Coenzymes + Cofactors

Question 1

deltaG’o

Answer 1

the difference between the free energy (G) of the substrates and the products

Question 2

A catalyst cannot effect the position and direction of equilibrium. True or false?

Answer 2

True

Question 3

Enzymes + activation energy

Answer 3

~ enzymes enhance the rate of reaction by lowering the activation energy

Question 4

E + S =….

Answer 4

E + S ES EP E + P
~ numerous weak interactions between
E & S (enzyme and substrate) are optimised in the transition state

Question 5

Cofactor

Answer 5

a non-protein component required by enzymes

Question 6

Coenzymes

Answer 6

organic cofactors

Question 7

Co-substrates

Answer 7

coenzymes that are loosely associated with their enzyme

e.g. NAD/NADP

Question 8

Prosthetic groups

Answer 8

tightly associated cofactors

e.g. flavin group

Question 9

Metal cations

Answer 9

~ type of cofactor
~ multiple oxidation sates are often important
e.g. Na+ Mg2+

Question 10

Co-enzymes participate in…

Answer 10

group transfer reactions
~ transient carriers of info
~ activated carrier

Question 11

Apoprotein/apoenzyme

Answer 11

protein/enzyme without its tightly associated cofactor

Question 12

Holoprotein/holoenzyme

Answer 12

protein/enzyme bound to its tightly associated cofactor = active enzyme

Question 13

List co-enzymes and the vitamins they are derived from.

Answer 13

NAD+/NADP = Vitamin B3
FMN/FAD = Vitamin B2
Coenzyme A = Vitamin B5
Pyridoxal phosphate = Vitamin B6

Question 14

NAD stands for…

Answer 14

nicotinamide adenine dinucleotide

Question 15

NAD + NADP (4)

Answer 15

~ function in 2e- transfer reactions
~ a.k.a. pyridine nucleotides
~ contain a nicotinamide ring
~ can also accept H- = 1 proton and 2e-

Question 16

NAD+ function

Answer 16

~ oxidation of alcohol and aldehydes

~ alcohol/aldehyde dehydrogenase

Question 17

Transdeamination

Answer 17

~ catalysed by glutamate dehydrogenase
~ uses NADH/NADPH as coenzymes
~ rare example

Question 18

High levels of NAD/NADH or NADP/NADPH favours…

Answer 18

hydride transfer from substrate

Question 19

How do enzymes lower the activation energy?

Answer 19

~ substrate binding = decrease in freedom of movement/rotation
~ they distort their substrate towards the transition state
~ the multiple weak ads between substrate and active site can offset/pay activation energy

Question 20

Flavin group

Answer 20

e.g. FAD/FMN
~ prosthetic group
~ participate in e- tranfers
~ reactive part = isoalloxazine ring

Question 21

Coenzyme A

Answer 21

active carrier of acetyl and acyl groups

Question 22

The Rossman fold

Answer 22

a classic nucleotide binding motif found in all NAD(P)-dependent dehydrogenases and used to bind the cofactor