature

Answer 7

1. heat above the optimum breaks hydrogen bonds, causing the tertiary structure to unfold
2. so the active site changes shape 4. substrate can no longer bind to the active site, as it’s no longer complementary
3. so fewer ES complexes form

Question 8

explain how enzyme concentration effects the rate of enzyme-controlled reactions

Answer 8

• at low concentrations, rate of reaction increases due to more enzyme-substrate complexes being formed
• at high concentrations, rate of reaction plateaus due to there being more enzymes than substrates; substrate concentration becoming the limiting factor

Question 9

explain how substrate concentration effects the rate of enzyme-controlled reactions

Answer 9

• at low concentrations, rate of reaction increases due to more enzyme-substrate complexes being formed
• at high concentrations, rate of reaction plateaus due to there being more substrates than enzymes; enzyme concentration becoming the limiting factor

Question 10

explain how a competitive inhibitor effects the rate of reaction

Answer 10

they have a similar shape to the substrate, meaning they can bind to the active site, blocking the substrate from binding.

this reduces the formation of enzyme-substrate complexes which reduces the rate of reaction.

Question 11

explain how a non-competitive inhibitor effects the rate of reaction

Answer 11

they bind to the allosteric site of the enzyme, causing a change in the shape of the active site, making it no longer complementary to the substrate.

this reduces the formation of enzyme-substrate complexes which reduces the rate of reaction.