Enzymes

Question 1

properties of enzymes

Answer 1

• biological catalyst –> speed up rate of reaction by lowering activation energy of the reaction and. are chemically unaltered at the end of the reaction and thus can be reused, and are effective in small amounts
• globular proteins, each with an active site with specific 3D conformation that is complementary in shape and charge to the specific substrate
• soluble in water, they are globular proteins with most of their hydrophilic amino acids on their external surface and most of the hydrophobic amino acids buried in the interior

Question 2

2 models that explain why enzymes are highly specific

Answer 2

1. lock and key hypothesis
   - enzyme active site is complementary in shape and charge to the substrate
   - when enzyme and substrate collide in the correct orientation, it forms an enzyme-substrate complex
   - catalysis will occur, products will no longer be complementary to the active site and leave
2. induced fit hypothesis
   - enzyme active site has a specific shape and charge complementary to the substrate
   - when substrate binds to the active site, it induces a conformational change of the active site to have a more precise fit for the substrate

Question 3

amino acid residues that make up the eznyme

Answer 3

1. contact residues: helps to position the substrate in the correct orientation via weak interactions
2. catalytic residues: have specific R groups which weakens the covalent bonds within the substate molecule, catalyse conversion of substrate to product
3. structural residues: hold the enzyme active site in its specific shape

Question 4

enzymes lower activation energy through:

Answer 4

• proximity effects: temporary binding of substrate in close proximity in the enzyme active site
• orientation effects: substrates are held by enzymes in their active sites in an orientation the bonds in substrates are exposed to chemical attack
• strain effects: slight distortion of substrates when they bind to active site, strains bonds in substrate

Question 5

Competitive inhibitors

Answer 5

• inhibitor is complementary to active site, it competes with substrate for active site of enzyme as they are structurally similar, reduces the availability of active sites for substrate binding, rate of reaction decreases
• at high substrate conc, effect of inhibition can be overcome, higher proportion of substrate molecules compared to. the inhibitor can effectively outcompete the inhibitor, hence Vmax can be reached

Question 6

Non-competitive inhibition

Answer 6

• inhibitor does not have a complementary shape. to active site, binds to site other than active site, resulting in a conformational change of the active site, hence substrate can no longer bind to active site, rate of reaction decreases
• inhibitor effectively decreases the available enzyme conc, as it forms an inactive enzyme-inhibitor complex, hence effects of inhibition cannot be overcome

Question 7

allosteric inhibition

Answer 7

• multimeric enzyme with multiple active sites and allosteric sites
• inhibitor binds to allosteric site of the enzyme, this results in a conformational change in enzyme
• binding of inhibitor stabilises the enzyme in a inactive state, binding of activator stabilises enzyme to an active state
• substrate binding stabilized the enzyme in the active conformation and opposes the effect of the inhibitor, this allows Vmax to be reached at high substrate concentrations.
• binding of substrate in allosteric enzymes exhibit cooperativity binding of a substate t the first subunit, changes the conformation of the other subunits such that it is easier to accept subsequent substrates