Enzymes

Question 1

Enzymes

Answer 1

• biological catalysts
• globular proteins
• allow faster rates of reaction without need for harsh conditions
• tertiary structure of active site is complimentary to shape of substrate
• specific to their substrates
• reduces Ea needed by creating new pathway
• Vmax = maximum rate of reaction

Question 2

Key Enzymes

Answer 2

CATALASE (intracellular)
- binds to hydrogen peroxide (toxic)
- ^ speeds up H₂O₂ decomposition to produce H₂O + O

AMYLASE (extracellular)
- produced in salivary glands & pancreas
- released in small intestine
- catalyses reaction of starch to maltose

TRYPSIN (extracellular)
- produced in pancreas
- catalyses reaction of proteins to peptides

Question 3

Induced Fit Model

Answer 3

1. tertiary s. of enzyme adjusts as substrate approaches
2. R-groups in active site interact w/ substrate to form ‘temporary bonds’
3. active site moulds itself around substrate as bonds form

Question 4

Induced Fit Model 2

Answer 4

• non-substrates cannot form correct bonds w/ amino acids
• ^ tertiary structure of enzyme doesn’t change
• ‘Lock & Key’ model is a limited explanation for enzyme process
• ^ states active site is ‘fixed’ in shape

Question 5

Concentration

Question 6

pH

Question 7

Inhibition

Answer 7

• prevent enzymes from carrying out normal functions
• slows down rate of reaction
• irreversible inhibitors are usually toxic e.g. insecticides

COMPETITIVE (e.g. statins)
- molecule w/ similar shape to substrate binds to active site
- substrate & inhibitor compete in solution to bind
- ^ reduces number of enzyme-substrate complexes forming
- effects of inhibitor are reversible

NON-COMPETITIVE
- inhibitor binds to the ‘allosteric site’
- ^ causes tertiary s. of enzyme to change; active site changes shape
- active site is no longer complementary to substrate

Question 8

End-product Inhibition

Answer 8

• product acts as the inhibitor to enzyme that produces it
• aka ^ ‘negative feedback control mechanism’
• ATP regulates it’s own production
• ^ it binds to the allosteric site of PFK (enzyme for initial breakdown of glucose)
• ^ this prevents addition of the 2nd phosphate group to glucose

Question 9

Co-factors, Co-enzymes & Prosthetic groups

Answer 9

• ‘co-enzyme’ = an organic co-factor
• co-factors are obtained through diet as minerals e.g. iron, calcium & zinc ions
• ^ some are loosely/temporarily bound to enzyme protein
• amylase contains a chloride ion essential for formation of active site
• co-enzymes derive from vitamins e.g. vitamin B5 in the synthesis of ‘co-enzyme A’
• prosthetic groups are co-factors
• ^ they’re tightly bound & form a permanent feature of the protein

Question 10

Precursor Activation

Answer 10

• enzymes produced in an inactive form
• due to possible cell damage, control of enzyme action OR for enzymes needed in specific conditions
• precursor enzymes need a change in their tertiary s. to be activated
• ^ this happens by adding a co-factor
• ‘apoenzyme’ = p. enzyme before co-factor is added
• ‘holoenzyme’ = p. enzyme after co-factor is added
• ‘proenzyme’ = an enzymes activated due to a change in condition of solution e.g. temperature