Deck 7: Coenzymes and Vitamins

Question 1

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.

Answer 1

formation of semiquinones.

Question 2

The product(s)of lactate dehydrogenase under anaerobic conditions in the muscle is (are)

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

Answer 2

A and C.

Question 3

Unlike coenzymes that are prosthetic groups,________ are altered in the course of an enzyme reaction and dissociate from the active site.

A)isozymes
B)cosubstrates
C)metalloenzymes
D)holoenzymes

Answer 3

cosubstrates

Question 4

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.

Question 5

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.

Question 6

The "+" 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 7

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 8

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 9

ATP is involved in

A)transferring a phosphate group to other compounds.
B)forming S-adenosylmethionine.
C)transfer of its AMP moiety to another compound.
D)All of the above.
E)A and C only.

Question 10

The metal ions in metalloenzymes are firmly bound at the active site of the enzyme.The ion may be bound to side chains of amino acids or may be part of a ________ group such as those found in catalase and cytochromes.

A)sulfur clusters
B)phosphate
C)vitamin
D)heme

Question 11

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 12

Enzymes that have FAD or FMN as prosthetic groups are called

A)flavoenzymes.
B)flavoproteins.
C)Old Yellow Enzyme.
D)All of the above.
E)A and B only.

Question 13

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 14

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 15

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 16

Unlike NADH and NADPH,FAD and FADH₂

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 17

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 18

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 19

What structure is shown?

A)NADH
B)NAD+
C)FMN
D)FAD

Question 20

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 21

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 22

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 23

Which functional group is shown below?

A)Schiff base.
B)Secondary amine.
C)Amide.
D)Peptide bond.

Question 24

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 25

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 26

TPP is a(n)________ of yeast pyruvate decarboxylase.

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

Question 27

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

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

Question 28

The structure shown below is which coenzyme?

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

Question 29

Vitamin C is not a coenzyme but acts in cell metabolism as a

A)buffer.
B)source of glucose.
C)reducing agent.
D)key nutrient.

Question 30

Transaminases are PLP-dependent enzymes that

A)remove the alpha-amino group from amino acids.
B)convert pyruvate to lactate.
C)degrade heme groups.
D)donate electrons two at a time.

Question 31

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

A)Aspartate.
B)Cysteine.
C)Lysine.
D)Serine.
E)All of the above.

Question 32

Acyl-group-transfer reactions often involve which coenzyme?

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

Question 33

Which atom is the reactive center on biotin?

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

Question 34

What is another name for vitamin B1?

A)Biotin.
B)Thiamine.
C)Lipoamide.
D)Pyridoxal phosphate.

Question 35

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 36

Which coenzyme is likely involved in the reaction shown below?

A)TPP.
B)Biotin.
C)Coenzyme A.
D)FMN.

Question 37

Which would be an efficient method of purifying biotin?

A)Affinity chromatography on a column of immobilized avidin.
B)SDS-PAGE with avidin uniformly dispersed in the gel.
C)Precipitation of biotin using amylopectin.
D)Site-directed mutagenesis using avidin as the mutating agent.

Question 38

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 39

Which metabolic function depends on Coenzyme A?

A)Oxidation of fuel molecules.
B)Synthesis of DNA.
C)Synthesis of guanine.
D)Conversion of ATP to ADP.

Question 40

The reactive center of coenzyme A is

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

Question 41

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 42

Another name for α-tocopherol is vitamin ________.

A)A
B)B₁₂
C)C
D)D
E)E

Question 43

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 44

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 45

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 46

Which structure is not a part of folate?

A)Porphyrin ring.
B)P-aminobenzoic acid.
C)Pterin.
D)Glutamate residues.

Question 47

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 48

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

A)Sulfur.
B)Nitrogen.
C)Phosphorous.
D)Oxygen.

Question 49

Which coenzyme links to a lysine residue in a protein's 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 50

Which is the strongest oxidizing agent?

A)Ubiquinone.
B)NAD+.
C)FMN.
D)Vitamin K.

Question 51

Which structure in shown?

A)Retinol.
B)Retinal.
C)Retinoic acid.
D)β-carotene.

Question 52

Which vitamin is shown below?

A)Vitamin C.
B)Thiamin (vitamin B1).
C)cobalamin (vitamin B12).
D)folate.

Question 53

What is another name for vitamin B12?

A)Thiamine.
B)Tetrahydrofolate.
C)Cobalamin.
D)Biotin.

Question 54

Which is the largest B vitamin?

A)B1
B)B6
C)B8
D)B12

Question 55

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 56

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

A)Retinol.
B)Retinal.
C)Retinoic acid.
D)β-carotene.

Question 57

Which in not a lipid-soluble vitamin?

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

Question 58

Vitamin D helps control the utilization of which ion?

A)Mg²⁺
B)Ca²⁺
C)Fe²⁺
D)CO²⁺

Question 59

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 60

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

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

Question 61

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

Question 62

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

Question 63

All enzymes require metallic cations to achieve full catalytic activity.

Question 64

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

Question 65

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

Question 66

Which are common protein coenzymes?

A)Cytochromes.
B)Phylloquinones.
C)Tetrahydrofolates.
D)α-tocopherols .

Question 67

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 68

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

Question 69

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

Question 70

Pernicious anemia is caused by a deficiency in biotin.

Question 71

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

Question 72

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

Question 73

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

Question 74

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

Question 75

Mammalian cells can synthesize all needed coenzymes from simple precursors.

Question 76

Vitamin C is a coenzyme during the hydroxylation of collagen.

Question 77

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

Question 78

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

Question 79

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 80

Cytochromes are classified a,b or c based on

A)solubility.
B)The Soret band in absorption spectra.
C)The beta band in absorption spectra.
D)The alpha band in absorption spectra.