Chapter 7: Coenzymes and Vitamins

Question 1

molecules required by enzymes for catalysis

Answer 1

cofactors

Question 2

what are the two families of cofactors?

Answer 2

1. essential ions

2. coenzymes

Question 3

• usually metal ions

- often the essential minerals in your diet - activator ions for enzymes

Answer 3

essential ions

Question 4

• usually organic compounds

- act as group transfer agents - they accept and donate specific chemical groups

Answer 4

coenzymes

Question 5

what are the two classes of essential ions?

Answer 5

1. activator ions (loosely bound)

2. metal ions of metalloenzymes (tightly bound)

Question 6

what are the two classes of coenzymes?

Answer 6

1. cosubstrates (loosely bound)

2. prosthetic group (tightly bound)

Question 7

enzymes that require a cofactor but do not have one bound

Answer 7

apoenzymes (apoproteins)

Question 8

an enzyme together with the cofactor(s) required for activity

Answer 8

holoenzyme (holoprotein)

Question 9

what else can the term ‘holoenzyme’ be applied to?

Answer 9

• enzymes that contain multiple protein subunits

- proteins that transport small molecules

Question 10

what do more than a quarter of all enzymes require to achieve full catalytic activity?

Answer 10

metallic cations

Question 11

• either have an absolute requirement for added metal ions or are stimulated by the addition of metal ions
• the metal is not undergoing any changes

Answer 11

metal-activated enzymes

Question 12

• contain firmly bound metal ions at their active sites
• usually transition metals (often iron and zinc)
• metal often undergoes a change in redox state (involved in the mechanism)

Answer 12

metalloenzymes

Question 13

• coenzymes that act as susbtrate in enzyme-catalyzed reactions
• it is altered in the course of the reaction and dissociates from the active site
• subsequent reaction regenerates the original structure

Answer 13

cosubstrates

Question 14

• remain bound to the enzyme throughout the course of the reaction
• can be covalently or noncovalently bound to the apoenzyme
• must also be returned to its original form after catalysis

Answer 14

prosthetic groups

Question 15

what are the two broad classes of vitamins?

Answer 15

1. water soluble

2. lipid soluble

Question 16

required daily in small amounts because they are easily excreted in the urine and cellular stores are unstable

Answer 16

water soluble vitamins

Question 17

can be stored, usually in the liver, so excessive intake can be toxin (hypervitaminoses)

Answer 17

lipid soluble vitamins

Question 18

vitamin source: N/A
metabolic roles: transfer of phosphoryl or nucleotidyl groups
mechanistic role: cosubstrate

Answer 18

adenosine triphosphate (ATP)

Question 19

vitamin source: N/A
metabolic roles: transfer of methyl groups
mechanistic role: cosubstrate

Answer 19

S-Adenosylmethionine

Question 20

vitamin source: N/A
metabolic roles: transfer of glycosyl groups
mechanistic role: cosubstrate

Answer 20

uridine diphosphate glucose

Question 21

vitamin source: Niacin (B3)
metabolic roles: oxidation-reduction reactions involving two-electron transfers
mechanistic role: cosubstrate

Answer 21

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

Question 22

vitamin source: Riboflavin (B2)
metabolic roles: oxidation-reduction reactions involving two-electron transfers
mechanistic role: prosthetic group

Answer 22

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

Question 23

vitamin source: Pantothenate (B5)
metabolic roles: transfer of acyl groups
mechanistic role: cosubstrate

Answer 23

coenzyme A (CoA)

Question 24

vitamin source: Thiamine (B1)
metabolic roles: transfer of multi-carbon fragments containing a carbonyl group
mechanistic role: prosthetic group

Answer 24

thiamine pyrophosphate (TPP)

Question 25

vitamin source: Pyridoxine (B6)
metabolic roles: transfer of groups to and from amino acids
mechanistic role: prosthetic group

Answer 25

Pyridoxal phosphate (PLP)

Question 26

vitamin source: Biotin (B7)
metabolic roles: ATP-dependent carboxylation of substrates or carboxyl-group transfer between substrates
mechanistic role: prosthetic group

Answer 26

Biotin

Question 27

vitamin source: Folate
metabolic roles: transfer of one-carbon substituents, especially formyl and hydroxymethyl groups; provides the methyl group for thymine in DNA
mechanistic role: cosubstrate

Answer 27

Tetrahydrofolate

Question 28

vitamin source: Cobalamin (B12)
metabolic roles: intramolecular rearrangements, transfer of methyl groups
mechanistic role: prosthetic group

Answer 28

Cobalamin

Question 29

vitamin source: N/A
metabolic roles: oxidation of a hydroxyalkyl group from TPP and subsequent transfer as an acyl group
mechanistic role: prosthetic group

Answer 29

Lipoamide

Question 30

vitamin source: vitamin A
metabolic roles: vision
mechanistic role: prosthetic group

Answer 30

Retinal

Question 31

vitamin source: vitamin K
metabolic roles: carboxylation of some glutamate residues
mechanistic role: prosthetic group

Answer 31

Vitamin K

Question 32

vitamin source: N/A
metabolic roles: lipid-soluble electron carrier
mechanistic role: cosubstrate

Answer 32

Ubiquinone (Q)

Question 33

vitamin source: N/A
metabolic roles: electron transfer
mechanistic role: prosthetic group

Answer 33

Heme group