Lecture 8

Question 1

what is an apoenzyme?

Answer 1

an enzyme lacking a cofactor

Question 2

what is a holoenzyme?

Answer 2

an enzyme with its cofactors

Question 3

what is a cofactor?

Answer 3

• co-catalyst required for enzyme activity

Question 4

what is a coenzyme?

Answer 4

• an organic substance, non-covalently linked to an enzyme

- carries electrons, atoms, or functional groups (coenzymes)= transferred in the overall reaction.

Question 5

what is a prosthetic group?

Answer 5

• non-dissociable, non-protein component covalently bound to the apoenzyme.

Question 6

what is Km, what does it indicate?

Answer 6

• michaelis constant
• equal to the concentration of substrate at half of VMax
• indicates the enzymes affinity for a substrate

Question 7

lower Km means?

Answer 7

higher enzyme affinity for substrate

Question 8

what is the hyperbolic equation (michaelis-menten equation)?

Answer 8

V = Vmax [S] / Km + [S]

• allows you to find the velocity of the reaction at any substrate concentration so long as you have Km and Vmax

Question 9

higher Km means?

Answer 9

lower enzyme affinity for substrate

Question 10

What is Kcat?

Answer 10

• turnover number

- measure of catalytic production of product under optimum conditions.

Question 11

what order is it when substrate concentration is less than Km?

Answer 11

first order (velocity of reaction is proportional to substrate concentration)

Question 12

what order is it when substrate concentration is greater than Km?

Answer 12

zeroth order (velocity of reaction is independent of substrate concentration [plateau] )

Question 13

what is the effect of competitive inhibition on Km and VMax?

Answer 13

• Km increases (enzyme loses affinity for substrate due to competitive inhibitor)
• Vmax stays the same (more substrate than inhibitor will overcome)

Question 14

what is the effect of noncompetitive inhibition on Km and Vmax?

Answer 14

• Km stays the same (enzyme still binds substrate)

- Vmax decreases since inhibitor binds enzyme-substrate complex

Question 15

what is the effect of uncompetitive inhibition on Km and Vmax

Answer 15

• Km decreases (enzyme gains affinity)

- Vmax decreases (enzyme-substrate complex is inhibited)

Question 16

(lineweaver-burk plot) slope equals?

Answer 16

Km/Vmax

Question 17

how do you derive lineweaver-burk plot equation?

Answer 17

take the reciprocal of michealis-menten equation and do some fuckin math until you get something that looks like y=mx+b

Question 18

what are the three distinct inputs for activation of protein kinase?

Answer 18

1) phosphorylation of a threonine side chain
2) dephosphorylation of a specific tyrosine side chain
3) cyclin binding

Question 19

what is a zymogen?

Answer 19

• an inactive enzyme - (proenzyme) secreted as a large molecule with its active site unexposed.
• requires activation by proteolytic cleavage

Question 20

what are the enzymes that indicate liver damage?

Answer 20

• alanine aminotransferase (ALT)

- aspartate aminotransferase (AST)

Question 21

what are the enzymes that indicate pancreatitis?

Answer 21

• amylase

- lipase

Question 22

what are the enzymes that indicate myocardial infarction?

Answer 22

• CK-MB (creatine kinase MB)

- cTnI (cardiac troponin I)

Question 23

what are isozymes?

Answer 23

• enzymes that differ in amino acid sequence but catalyze the same reactions.
• think isotope