Deck 18: Nucleotide Metabolism

Question 1

Which is the source of the ribose ring in purine nucleotides?

A)ATP.
B)AMP.
C)PRPP.
D)cGDP.

Answer 1

PRPP.

Question 2

The purine ring system is shown below.What is the source of the C-6 atom during de novo biosynthesis of purines?

A)Carbon dioxide.
B)Tetrahydrofolate.
C)Carbamoyl phosphate.
D)Glycine.

Answer 2

Carbon dioxide.

Question 3

Which amino acid is not directly involved in the de novo biosynthesis of purines?

A)Glycine.
B)Glutamine.
C)Aspartate.
D)Arginine.

Answer 3

Arginine.

Question 4

The purine ring system is shown below.What is the source of the atoms 5 and 7 during de novo biosynthesis of purines?

A)Glycine.
B)Glutamine.
C)Aspartate.
D)Arginine.

Question 5

The pyrimidine ring system is shown below.What is the source of the N-1 during the de novo biosynthesis of pyrimidines?

A)Aspartate.
B)Urea.
C)Asparagine.
D)IMP.

Question 6

The purine ring system is shown below.What is the source of the carbon atoms 2 and 8 during de novo biosynthesis of purines?

A)Carbon dioxide.
B)Aspartate.
C)10-formyltetrahydrofolate.
D)Glutamine.

Question 7

Which enzyme catalyzes the step in purine nucleotide biosynthesis that is the principal site of regulation for the pathway?

A)Adenylsuccinate lyase.
B)OPM decarboxylase.
C)IMP cyclohydrolase.
D)Glutamine-PRPP amidotransferase.

Question 8

The pyrimidine ring system is shown below.What is the source of the N-3 during the de novo biosynthesis of pyrimidines?

A)Ammonia.
B)Glutamine.
C)Arginine.
D)Urea.

Question 9

The pyrimidine ring system is shown below.What is the source of the C-2 during the de novo biosynthesis of pyrimidines?

A)Aspartate.
B)PRPP.
C)Bicarbonate.
D)Tetrahydrofolate.

Question 10

A ribose sugar is added to ________ rings after their synthesis and to ________ rings during their synthesis.

A)purine;pyrimidine
B)pyrimidine;purine
C)purine;purine
D)pyrimidine;pyrimidine

Question 11

________ is a precursor for the de novo synthesis of AMP and GMP.

A)OMP
B)XMP
C)Adenylosuccinate
D)IMP

Question 12

The first step in the de novo biosynthesis of IMP is a reaction between glutamine and PRPP.Which statement is not true about this reaction?

A)An amine group is attached to the anomeric carbon atom of the ribose ring.
B)The configuration of the anomeric carbon atom is inverted from β to α.
C)A pyrophosphate is lost from PRPP.
D)The reaction is catalyzed by glutamine-PRPP aminotransferase.

Question 13

Which are purines?

A)Adenine and thymine.
B)Guanine and adenine.
C)Cytosine and thymine.
D)Uracil and guanine.

Question 14

The purine ring system is shown below.What is the source of the nitrogen atoms 3 and 9 during the de novo biosynthesis of purines?

A)Aspartate.
B)Glycine.
C)Arginine.
D)Glutamine.

Question 15

Which structure below is PRPP?

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

Question 16

Four of the ten enzymes required for the biosynthesis of IMP are listed below.In which order do the reactions these enzymes catalyze occur during the synthesis of IMP?
1.IMP cyclohydrolase
2.GAR synthase
3.glutamine-PRPP amidotransferase
4.AIR carboxylase

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

Question 17

Which is a method by which the synthesis of AMP or GMP is regulated?

A)Covalent modification.
B)Feedback inhibition.
C)Feed-forward activation.
D)Competitive inhibition.

Question 18

The purine ring system is shown below.What is the source of the N-1 atom during de novo biosynthesis of purines?

A)Glycine.
B)Glutamine.
C)Aspartate.
D)Arginine.

Question 19

The first nucleotide product in the de novo biosynthetic pathway of purines is

A)AMP.
B)GMP.
C)IMP.
D)XMP.

Question 20

Which is a common precursor in the de novo synthesis of purine nucleotides?

A)Inosine 5'-monophosphate.
B)Xanthosine monophosphate.
C)Orotate.
D)Adenylosuccinate.

Question 21

Substrates for reduction to form deoxyribonucleotides are

A)mononucleotides.
B)trinucleotides.
C)dinucleotides.
D)B and C.
E)All of the above.

Question 22

Which type of enzymes catalyze the phosphorylation of dADP,dGDP and dCDP?

A)Nucleotide phosphorylases.
B)Nucleoside diphosphate kinases.
C)Triphosphatases.
D)Deoxyribosylphosphatases.

Question 23

Which is the correct order for the synthesis of CTP?

A)UMP → UDP→ UTP → CTP
B)GMP → GDP→ GTP → CTP
C)UTP → TTP→ CTP
D)UMP → CMP→ CDP → CTP

Question 24

The source of the hydrogen to form water during the reduction of nucleoside triphosphates is ________.

A)thioredoxin
B)NADP
C)NADH
D)NADPH
E) FADH₂

Question 25

Which is used to synthesize CTP?

A)CMP.
B)GMP.
C)TMP.
D)UMP.

Question 26

What is unusual about the reaction catalyzed by ribonucleotide reductase?

A)It involves the conversion of -SH groups to -OH groups.
B)It uses a rare derivative of tetrahydrofolate.
C)It has a free radical mechanism.
D)This enzyme and its reaction occur only in a few species of archaebacteria.

Question 27

The pyrimidine ring system is shown below.What is the source of the carbons 4,5 and 6 during the de novo biosynthesis of pyrimidines?

A)Glutamine.
B)Aspartate.
C)3 bicarbonate ions.
D)Pyruvate.

Question 28

Carbamoyl phosphate synthetase I is located in the ________ in eukaryotes and uses ________ as a nitrogen source.

A)mitochondria;glutamine
B)mitochondria;ammonia
C)cytosol;glutamine
D)cytosol;ammonia

Question 29

Which catalytic site is not contained in the eukaryotic multifunctional protein dihydroorotate synthase?

A)Orotate phosphoribosyltransferase.
B)ATCase.
C)Carbamoyl phosphate synthetase II.
D)Dihydroorotase.

Question 30

The reduction of ribonucleotides by ribonucleotide reductase requires the formation of a(n)________.

A)covalent intermediate
B)free radical protein
C)intermediate methyl group
D)acid-base catalyst

Question 31

Which is the correct order for the enzymes needed to convert UMP to CTP?

A)Nucleoside diphosphate kinase;uridylate kinase;CTP synthetase.
B)Uridylate kinase;nucleoside diphosphate kinase;CTP synthetase.
C)Uridylate kinase;CTP synthetase;nucleoside diphosphate kinase.
D)CTP synthetase;nucleoside diphosphate kinase;uridylate kinase.

Question 32

Increased concentrations of ATP and GTP increase the rates of ________ nucleotide synthesis to help balance supplies of nucleotides in cells.

A)pyrimidine
B)both purine and pyrimidine
C)cytosine
D)purine

Question 33

The conversion of UTP to CTP involves ________.

A)hydrolysis of a phosphate group
B)oxidation of an OH group
C)transfer of an NH₂ group
D)formation of a carbon-carbon double bond

Question 34

High levels of ________ will almost totally inhibit ATCase.

A)CTP
B)ATP
C)CTP and UTP
D)ADP and UDP

Question 35

Which is the precursor of all pyrimidine ribo- and deoxyribonucleotides?

A)dTMP.
B)CTP.
C)IMP.
D)UMP.

Question 36

Eukaryotic cells maintain the correct balance of deoxyribonucleotides needed in a species DNA by ________.

A)controlling the activity of ribonucleotide reductase
B)controlling the specificity of ribonucleotide reductase
C)controlling both the specificity and activity of ribonucleotide reductase at the same time
D)feedback inhibition
E)controlling the balance of NADPH formed

Question 37

Which occurs when CTP synthase converts UTP to CTP?

A)Glutamine → Glutamate
B)Glutamate → Glutamine
C)Aspartate → Glutamate
D)Glutamine → Glycerate

Question 38

Which is not a direct precursor of pyrimidines in their de novo biosynthesis?

A)HCO₃-.
B)Glutamine.
C)Glycine.
D)Aspartate.

Question 39

Inhibition of ATCase by a ________ nucleotide and activation of ATCase by a ________ nucleotide keep the balance of purine and pyrimidine pools in E.coli.

A)purine (ATP);purine (ATP)
B)pyrimidine;pyrimidine
C)pyrimidine;purine (ATP)
D)purine (ATP);pyrimidine

Question 40

The ribonucleotides that are reduced to deoxyribonucleotides in most organisms are ________.

A)nucleosides
B)mononucleotides
C)dinucleotides
D)trinucleotides

Question 41

The excretory products of uric acid catabolism vary among organisms depending on their ability to ________.

A)tolerate the end-product
B)remove the end-product to less toxic products
C)solubilize the end-product
D)remove an end-product like ammonia to the environment
E)All of the above

Question 42

DNA synthesis is often measured by using radioactive

A)biotin.
B)thymine.
C)thiamine.
D)thymidine.
E)All of the above.

Question 43

In birds and reptiles,purine nucleotides and surplus nitrogen from amino acid catabolism is disposed of in the form of ________ while humans form that,as well as ________ in nitrogenous waste.

A)xanthine,uric acid
B)uric acid;xanthine
C)uric acid;urea
D)urea;uric acid
E)urea;guanine

Question 44

Virtually all organisms and tissues can synthesize nucleotides.

Question 45

5-methylcytidine is a common modified base in mammalian DNA that plays roles in ________.

A)restriction endonucleases
B)regulation of transcription
C)chromatin assembly
D)both B and C

Question 46

The major end product of purine degradation in humans is

A)allantoin.
B)guanine.
C)urate.
D)ammonia.

Question 47

Lesch-Nyhan syndrome,a result of hypoxanthine-guanine phosphoribosyltransferase deficiency,there is a(n)________.

A)accumulation of hypoxanthine
B)accumulation of GMP
C)complete breakdown of purine biosynthesis
D)excess of degradation of IMP and GMP
E)accumulation of IMP

Question 48

When phosphoribosyl pyrophosphate (PRPP)is used to form AMP from adenine (as well as in numerous other cell reactions),the reaction is rendered irreversible because

A)PRPP has such a high affinity for the enzyme involved.
B)the rate of the reaction favors formation of the product(s).
C)this reaction is thermodynamically feasible.
D)the presence of pyrophosphatase hydrolyzes pyrophosphate formed.
E)All of the above.

Question 49

Although dUTP can be synthesized from UDP and ATP,it is not accidentally incorporated into DNA in place of ________ because it is rapidly hydrolyzed

A)dATP
B)dGTP
C)dCTP
D)dTTP

Question 50

Pigs excrete guanine rather that further catabolizing it because ________.

A)deamination leads to a product toxic to pigs
B)guanase is produced in extremely small amounts and is only activated under conditions of starvation
C)guanine is a component of antibiotics fed to pigs to enhance their growth
D)pigs lack the enzyme guanase

Question 51

Pyrimidines are catabolized to ammonia,bicarbonate,and either ________ (from cytosine or uracil)or ________ (from thymine).

A)succinyl CoA;acetyl CoA
B)β-alanine;β-aminobutyrate
C)fumarate;succinyl CoA
D)acetyl CoA;succinyl CoA
E)acetyl CoA;acetyl CoA

Question 52

In the reactions catalyzed by xanthine oxidase,electrons are transferred to ________ to form ________.

A)O₂;H₂O₂
B)H₂O₂;O₂
C)H₂O;O₂
D)O₂;H₂O

Question 53

Xanthine oxidase catalyzes the formation of ________.

A)xanthine
B)uric acid
C)hypoxanthine
D)xanthine and uric acid
E)All of the above

Question 54

Dihydrofolate reductase and thymidylate synthetase are major targets for anticancer drugs because

A)these enzymes are unique in cancer cells.
B)cancer cells lack sufficient amounts of these enzymes.
C)cancer cells grow rapidly and are very dependent upon the activities of these enzymes.
D)they donate one-carbon groups.
E)All of the above.

Question 55

During de novo biosynthesis of the purine nucleotides,the purine ring is first formed as a free base before being attached to the ribose 5-phosphate moiety.

Question 56

The action of the enzyme urease on urea produces ________.Urease is found in ________.

A)uracil;plants only
B)uracil;all eukaryotes
C)ammonia;all organisms
D)ammonia;plants,crustaceans and some marine invertebrates

Question 57

The one-carbon group needed to convert dUMP into dTMP is derived from

A)methanol.
B)5,10-methylenetetrahydrofolate.
C)glycine.
D)serine.
E)biotin.

Question 58

Which is the correct order for the synthesis of dTMP?

A)dUDP → dUTP→ dTTP → dTDP→ dTMP
B)UMP → UDP→ dUDP → dUMP→ dTMP
C)UMP → TMP→ dTMP
D)UMP → dUMP→ dTMP

Question 59

dUTP is not a direct precursor of dTTP because ________.

A)there are no enzymes for this reaction
B)dUTP controls DNA synthesis
C)it could possibly be incorporated into DNA
D)All of the above

Question 60

Allopurinol may be used to treat gout due to an excess of uric acid production because it can be converted to oxypurinol by ________,and oxypurinol strongly inhibits ________.

A)xanthine dehydrogenase;xanthine dehydrogenase
B)xanthine dehydrogenase;sodium urate
C)urease;xanthine dehydrogenase
D)xanthine dehydrogenase;urease
E)urease;urease

Question 61

About 3% of all deoxycytidylate residues in mammalian DNA are methylated after DNA is synthesized.

Question 62

Enzymes that synthesize UMP are located on both sides of the mitochondrion in eukaryotic cells.

Question 63

In pyrimidine nucleotide biosynthesis orotate is the molecule that displaces the pyrophosphate group on PRPP.

Question 64

Allantoin is the major end product of purine degradation in most mammals.

Question 65

When a purine or a purine triphosphate is bound to the specificity site of ribonucleotide reductase,the activity of the catalytic site of the enzyme is specific for a pyrimidine or a pyrimidine triphosphate.

Question 66

PRPP synthetase is inhibited by several purine ribonucleotides but only at concentrations lower than those usually found in the cell so there remains a supply for other cell reactions.

Question 67

In eukaryotes all enzymes for the biosynthesis of the pyrimidine nucleotides occur exclusively in the cytosol.

Question 68

No distinctive excretory products are formed from the catabolism of pyrimidines.

Question 69

The cofactor,methylenetetrahydrofolate,can donate a variety of one-carbon groups as well as act as a reducing agent in biochemical reactions.

Question 70

In the de novo synthesis of the deoxyribonucleotides,the deoxy form of PRPP is used in place of the PRPP used in the synthesis of the ribonucleotides.

Question 71

Ribonucleotides are produced from oxidation of the deoxyribonucleotides at the 2' carbon atom.

Question 72

The pathway for the synthesis of IMP releases considerable energy and is an important source of ATP.

Question 73

Purines and pyrimidines formed during digestion of food are more likely to be salvaged than those formed inside the cell.

Question 74

Channeling is an important process in the biosynthesis of pyrimidine nucleotides in mammals.

Question 75

The coenzyme biotin is required for the carboxylation of aminoimidazole ribonucleotide (AIR)during the de novo synthesis of IMP by the enzyme AIR carboxylase.

Question 76

In prokaryotes,carbamoyl phosphate is an intermediate in the de novo biosynthesis of pyrimidine nucleotides.

Question 77

The structure of carbamoyl phosphate synthetase of E.coli contains a tunnel that protects unstable intermediates from degradation by water.

Question 78

dCMP,dGMP,dAMP and dTMP are substrates for a reductase that phosphorylates them to the triphosphate levels for incorporation into DNA.

Question 79

Modified nucleotides are rare and have not been shown to play significant roles in cell processes.

Question 80

Nucleotides have a β configuration about the anomeric carbon atom of the ribose or deoxyribose ring.