L12-13

Question 1

PKU is?

Answer 1

Deficiency in Phe hydroxylase - which breaks down Phe so that it can convert to Tyr

Question 2

Eg of enzyme cofactors?

Answer 2

Mg2+, K+

Question 3

Eg of coenzymes?

Answer 3

Vitamins - derived from diet that carry functional group

Question 4

What enzyme couples the phosphorylation of glucose and the hydrolysis of ATP?

Answer 4

Hexokinase

Question 5

What is binding free energy (Delta GB)?

Answer 5

The difference between the activation energies of the uncatalysed and catalysed reactions

Question 6

Enzymes reduce the AE of _ at the transition state

Answer 6

S

Question 7

What is delta G cat?

Answer 7

The net of the negative delta Gb and the positive delta G uncat

Question 8

Enzymes do not affect (2)

Answer 8

• Free E change for the S P reaction

- Equil constant Keq

Question 9

How is enzyme kinetics studied?

Answer 9

By determining V0 = V as t approaches zero - before S has had time to decrease

Question 10

Why might an enzyme’s rate of reaction decrease over time? (3)

Answer 10

1) Feedback inhibition (S is depleted by conversion to product where P builds up and inhibits reaction)
2) Reversible reaction (Too much P increases backwards reaction)
3) Enzyme unstable (denatures)

Question 11

Steady state for ES means that

Answer 11

The rate of formation of ES = the rate of removal of ES

Question 12

Difference between KD and KM

Answer 12

KM is defined in terms of steady-state conc not equil conc

Question 13

What is KM?

Answer 13

[E][S]/[ES] = (k2 + k-1)/k1

Question 14

What is Michaelis-Menten equation?

Answer 14

V0 = Vmax [S]/(km +[S])

When S&raquo_space; KM; V0 = Vmax
When S = KM; V0 = 1/2 Vmax

Question 15

Km is an indication of?

Answer 15

Affinity of the enzyme for S

Question 16

A low Km corresponds to a ___ affinity

Answer 16

high

Question 17

K2/kcat/the turnover number is?

Answer 17

The number of molecules of substrate converted to product per unit time per enzyme molecule saturated with substrate.

It is also the rate constant for the rate-limiting step.

Question 18

Competitive inhibition, how is Vmax and Km affected?

Answer 18

Vmax stays the same, Km increases

Question 19

Uncompetitive inhibition, how is Vmax and Km affected?

Answer 19

Both decreases.

Question 20

2 features of uncompetitive inhibition that is different to competitive.

Answer 20

Binds only after ES complex is formed and binds at allosteric site

Question 21

Does the modulator bind to R or C?

Answer 21

R. Substrate binds to C (catalytic subunit)

Question 22

ATCase, what is the activator and what is the inhibitor?

Answer 22

ATP is the activator. CTP is the inhibitor.

Question 23

ATCase, describe the catalytic and regulatory subunits.

Answer 23

C- 2 trimeric complexes

R- 3 dimeric compleses

Question 24

Do isolated catalytic subunits display allosteric enzymes kinetics or M-M kinetics?

Answer 24

M-M kinetics

Question 25

Are isolated regulatory subunits catalytically active? Do they still bind ATP and CTP?

Answer 25

No, Yes

Question 26

Are isolated catalytic subunits catalytically active? Do they still bind ATP and CTP?

Answer 26

Yes, No

Question 27

a-chymotrypsin, 2 phases of hydrolysis

Answer 27

1) Acylation of a Ser residue to form an acyl enzyme intermediate 2) Deacylation to return the enzyme to its original form

Question 28

a-chymotrypsin, catalytic triad

Answer 28

Asp102, His57, Ser195