1.5Enzymes

Question 1

describe the structure of an enzyme

Answer 1

Globular proteins

Specific tertiary structure determines shape of active site, complementary to specific substrate

Question 2

Explain the function of enzymes

Answer 2

biological catalysts for intra and extracellular reactions.

formation of enzyme-substrate (ES) comlexes lowers activation energy of metabolic reactions

Question 3

Explain the induced fit model of enzyme action

Answer 3

Shape of active site is not directly complementary to substrate and is flexible.
confornmation change enables ES complexes to form.

this puts strain on substrate bonds, lowering activation energy.

Question 4

Name 5 factors that affect the rate of enzyme-controlled reactions

Answer 4

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

Question 5

how does substrate concentration affect rate of reactions?

Answer 5

Given that enzyme concentration is fixed, rate increases proportionally to substrate concentration

rate levels off when maximum number of ES complexes form at any given time.

Question 6

How does enzyme concentration affect rate of reaction?

Answer 6

Given that substrate is excess, rate increases proportionally to enzyme concentration

Rate levels off when maximum number of ES complexes form at any given time.

Question 7

How does pH affect rate of reaction?

Answer 7

Enzymes have a narrow optimum pH range.

Outside range, H+/OH- ions interact with H-bonds and ionic bonds in 3 degrees structure = denaturation

H+ can bond with R groups of amino acids in the protein (enzymes)
this includes amino acids within the active site
which form temporary bonds to the substrate

this can prevent these R groups from bonding with the substrate
- which reduces how effective the substrate binds to the the active site
- reducing rate of reaction

Question 8

How do competitive inhibitors work?

Answer 8

Bind to active site since they have similar shape to substrate. Temporarily prevent ES complexes from forming until released.
increasing substrate concentration decrease their effect

Question 9

how do non-competitive inhibitors work?

Answer 9

Bind at allosteric binding site

trigger conformational change of active site

increasing substrate concentration has no impact on their effect.

Question 10

what is end-product inhibition

Answer 10

one of the products of a reaction acts as a competitive or non-competitive inhibitor for an enzyme involved in the pathaway. prevents further formation of products.

Question 11

outline how to calculate initial rate from a graph.

Answer 11

calculate gradient of tangent at t=0

Question 12

why is it advantageous to calculate initial rate

Answer 12

represents maximum rate of reaction before concentration of reactants decreases and end-product inhibition.