Deck 7: Coenzymes and Vitamins

Question 1

The reactive center of coenzyme A is

A) ADP.
B) pantothenate.
C) b-alanine.
D) 2-mercaptoethylamine.
E) serine.

Answer 1

2-mercaptoethylamine.

Question 2

The role of zinc in the mechanisms of carbonic anhydrase is to

A) maintain the configuration of the holoenzyme.
B) bind to three histidine residues.
C) produce a nucleophilic attack on the substrate.
D) promote ionization of bound water.
E) produce an electrophilic attack on the substrate.

Answer 2

promote ionization of bound water.

Question 3

Because coenzymes are specific for the chemical groups that they accept and donate, they are referred to as

A) cofactors.
B) reactive centers.
C) activator ions.
D) group-transfer reagents.
E) All of the above

Answer 3

group-transfer reagents.

Question 4

Which coenzyme is likely involved in the reaction shown below?

A) TPP
B) biotin
C) coenzyme A
D) FMN

Question 5

Which coenzyme is composed of a 2-mercaptoethylamine unit, the vitamin pantothenate and an ADP moiety?

A) NADPH
B) biotin
C) coenzyme A
D) ubiquinone

Question 6

Active holoenzymes are formed from in the presence of .

A) cofactors; proteins
B) proteins; cofactors
C) apoenzymes; cofactors
D) apoenzymes; proteins
E) apoenzymes; inactive holoenzymes

Question 7

The products) of lactate dehydrogenase under anaerobic conditions is are)

A) pyruvic acid.
B) NAD⁺.
C) NADH.
D) A and B
E) A and C

Question 8

Which does not return to its original form after each catalysis?

A) prosthetic groups
B) cosubstrates
C) metalloenzyme
D) None of the above. They all return to their original forms.

Question 9

When NAD⁺ is reduced, the UV absorbance at 340 nm

A) decreases.
B) increases.
C) stays the same.
D) decreases, then increases.
E) increases, then decreases.

Question 10

Vitamin C is a vitamin but not a coenzyme because it

A) does not bind to proteins.
B) is a prosthetic group.
C) is a reducing agent during hydroxylation of collagen.
D) is not required in human diets.

Question 11

The ʺ+ʺ sign in NAD⁺ indicates that

A) this is the reduced form of the coenzyme.
B) the nitrogen atom has a positive charge.
C) the entire molecule is positively charged.
D) it can bind to negatively charged proteins only.

Question 12

What is the role of the magnesium ion in kinases that require the magnesium-ATP complex to donate phosphoryl groups?

A) maintain the configuration of the holoenzyme
B) shield the charged phosphate groups of ATP
C) produce an electrophilic attack on the substrate
D) promote ionization of bound water
E) produce ionization of the substrate to be phosphorylated

Question 13

Unlike NADH and NADPH, FAD and FADH

A) donate one electron at a time.
B) donate one or two electrons at a time.
C) do not become positively charged.
D) A and C
E) B and C

Question 14

S-adenosylmethionine SAM) is formed from the amino acid methionine so that

A) methyl groups can be formed.
B) it can react with nucleophilic acceptors.
C) it can donate methyl groups in many biosynthetic reactions.
D) All of the above
E) B and C

Question 15

An ion commonly found in metalloenzymes and which can undergo reversible oxidation and reduction is

A) Ca⁺⁺.
B) Mg⁺⁺.
C) S^-.
D) Fe⁺⁺.
E) All of the above

Question 16

A nucleotide-sugar coenzyme involved in carbohydrate metabolism UDP-glucose) is formed when UTP reacts with a glucose molecule. More UTP is made available for additional reactions by the transfer of a phosphate group from

A) another carbohydrate.
B) ATP.
C) ADP.
D) UTP.
E) UDP.

Question 17

Two-electron transfer reactions can be linked to one-electron transfer reactions by

A) formation of semiquinones.
B) a [Fe-S] cluster.
C) NADH and NADPH.
D) B and C
E) A and C

Question 18

Ca⁺⁺ or Mg⁺⁺ are most likely to be part of , while Zn⁺⁺ or Fe⁺⁺ are present in .

A) metal-activated enzymes; metalloenzymes
B) metalloenzymes; metal-activated enzymes
C) cofactors; coenzymes
D) coenzymes; cofactors
E) apoenzymes; holoenzymes

Question 19

Acyl-group-transfer reactions often involve which coenzyme?

A) Coenzyme A
B) NAD⁺
C) cytochrome c
D) All of the above

Question 20

NAD and NADP dependent dehydrogenases catalyze substrates by transferring to C-4 of NAD⁺ and NADP⁺.

A) one electron
B) two electrons
C) one electron and one proton
D) two electrons and one proton
E) two electrons and two protons

Question 21

Which atom is the reactive center on biotin?

A) Arrow 1
B) Arrow 2
C) Arrow 3
D) Arrow 4

Question 22

Which amino acid can form a covalent bond to the coenzyme pyridoxal phosphate?

A) aspartate
B) cysteine
C) lysine
D) serine

Question 23

Which functional group is shown below?

A) Schiff base
B) secondary amine
C) amide
D) peptide bond

Question 24

Pyridoxal phosphate is involved in which type of reaction?

A) oxidation of pyruvate
B) production of new amino acids by transamination
C) phosphate-transfer to produce ATP from ADP
D) the regeneration of methionine from homocysteine

Question 25

We use the term tetrahydrofolate to designate a family of related compounds. What is the main difference between members of this family?

A) degree of protonation
B) number of methyl groups on the heterocylic rings
C) number of phosphate groups
D) length of the polyglutamate tail group

Question 26

Why has dihydrofolate reductase been identified as a potential target for chemotherapy in the treatment of cancer?

A) It is a hormone that is a primary control agent of the rate of mitosis.
B) It is a DNA binding protein that activates a cancer oncogene.
C) It is essential in DNA synthesis. Cell division will not occur without it.
D) It selectively binds to a receptor on the surface of cancer cells and inactivates them.

Question 27

The degradation of aspartic acid to oxaloacetic acid and NH₄⁺ is catalyzed by an enzyme with as its prosthetic group.

A) thiamine
B) biotin
C) pyridoxal phosphate
D) vitamin B₁₂

Question 28

Which substance would make a good ligand for biotin on the matrix of an affinity chromatography column?

A) ubiquinone
B) avidin
C) oxaloacetate
D) any molecule with an -SH group

Question 29

The structure shown below is which coenzyme?

A) QH₂
B) Vitamin B₁₂
C) Biotin
D) Thiamine pyrophosphate

Question 30

Which coenzyme links to a lysine residue in a proteinʹs active site?

A) biotin
B) lipoic acid lipoamide)
C) pyridoxal phosphate
D) biotin and pyridoxal phosphate only
E) All three; biotin, lipoic acid and pyridoxal phosphate

Question 31

Which structure is not a part of folate?

A) porphyrin ring
B) p-aminobenzoic acid
C) pterin
D) glutamate residues

Question 32

Raw egg white contains a protein called avidin. What happens if you ingest raw egg whites?

A) Avidin helps to build muscle tissue.
B) Avidin is the main protein involved in salmonella poisoning.
C) Avidin binds onto the coenzyme biotin and interferes with its absorption.
D) Avidin, also called intrinsic factor, helps transport cobalamin into the cells of the small intestine.

Question 33

Which in not a lipid-soluble vitamin?

A) A
B) C
C) E
D) K

Question 34

Which type of atom is involved in the reactive center of lipoamide?

A) sulfur
B) nitrogen
C) phosphorous
D) oxygen

Question 35

What kind of reaction is most important for the reactive center of lipoamide?

A) oxidation of a carbonyl group
B) reduction of a disulfide bond
C) formation of a Schiff base
D) a cis-trans configurational change about a disulfide bond

Question 36

TPP is a/an of yeast pyruvate decarboxylase.

A) cosubstrate
B) intrinsic factor
C) metalloenzyme
D) prosthetic group

Question 37

Enzymes with vitamin B₆ as the prosthetic group catalyze a variety of reactions involving

A) lipids.
B) sugars.
C) amino acids.
D) other vitamins.

Question 38

Which characterizes cobalamin?

A) participates in the conversion of homocysteine to methionine
B) contains a corrin ring prosthetic group
C) requires a glycoprotein for its absorption
D) All of the above

Question 39

Which statement is false about 5,6,7,8-tetrahydrobiopterin?

A) It is required by the enzyme that catalyzes the synthesis of nitric oxide from arginine.
B) It is synthesized by animals and other organisms.
C) It is used in the transfer of phosphate groups during DNA synthesis.
D) It is a reducing agent in the conversion of phenylalanine to tyrosine.

Question 40

Which vitamin is shown below?

A) vitamin C
B) thiamin vitamin B₁)
C) cobalamin vitamin B₁₂)
D) folate

Question 41

What is the prosthetic group of the retinal vision protein rhodopsin?

A) retinol
B) retinal
C) retinoic acid
D) β-carotene

Question 42

Lipid vitamins such as A, D, E, and K are stored by animal cells, so excessive daily intake may be toxic.

Question 43

In which type of reactions does Q participate?

A) One electron transfers only.
B) One or two electron transfers.
C) Hydride ion transfers.
D) Acetyl group transfers.

Question 44

Which is the strongest oxidizing agent?

A) ubiquinone
B) NAD⁺
C) FMN
D) Vitamin K

Question 45

Which structure in shown?

A) retinol
B) retinal
C) retinoic acid
D) β-carotene

Question 46

Vitamin D helps control the utilization of which ion?

A) Mg²⁺
B) Ca²⁺
C) Fe²⁺
D) Co²⁺

Question 47

Vitamin C is a coenzyme during the hydroxylation of collagen.

Question 48

Metalloenzymes contain metal ions which are bound tightly to the protein and can attract electrons.

Question 49

Another name for α-tocopherol is vitamin .

A) A
B) B₁₂
C) C
D) D
E) E

Question 50

Mammalian cells can synthesize all needed coenzymes from simple precursors.

Question 51

Rickets in children and osteomalacia in adults is caused by a lack of .

A) thiamin
B) hemoglobin
C) vitamin D
D) vitamin B₁₂

Question 52

Minerals which are cofactors may be reversibly bound and are then usually directly involved in catalytic reactions.

Question 53

Organic compounds are coenzymes and cofactors while inorganic ions are cofactors only.

Question 54

Which statement is false about plastoquinone?

A) It is water soluble.
B) It is important in photosynthetic electron transport.
C) It contains five-carbon isoprenoid units.
D) It can be converted to a semiquinone form.

Question 55

Vitamin K is important in the .

A) synthesis of collagen
B) absorption of Ca²⁺
C) coagulation of blood clotting)
D) scavenging of oxygen and free radicals

Question 56

Metal-activated enzymes may require a metal ion or simply be stimulated in the presence of the ion.

Question 57

Which are common protein coenzymes?

A) cytochromes
B) phylloquinones
C) tetrahydrofolates
D) α-tocopherols

Question 58

All enzymes require metallic cations to achieve full catalytic activity.

Question 59

Vitamin deficiency diseases are a result of the lack of formation of certain coenzymes.

Question 60

Protein catalysts rely exclusively on the amino acid residues for reactivity at the sites of action.

Question 61

Match each of the following vitamins with an associate nutritional deficiency disease.
Ascorbate

Question 62

Structures of several dehydrogenases indicate that many possess one or more similar NAD or NADP-binding structures consisting of babab units in Rossman folds.

Question 63

Lack of thiamine vitamin B₁) leads to the disease beriberi.

Question 64

Lysine can join the prosthetic group biotin to an enzyme via an amide link at the ε-amino group.

Question 65

Match each of the following vitamins with an associate nutritional deficiency disease.
Folate

Question 66

The oxidized forms of cytochromes c absorbs more strongly than the reduced form at the Soret band near 400 nm.

Question 67

The reactive center of CoA is the -NH₃⁺ group.

Question 68

Pernicious anemia is caused by a deficiency in biotin.

Question 69

Tetrahydrofolate is a more oxidized form of the vitamin folate from which it is derived.

Question 70

An internal aldimine forms when PLP is covalently bound to its enzyme.

Question 71

Ubiquinone and plastoquinone transport electrons in membranes.

Question 72

Match each of the following vitamins with an associate nutritional deficiency disease.
Cobalamin B₁₂)

Question 73

Vitamin E is formed non-enzymatically in sun-exposed skin.

Question 74

Match each of the following vitamins with an associate nutritional deficiency disease.
Thiamine B₁)

Question 75

Vitamin A is produced from b-carotene by a condensation reaction.

Question 76

There is little risk in taking megadoses of vitamin A since excess will tend to simply be excreted in the urine.

Question 77

Cobalamin is synthesized by most organisms from simple precursors and does not need to be in the diet.

Question 78

The corrin ring is very similar to a heme, but the corrin ring containing vitamin B₁₂ has a cobalt ion rather than an iron ion as in heme.

Question 79

Another name for vitamin K is phylloquinone.

Question 80

Match each of the following vitamins with an associate nutritional deficiency disease.
Biotin