SFP9: Regulation Of Enzyme Activity

Question 1

What are the slow enzyme regulatory strategies?

Answer 1

Amount of enzyme present

Isoenzymes (i.e. control of expression patterns)

Question 2

What are fast enzyme regulatory strategies?

Answer 2

• Allosteric control
• Proteolytic activation
• Covalent modification

Question 3

What regulatory strategies are gross/course control?

Answer 3

Control of protein expression and destruction

Location (compartmentalisation)

Question 4

What regulatory strategies are fine control?

Answer 4

Proteolytic activation
Allosteric control
Covalent modification (phosphorylation)

Question 5

What is proteolytic activation?

Answer 5

Enzyme is inactive until activated by cleavage of one or a few specific peptide bonds

Activation is not reversible

Question 6

Why are digestive enzymes a good example or proteolytic activation?

Answer 6

When they’re produced you dont want them to start digesting the tissues that produced them, want them to stay inactive until the site of requirement

Question 7

Explain activation of chymotrypsin by proteolytic activation

Answer 7

Inactive form chymotrypsinogen is produced by the pancreas
Activated when peptide bond between Arg-15 and Ile-16 is cleaved by trypsin
Resulting pi-chymotrypsin cleaves other pi-chymotrypsin molecules to form alpha-chymotrypsin
The 3 peptide chains are produced and held together by inter chain disulphide bonds

Question 8

What is allosteric control?

Answer 8

When activity is controlled by binding of small molecules at regulatory sites distant to the active site

Question 9

Is allosteric control positive or negative regulation?

Answer 9

Negative, a product produced late in a reaction pathway inhibits an enzyme that acts earlier in the pathway

Question 10

What is an example of an allosterically controlled enzyme?

Answer 10

Aspartate transcarbamoylase
- catalyse first step in pyramiding biosynthesis
Final product (CTP) inhibits first step
ATCase is inhibited by CTP
CTP is an allosteric inhibitor

Question 11

What is covalent modification?

Answer 11

Regulatory groups being attached to the enzyme via a covalent bond

Question 12

What is phosphorylation covalent modification?

Answer 12

When protein kinases catalyse the transfer of phosphate groups to proteins (donor molecule - ATP)

Question 13

Is phosphorylation reversible or irreversible?

Answer 13

Reversible

Question 14

What 3 inputs do cyclin-dependent kinases control the timing of the cell cycle with?

Answer 14

1) kinase
2) phosphatase
3) cyclin
CDK is like a microchip which relays a signal only when all 3 inputs are met