Deck 23: The Organic Chemistry of the Coenzymes, compounds Derived From Vitamins

Question 1

Identify all true statement(s).You may choose more than one answer.

A)NADH is oxidized to NAD⁺.
B)NADPH is oxidized to NADP⁺.
C)NADH is reduced to NAD⁺.
D)NADPH is reduced to NADP⁺.
E)NAD⁺ is oxidized to NADH.

Answer 1

NADH is oxidized to NAD⁺.
NADPH is oxidized to NADP⁺.

Question 2

List the four stages of catabolism and briefly explain the significance of each.

Answer 2

The first stage of catabolism is called digestion.In this stage,fats,carbohydrates,and proteins are hydrolyzed into fatty acids,monosaccharides,and amino acids respectively.The second stage is one in which these hydrolytic products are converted into compounds which can enter the citric acid cycle (acetyl-CoA,pyruvate,citric acid cycle intermediates).The third stage of catabolism is the citric acid cycle itself.For every acetyl-CoA that enters the cycle,two molecules of carbon dioxide are formed.The final stage of catabolism is called oxidative phosphorylation.Herein,every NADH that was formed in the earlier stages is converted into three ATPs.

Question 3

Explain what is meant by a nucleotide and give an example.

Answer 3

A nucleotide is composed of a heterocyclic molecule attached to the β-position of a phosphorylated ribose. Ex.NAD⁺ (nicotinamide adenine dinucleotide)is composed of two nucleotides linked together through their phosphate group.

Question 4

Can an NAD⁺/NADH dependent enzyme tell the difference between the pro-R hydrogen and pro-S hydrogen of a substrate? Explain.

Question 5

Explain why a cell typically maintains its [NAD⁺]/[NADH] ratio near 1000 while keeping its [NADP⁺]/[NADPH] ratio at about 0.01.

Question 6

Which of the following is/are coenzyme(s)formed from the vitamin niacin?

A)NAD⁺
B)NADP⁺
C)NADH
D)NADPH
E)all of the above

Question 7

How does NAD⁺ serve as a catalyst in oxidation reactions?

A)It accepts a hydride ion at the 4-position of its pyridinium ring.
B)It accepts a hydride ion at the amide carbonyl group at the 3-position.
C)It accepts a proton at the 4-position of its pyridinium ring.
D)It accepts a proton at the amide carbonyl group at the 3-position.
E)none of the above

Question 8

At what position of the pyridinium ring in the coenzyme below will oxidation-reduction reactions take place?

A)1
B)2
C)3
D)4
E)5

Question 9

Which of the following is not true about catabolic reactions?

A)Catabolic reactions require NAD⁺ for a coenzyme.
B)Catabolic reactions are most often oxidation reactions.
C)Catabolic reactions are most often reduction reactions.
D)Catabolic reactions require an oxidizing coenzyme.
E)Catabolic reactions break down complex molecules into simpler ones.

Question 10

Generally speaking,which of the following oxidation-reduction reactions utilize NAD⁺ and NADP⁺ as oxidation coenzymes?

A)alcohols oxidized to ketones
B)alcohols oxidized to aldehydes
C)alcohols oxidized to carboxylic acids
D)A and B
E)A,B,and C

Question 11

What structural feature of enzymes that catalyze redox reactions requires the presence of a coenzyme for reaction to occur?

Question 12

Which of the following statements regarding glycolysis is correct?

A)Glycolysis is another name for the Krebs cycle.
B)Disaccharides can enter glycolysis without being hydrolyzed.
C)Glycolysis occurs primarily in the fluid outside the cell.
D)Glycolysis is the series of reactions which produces 2 moles of pyruvate from each mole of D-glucose.
E)Glycolysis is the series of reactions which is responsible for the complete oxidation of pyruvate and acetyl-CoA to carbon dioxide.

Question 13

What are catabolic and anabolic reactions?

Question 14

Which of the following statements is true about metabolism?

A)reactions that living organisms carry out to obtain energy and to synthesize required compounds
B)reactions that organic chemists carry out to obtain energy and to synthesize required compounds
C)reactions that consist of catabolic and anabolic reactions
D)A and C
E)B and C

Question 15

All redox chemistry of the pyridine nucleotide coenzymes takes place at the ________-position of the pyridine ring.

Question 16

In a process known as oxidative phosphorylation,every NADH that is formed in carrying out oxidation reactions in the early stages of catabolism is converted into

A)three ATPs.
B)two ATPs.
C)four FADHs.
D)six acetyl-CoAs.
E)none of the above.

Question 17

What are the main structural and functional differences between NAD⁺/NADH and NADP⁺/NADPH?

Question 18

What is the major organic product of this oxidation-reduction reaction?

A)
B)
C)
D)
E)

Question 19

In which of the following classes of reactions is a coenzyme required?

A)oxidation reactions
B)two carbon transfer
C)acyl transfer
D)reduction reactions
E)A,B,and D

Question 20

Give the product for the following reaction.

A)
B)
C)
D)
E)

Question 21

Identify the true statement(s).You may choose more than one answer.

A)FAD is an oxidizing agent.
B)FADH₂ is an oxidizing agent.
C)FMNH₂ is a reducing agent.
D)NADH is an oxidizing agent.
E)NADPH is a reducing agent.

Question 22

Give the purpose of FAD and FMN.

Question 23

Give the product for the following reaction.

A)
B)
C)
D)
E)

Question 24

Which coenzyme is needed in the conversion of b-aspartate-semialdehyde to homoserine,a reduction reaction?

A)NADPH
B)biotin
C)PLP
D)lipoate
E)THF

Question 25

All water-soluble vitamins except vitamin ________ are precursors of coenzymes.

A)C
B)K
C)D
D)B₁
E)B₁₂

Question 26

Propose a mechanism for the following reaction.

Question 27

Which of the following vitamins is involved in the catalysis of an acyl transfer reaction?

A)vitamin B₁
B)folic acid
C)vitamin B₁₂
D)biotin
E)lipoic acid

Question 28

Which of the following is not needed for the pyruvate dehydrogenase system?

A)lipoate
B)coenzyme A
C)FAD
D)NAD⁺
E)biotin

Question 29

The thiazolium ring of ________ acts as electron sink when it participates in metabolic reactions.

A)TTP
B)CoASH
C)PLP
D)THF
E)FAD

Question 30

Pantothenic acid is used to form the coenzyme(s)

A)NAD⁺ and NADH.
B)FAD and FADH₂.
C)TTP.
D)CoASH.
E)THF.

Question 31

Which of the following substrates requires the coenzyme thiamine pyrophosphate (TPP)for catalyzing its decarboxylation reaction?

A)
B)
C)
D)
E)

Question 32

What are the products obtained from the reaction of NADH with FMN catalyzed by NADH dehydrogenase as shown below?

A)NAD⁺ + FMNH₂
B)NAD⁺ + FMNH
C)NAF + DHN
D)NAF + DNH₂
E)N₂A₂D₂ + FMNH₂

Question 33

Give the product of the following reaction.

A)
B)
C)
D)
E)

Question 34

Vitamin B₂ is used to form the coenzyme(s)

A)NAD⁺ and NADH.
B)FAD and FADH₂.
C)TTP.
D)CoASH.
E)THF.

Question 35

The common name of vitamin B₁ is

A)niacin.
B)riboflavin.
C)thiamine.
D)biotin.
E)panthothenate.

Question 36

At what position on the following coenzyme (FAD/FMN)will oxidation-reduction reactions take place?

A)6
B)2
C)3
D)4
E)5

Question 37

Which of the following is/are the coenzyme(s)formed from the vitamin thiamine (B₁)?

A)TPP
B)CoASH
C)PLP
D)THF
E)FAD

Question 38

Explain what is meant by a prosthetic group.Give an example.

Question 39

A deficiency of ________ results in megoblastic anemia.

A)folic acid
B)thiamine
C)niacin
D)riboflavin
E)vitamin D

Question 40

Identify the compound below.

A)coenzyme A
B)thiamine pyrophosphate
C)pyruvate
D)NADPH
E)tetrahydrofolate

Question 41

In addition to TPP,which of the following coenzymes is/are required to facilitate the following reaction?

A)lipoate
B)coenzyme A
C)FAD
D)NAD⁺
E)all of the above

Question 42

Give the products for the following reaction.

Question 43

How does CoASH used in biological systems to activate carboxylic acids?

A)converts carboxylic acids into amides
B)converts carboxyic acids into anhydrides
C)converts carboxylic acids into acid halides
D)converts carboxylic acids into thioesters
E)converts carboxylic acids into esters

Question 44

Which of the following reactions of amino acids is not catalyzed by PLP-requiring enzymes?

A)decarboxylation
B)transamination
C)α,β-elimination
D)α-keto esterification
E)C_α-C_β bond cleavage

Question 45

What does the term "Pyridoxal" stand for?

A)Pyridine aldehyde
B)Pyrrol oxyaldehyde
C)Pyrrolidine oxyaldehyde
D)Peroxy aldehyde
E)Pyrimidoxy aldehyde

Question 46

Give the purpose of TPP as a coenzyme.

A)a coenzyme that catalyzes the transfer of a one-carbon fragment
B)a coenzyme that catalyzes the carboxylation of the alpha carbon
C)a coenzyme that catalyzes the transfer of a three-carbon fragment
D)a coenzyme that catalyzes the carboxylation of the beta carbon
E)a coenzyme that catalyzes the transfer of a two-carbon fragment

Question 47

What is the first reaction in the catabolism of most amino acids?

A)transamination
B)decarboxylation
C)phosphorylation
D)aldolation
E)ligation

Question 48

Which of the following is the sequence of steps followed by biotin-dependent enzymes,as listed below? I.Transfer of the carboxyl group from carboxybiotin to the substrate
II)Activation of bicarbonate by ATP
III)Formation of carboxybiotin

A)I,II,III
B)I,III,II
C)II,I,III
D)II,III,I
E)III,II,I

Question 49

Propose a mechanism for the following reaction.

Question 50

Show the transimination (trans-Schiffization)reaction that happens in all PLP-requiring enzymes in which the amino acid substrate forms a Schiff base with PLP,thereby freeing the lysine side chain.

Question 51

Give the purpose of biotin.

Question 52

Which of the following reactions does the coenzyme biotin catalyze?

A)decarboxylation of an α-keto acid
B)decarboxylation of an α-carboxy acid
C)carboxylation of an α-carboxy acid
D)decarboxylation of a carbon adjacent to an ester or keto group
E)carboxylation of a carbon adjacent to an ester or keto group

Question 53

Which of the following are required species for biotin-dependent enzymes?

A)ATP
B)Mg⁺²
C)HCO₃^-
D)A and B
E)A,B,and C

Question 54

Which of the following coenzymes is required for the enzyme catalyzed reaction shown below? Xylose-5-P + Ribose-5-P Glyceraldehyde-3-P + Sedoheptulose-7-P

A)TPP
B)PLC
C)THF
D)NADH
E)NADPH

Question 55

Identify the compound below.

A)pyridoxine
B)ascorbic acid
C)thiamine
D)lipoate
E)niacin

Question 56

Give the product for the following reaction.

A)
B)
C)
D)
E)

Question 57

What metal ion is also required by biotin-dependent enzymes?

Question 58

Which of the following reactions is called an α,β-elimination of an amino acid?

A)I
B)II
C)III
D)IV
E)V

Question 59

Which of the following statements best describes what an "electron sink" is?

A)a free radical initiator for enzyme catalysis
B)a site for electron localization
C)a site for electron delocalization
D)a site that donates electrons for enzyme catalysis
E)a site that accepts electrons for enzyme catalysis

Question 60

Give the product for the following reaction.

A)
B)
C)
D)
E)

Question 61

Give the purpose of coenzyme B₁₂ in rearrangement reactions.

Question 62

Which of the following statements is true about 5-fluorouracil?

A)It is an anticancer drug.
B)It inhibits the enzyme thymidylate synthase.
C)It is an example of a mechanism-based inhibitor.
D)It is an example of a suicide inhibitor.
E)all of the above

Question 63

Give the products for the following reaction.

Question 64

Identify the first step in the mechanism for the vitamin KH₂-dependent carboxylation of glutamate.

A)The vitamin K base removes a proton from the gamma-carbon of the gluatamate.
B)The vitamin loses a proton from a phenolic OH group.
C)The dioxetane collapses to form a vitamin K base.
D)The base attacks molecular oxygen.
E)The glutamate carbanion attacks carbon dioxide.

Question 65

Which of the following statements is true about the vitamin KH₂?

A)It is the active coenzyme form of vitamin K.
B)Vitamin K is a quinone while vitamin KH₂ is a hydroquinone.
C)Vitamin KH₂ is the coenzyme for the enzyme that catalyzes the carboxylation of glutamate side chains in proteins to form Å-carboxyglutamates.
D)A and C
E)A,B,and C

Question 66

Propose a mechanism for the vitamin KH₂-catalyzed carboxylation of glutamate shown below.

Question 67

Propose a mechanism for the following coenzyme B₁₂-dependent enzyme-catalyzed reaction.

Question 68

Which of the following best represents the chemical reaction catalyzed by B₁₂-dependent enzymes?

A)
B)
C)
D)
E)

Question 69

Give the product for the following reaction.

A)
B)
C)
D)
E)

Question 70

Give the product for the following reaction.

A)
B)
C)
D)
E)

Question 71

Identify all group(s)that tetrahydrofolate transfers.

A)methylene
B)methyl
C)ethyl
D)formyl
E)A,B,and D

Question 72

Give the purpose of vitamin KH₂ as a coenzyme.

A)catalyzes the carboxylation of the alpha-carbon of the glutamate side chain in proteins
B)catalyzes the carboxylation of the beta-carbon of the glutamate side chain in proteins
C)catalyzes the carboxylation of the beta-carbon of the aspartate side chain in proteins
D)catalyzes the carboxylation of the gamma-carbon of the glutamate side chain in proteins
E)catalyzes the carboxylation of the alpha-carbon of the aspartate side chain in proteins

Question 73

Give the purpose of thymidylate synthase.

A)converts cytosine to guanine
B)converts guanine to cytosine
C)converts thymine to uracil
D)converts uracil to thymine
E)converts adenine to guanine

Question 74

Which of the following statements is not true about vitamin K?

A)The letter K comes from koagulation.
B)Vitamin K is required for proper Ca⁺² binding in blood clotting.
C)Kitase is the active coenzyme of vitamin K.
D)Vitamin K is synthesized by intestinal bacteria.
E)Vitamin K is formed in leaves of green plants.

Question 75

The thymine molecule used for the biosynthesis of DNA is synthesized from uracil as shown below. The structure of dTMP is a methylated dUMP.What is the structure of dTMP?

A)I
B)II
C)III
D)IV
E)V

Question 76

A quinone is part of the structure of vitamin

A)B₁₂.
B)B₁.
C)B₂.
D)C)
E)K)

Question 77

Through what enzymatic pathway is thymine biosynthesized?

Question 78

Which of the following statements is not true about the structure of vitamin B₁₂?

A)The structure was determined by Dorothy Hodgkin in 1955 using X-ray crystallography.
B)The structure has an adenosyl group.
C)The structure has a cyano group,HO^-,or H₂O.
D)The cyano group is coordinated to cobalt.
E)The structure cannot be synthesized by plants and animals.

Question 79

Which of the following statements is not true about the coenzyme tetrahydrofolate (THF)?

A)There are six different THF-coenzymes.
B)The coenzyme is used by enzyme-catalyzing reactions that donate a group containing a single carbon to their substrate.
C)THF results from the reduction of two double bonds of the precursor vitamin (folate).
D)Mammals synthesize the vitamin (folate)but bacteria cannot.
E)Homocysteine methyl transferase and glycinamide ribonucleotide are examples of enzymes that require THF-coenzyme.

Question 80

5-Fluorouracil is an anticancer drug that inhibits what essential enzyme?