Coenzymes and Vitamins

Question 1

Cofactors

Answer 1

Assist in the catalytic process, but aren’t part of the enzyme itself

Question 2

Apoenzyme

Answer 2

Usually inactive, protein-only (enzyme)

Question 3

Holoenzyme

Answer 3

Apoenzyme + cofactor (active)

Question 4

Types of enzymes that require essential ions

Answer 4

Metal-activated enzymes (require or are stimulated by presence of metal ions- usually K, Ca, Mg)
Metalloenzymes (contain firmly bound metal ions in active sites- usually Zn, Fe, Cu, Co)

Question 5

Two types of coenzymes

Answer 5

Cosubstrates (substrates in reaction and are released from enzyme after reaction)
Prosthetic groups (remain bound to enzyme throughout reaction and must be regenerated to retain enzymatic activity)

Question 6

Obtaining coenzymes

Answer 6

Diet- humans can’t make them themselves

Question 7

Water-soluble vitamins

Answer 7

B vitamins, vitamin C, folate

Question 8

Fat-soluble vitamins

Answer 8

Vitamins A, D, E, K

Question 9

Adenosine triphosphate (ATP)

Answer 9

Cosubstrate

Phosphate transfer or energy

Question 10

S-adenosylmethionine (SAM)

Answer 10

Cosubstrate

Transfer of methyl groups

Question 11

Uridine diphosphate glucose

Answer 11

Cosubstrate

Glycosyl group donor

Question 12

Nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP+)

Answer 12

Cosubstrate
Vitamin source: niacin (vitamin B3)
Redox reactions involving 2 electron transfers

Question 13

Flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD)

Answer 13

Prosthetic group
Vitamin source: riboflavin (vitamin B2)
Redox reactions involving 1 and 2 electron transfers

Question 14

Coenzyme A (CoA)

Answer 14

Cosubstrate
Vitamin source: pantothenate (vitamin B3)
Transfer of acyl groups
Reactive center: -SH group

Question 15

Thiamine pyrophosphate

Answer 15

Prosthetic group
Vitamin source: thiamine (vitamin B1)
Transfer of 2-carbon fragments containing a carbonyl group

Question 16

Pyridoxal phosphate

Answer 16

Prosthetic group
Vitamin source: pyridoxine (vitamin B6)
Transfer of groups to and from amino acids

Question 17

Biotin

Answer 17

Prosthetic group

Carboxyl group transfers and carboxylation

Question 18

Avidin and streptavidin

Answer 18

Proteins with high affinity for biotin

Question 19

Tetrahydrofolate (THF)

Answer 19

Cosubstrate
Vitamin source: folate (vitamin B9)
Transfer of 1-carbon substituents

Question 20

Adenosylcobalamin

Answer 20

Prosthetic group
Vitamin source: cobalamin (vitamin B12)
Intramolecular rearrangements (hydrogen and functional group on adjacent carbon atoms switch places)

Question 21

Methylcobalamin

Answer 21

Prosthetic group
Vitamin source: cobalamin (vitamin B12)
Transfer of methyl groups

Question 22

Lipoamide

Answer 22

Prosthetic group

“Swinging arm” to transfer acyl groups between domains of multi-domain enzyme complexes

Question 23

Retinal

Answer 23

Prosthetic group
Vitamin A
Vision (conjugated pi system: absorption of light)

Question 24

Vitamin K

Answer 24

Prosthetic group

Synthesis of proteins involved in blood coagulation

Question 25

Ubiquinone (Q)

Answer 25

Cosubstrate

Lipid-soluble electron carrier

Question 26

Vitamin D

Answer 26

Hormone that controls Ca+2 intestinal absorption and bone desorption
Formed in skin upon exposure to sunlight (D3 only)

Question 27

Vitamin E

Answer 27

Radical and oxygen scavenger