1.5 Enzymes

Question 1

name three properties of enzymes

Answer 1

biological catalysts
specific shape
lower activation energy
proteins with a tertiary/globular structure

Question 2

describe an anabolic reaction

Answer 2

catalysed by anabolic enzymes
involves making bonds
includes building up larger molecules
e.g. protein synthes

Question 3

describe a catabolic reaction

Answer 3

catalysed by catabolic enzymes
involves breaking bonds
produces smaller molecules
e.g. digestion

Question 4

describe the lock + key hypothesis of enzyme action

Answer 4

1. the enzyme’s active site and the substrate have complementary shapes
2. the substrate binds onto the active site of the enzyme
3. an enzyme-substrate complex forms
4. the enzyme reduces the activation energy required to break bonds in the substrate
5. products move away from the active site + enzyme is reusable

Question 5

described the induced fit theory of enzyme action

Answer 5

• suggests that enzymes induce their active site to have a complementary shape with the substrate
• when products are formed, the enzyme returns to its original shape

Question 6

factors affecting enzyme action

Answer 6

enzyme concentration
substrate concentration
temperature
pH 
co-factors
inhibitors

Question 7

describe how a competitive inhibitor works

Answer 7

• the substrate and competitive inhibitor have a similar shape
• competitive inhibitor fits into the active site, blocking the substrate
• rate of reaction is reduced
• reversible

Question 8

describe how a non-competitive inhibitor works

Answer 8

non-competitive inhibitors bind somewhere other than the active site

• causes a permanent change to the shape of the active site
• irreversible

Question 9

describe the effect of temperature on enzymes

Answer 9

1. as the temperature increases, kinetic energy of the molecules increases
   this means the enzyme and substrate are more likely to collide and form enzyme-substrate complexes so rate of reaction INCREASES
2. after the optimum temp is reached, kinetic energy causes intramolecular vibration that breaks bonds within the enzyme so the active site changes
   this means enzyme-substrate complexes cannot form
   rate of reaction DECREASES

Question 10

describe the effect of pH on enzymes

Answer 10

in highly acidic or alkaline environments, H+ or OH- ions interact with amino acids in the enzyme, breaking bonds and altering the shape of the active site, causing the enzyme to denature