Lecture 7: Enzymes 1

Question 1

2 types of enzymes and names

Answer 1

Apoenzyme : completely protein and fully active

Holoenzyme: made of protein but requires associated non protein component in order to show catalytic activity.

Question 2

What are the different types of non protein components that bind to enzymes

Answer 2

Cofactor: binds and disassociates during the catalytic cycle (eg. metal ions)
Coenzymes: organic cofactor (eg vitamins)
Prosthetic group: tightly bound that doesn’t dissociate from enzyme

Question 3

Describe the specificity of enzymes

Answer 3

Enzymes can be very specific or promiscuous- accepting many similar substances that aren’t metabolised as well. This is a feature of redundancy, resilience and adaptability in biological systems which can help another enzyme take over a job if needed.

Question 4

Describe the 3 ways of regulation of enzymes

Answer 4

• Proenzymes can undergo proteolysis as one way on switch and proteolytic breakdown as off.
• transient covalent modification (eg. phosphorylation) which is a two way on and off switch
• Allostery: graded response to either substrate or other non covalently bonded regulatory molecules

Question 5

How do enzymes make product faster?

Answer 5

They lower the energy change required for the substrate to reach transition state (Ea) by forming a substrate enzyme complex that has weak bonds (H and hydrophobic) between enzyme and substrate.

Question 6

Do enzymes affect the overall free energy change in a reaction? what does this mean for the amount of product produced and how does it affect equilibrium.

Answer 6

Don’t affect change in G, so product is made faster, but they cannot make more product. The rate at which equilibrium is reached is sped up, but the position of equilibrium is not changed.

Question 7

When is the enzyme most tightly bound to substrate

Answer 7

when substrate is in transition state

Question 8

What are the 3 models of substrate recognition

Answer 8

lock and key= complementarity of character
induced fit= substrate causes enzyme conformational change
conformational selection= substrate chooses correct pre existing conformation of enzyme

Question 9

What are the other amino acids in an enzyme important for when the active site is only a small amount of amino acids

Answer 9

1. They position the active site amino acids for correct spatial orientation (sometimes unfavourable)
2. Provide the correct microenvironment for active site amino acid groups-> ionisable
3. Provide other sites for recognition and control purposes (allostery)