Enzymes

Question 1

What are enzyme inhibitors?

Answer 1

A molecule that inhibits the action of specific enzyme(s) (reduces enzyme activity & rate of reaction). They are categorized into 2 main groups: competitive inhibitors, non-competitive inhibitors.

Question 2

What is a competitive inhibitor?

Answer 2

• Structurally similar to the substrate of the enzyme that it inhibits (in terms of shape, size, charge, orientation)
• Bind to the active site of the enzyme, competes with the substrate for the active site (reduce no. of active sites available for substrates to bind)
• When it binds to the active site, the inhibitor remains unreactive

Question 3

What is a non-competitive inhibitor?

Answer 3

• Not structurally similar to the substrate of the enzyme that they inhibit (in terms of shape, size, charge, orientation)
• Binds at a site away from the active site (does not compete directly with the substrate for the active site)
• Interaction alters the specific 3-dimensional conformation of the enzyme molecule such that the active site is distorted and no longer complementary to substrate, thus not able to bind to the substrate properly or the substrate can still bind to active site but the enzyme is not able to catalyse the conversion of substrate to product
• Inhibitor remains unreactive

Question 4

What is a holoenzyme?

Answer 4

A complete, catalytically active enzyme together with its bound coenzyme and/or metal ions.

Question 5

What is the mode of action of enzymes?

Answer 5

1. Formation of enzyme substrate complex
   - enzyme and substrate collide in correct orientation
   - effective collision: substrate binds to active site of enzyme
   - enzyme-substrate complex formed
2. Amino acid residues
   - substrate molecules held in active site by non-covalent bonds such as hydrogen and ionic bonds between R groups of binding amino acids and the substrate molecules
   - R groups of catalytic amino acid residues at the active site catalyse the conversion of subrace to product
3. Release of product molecules
   - alteration in chemical confirmation causes active site to no longer be complementary to the active site structure
4. Enzyme can be reused
   - enzyme active site is free for the binding of another substrate molecule