2.4 Enzymes (Spec)

Question 1

Extracellular enzyme

Answer 1

Synthesised in cell and secreted

Question 2

Intracellular enzyme

Answer 2

Synthesised in cell and retained

Question 3

Lock and key model

Answer 3

Enzyme and substrate are exactly complementary
Substrate approaches enzyme w/ complementary active site, binds -> enzyme-substrate complex
Substrates converted to products -> enzyme-product complex
Products released, active site unchanged, enzyme able to catalyse further reactions

Question 4

Induced-fit model

Answer 4

Substrate and enzyme are almost complementary
Substrate approaches enzyme w/ complementary/ almost complementary active site -> weak temporary bonds form
Temporary bonds -> Rapid, small changes in active site’s tertiary structure -> Active site exactly complementary
Strong bonds between enzyme and substrate -> enzyme-substrate complex
Strong bonds hold substrate(s) close together, less energy to orient reacting groups close to form bonds
Strong bonds place strain on substrate bonds, broken w/ less energy input, lowers activation energy
Substrate forms products -> enzyme-product complex
Products released, active site returns to almost complementary shape

Question 5

pH effects on enzyme activity

Answer 5

pH increases to optimum, increases enzyme activity
pH increases/decreases far away from optimum, decreasing enzyme activity to denaturation
Interaction of high concentrations of H+/OH- ions affect ionic bonds in active site tertiary structure, eventually irreversibly changes active site so substrate cannot bind, shapes no longer complementary

Question 6

Temperature effects on enzyme activity

Answer 6

Increasing enzyme activity up to optimum
Enzyme activity gradually decreases above optimum due to increased vibrations of tertiary structure bonds in active site -> irreversible change in specific 3D shape causes denaturation -> active site and substrate shape no longer complementary

Question 7

Effects of competitive inhibition

Answer 7

Inhibitor binds to active site as shape similar to some/all substrate
Overcome w/ inc. substrate conc

Question 8

Effects of non-competitive inhibition

Answer 8

Inhibitior binds to allosteric site as shape similar to some tertiary enzyme structure
Alters tertiary structure of active site, no longer complementary to substrate
No ESC formed
Cannot be overcome w/ inc. substrate conc.