Enzymes

Question 1

What type of protein are enzymes?

Answer 1

globular proteins?

Question 2

how do enzymes catalyse a reaction?

Answer 2

lower activation energy

Question 3

what is activation energy?

Answer 3

minimum amount of energy needed to start a reaction

Question 4

what is free energy?

Answer 4

energy of a system that is available to perform work

Question 5

list three conditions that must be satisfied for a reaction to take place

Answer 5

• molecules collide with sufficient energy
• products have less free energy than reactants
• activation energy

Question 6

what is the active site?

Answer 6

specific region where enzyme is functional and substrate binds

Question 7

why are enzymes highly specific?

Answer 7

due to tertiary structure

Question 8

name two types of reactions involving enzymes

Answer 8

• degradation - break down of food into nutrients

- synthesis - formation of products (condensation)

Question 9

what is the compound formed from an enzyme and substrate?

Answer 9

enzyme-substrate complex

Question 10

what are the two models of enzyme action?

Answer 10

• lock and key model

- induced fit model

Question 11

explain lock and key model

Answer 11

substrate is complementary to enzyme because it is specific

Question 12

explain induced fit model

Answer 12

substrate has similar shape but not exact shape needed so the enzyme moulds itself around the substrate and puts strain on particular bond/s in substrate which lowers activation energy

Question 13

why is induced fit model a better explanation?

Answer 13

explains how other molecules which bind to enzyme not on its active site affect the enzyme active site - enzyme structure is flexible whereas lock and key model suggests the structure is rigid

Question 14

how does increase in temperature affect enzyme action?

Answer 14

• increase in temp - lead to higher KE - more ES complex formed up to optimum
• after this high KE will break bonds in tertiary structure (hydrogen bonds/ ionic bonds/ disulphide bridges)
• shape of active site is altered so no ES complexes can be formed

Question 15

how does a cold temperature affect enzyme action?

Answer 15

enzymes have a lower KE therefore less collisions and less ES complex so less product formed - this means there is a lower rate of reaction

Question 16

how does change in pH affect enzyme action?

Answer 16

• disruption of attraction of hydrogen bonds alters the secondary protein structure
• also alters tertiary structure as ionic bonds also affected so active site changes

Question 17

how does enzyme concentration affect enzyme action ?

Answer 17

with an excess of substrate, as enzyme concentration increases, rate of reaction increases because more active sites to bind with substrates

Question 18

how does substrate concentration affect enzyme action?

Answer 18

as you increase substrate concentration, rate of reaction increases because more active sites are occupied
- after a while it has no effect because all active sites occupied

Question 19

what are cofactors?

Answer 19

substances that are present in a enzyme-catalysed reaction to ensure reaction occurs at appropriate rate
- bind temporarily to enzyme or substrate

Question 20

what are prosthetic groups?

Answer 20

cofactors which bind permanently to active site e.g. zinc ion for carbonic anhydrase

Question 21

what are coenzymes?

Answer 21

enzymes that bind temporarily to active site before or whilst substrate binds

• usually vitamins
• chemically changed by process

Question 22

what is competitive inhibition?

Answer 22

molecule similar shape to substrate so fits in active site

Question 23

when is inhibitors most successful?

Answer 23

at a low concentration of substrate because fewer substrate are converted

Question 24

how can competitive inhibition be reversed?

Answer 24

by adding more substrate

Question 25

what is non-competitive inhibition?

Answer 25

binds to another part of enzyme which disrupts tertiary structure (hydrogen bonds/ ionic bonds/ disulphide bridges) so alters active site

Question 26

how do non-competitive inhibitors affect rate of reaction at a low substrate concentration?

Answer 26

less substrate converted to product so lower rate of reaction

Question 27

what is end-product inhibition?

Answer 27

form of negative feedback where high concentration of end-product inhibits enzyme to prevent further production (e.g. insulin/glucose)