Session 3

Question 1

What does a low Km value mean?

Answer 1

A high affinity of the enzyme for the substrate

Question 2

What will happen to Km and Vmax during competitive inhibition?

Answer 2

Km increases, Vmax unaffected

Question 3

What will happen to Km and Vmax during non-competitive inhibition

Answer 3

Km unaffected, Vmax decreases

Question 4

What is an irreversible inhibitor?

Answer 4

A substance which forms a covalent bond with the enzyme

Question 5

Define isoenzymes

Answer 5

Enzymes that catalyse the same reaction but have different amino acid sequences

Question 6

Define T state and R state of enzymes

Answer 6

T state- low affinity

R state- high affinity

Question 7

What is the action of protein kinases?

Answer 7

Transfer the gamma phosphate of ATP to the hydroxyl group of Serine, threonine, tyrosine

Question 8

What is the action of protein phosphatases?

Answer 8

Reverse the effects of kinases by catalysing the hydrolytic removal of phosphoryl groups from proteins

Question 9

Define proteolytic activation

Answer 9

The irreversible cleaving of a peptide bond in zymogens or proenzymes into order to activate them

Question 10

How does cleaving a protein activate a zymogen?

Answer 10

N-terminus peptide is cleaved off, newly formed n-terminus rotates towards active site, inducing conformational changes that create the functional active site