(d,f) cofactors and enzyme inhibitions

What are cofactors and how do they work?

• Non-protein substances required for some enzymes to function
• Must be present and bound to the enzyme
• Can be inorganic ions or organic molecules
• Help the enzyme and substrate bind together
• Enable the reaction to occur

What are inorganic cofactors and give an example?

• Inorganic ions or molecules
• Help enzyme and substrate bind together
• Do not directly participate in the reaction
• Not used up or changed in any way
• Example: chloride ions (Cl–) for amylase

What are coenzymes (Organic cofactors) and how do they function?

• Organic molecules

• Participate in enzyme-controlled reactions

• Are chemically changed during the reaction

• Act like a second substrate (but not called one)

• Act as carriers as they Carry chemical groups between enzymes

• Continuously recycled during this process

How are coenzymes recycled in reactions?

• Coenzyme A is used by enzyme 1

• A is changed into B during the reaction

• Coenzyme B is then used by enzyme 2

• B is converted back into A

• Coenzyme is continuously recycled between reactions

What is the relationship between vitamins and coenzymes?

• Vitamins are often sources of coenzymes

• Example: NAD is derived from vitamin B3

What are prosthetic groups and give an example?

• Cofactors that are tightly/permanently bound to enzymes

• Often form part of the active site

• Example: zinc ions (Zn²⁺) in carbonic anhydrase

• Carbonic anhydrase is found in red blood cells

• Catalyses production of carbonic acid from CO₂ and water

What are enzyme inhibitors and what types are there?

• Molecules that bind to enzymes and reduce or stop activity

• Two types: competitive and non-competitive inhibitors

What are competitive inhibitors and how do they affect enzyme activity?

• Have a similar shape to the substrate (not identical)

• Compete with substrate for the active site

• Bind to active site but no reaction occurs

• Block substrate from binding

• Level of inhibition depends on relative concentrations of substrate and inhibitor

How does substrate concentration affect competitive inhibition?

• High inhibitor concentration → most active sites blocked → low rate

• High substrate concentration → substrate outcompetes inhibitor

• Rate of reaction increases as substrate concentration increases

• Increase occurs up to a point

What are non-competitive inhibitors and how do they affect enzymes?

• Bind to a different site (allosteric site), not the active site

• Do not compete with substrate

• Cause the active site to change shape

• Substrate can no longer fit into the active site

• Reaction is prevented

How does substrate concentration affect non-competitive inhibition?

• Increasing substrate concentration has little or no effect

• Active site remains altered and unusable

• Enzyme activity is still inhibited

What is the difference between reversible and irreversible inhibition?

• Reversible inhibition:

  • Inhibitor binds temporarily

  • Weak hydrogen or ionic bonds

  • Inhibitor can be removed

• Irreversible inhibition:

  • Inhibitor binds permanently

  • Strong covalent bonds

  • Cannot be easily removed

What is a covalent bond?

• A bond formed when two atoms share electrons