MCQ Nucleotides & NA

Question 1

The compound that consists of ribose linked by an N-glycosidic bond to N-9 of adenine is:
A) a deoxyribonucleoside.
B) a purine nucleotide.
C) a pyrimidine nucleotide.
D) adenosine monophosphate.
E) adenosine.

Answer 1

E) adenosine.

Question 2

A major component of RNA but not of DNA is:

A) adenine. B) cytosine. C) guanine. D) thymine. E) uracil.

Answer 2

E) uracil.

Question 3

The difference between a ribonucleotide and a deoxyribonucleotide is:
A) a deoxyribonucleotide has an —H instead of an —OH at C-2.
B) a deoxyribonucleotide has α configuration; ribonucleotide has the β configuration at C-1.
C) a ribonucleotide has an extra —OH at C-4.
D) a ribonucleotide has more structural flexibility than deoxyribonucleotide.
E) a ribonucleotide is a pyranose, deoxyribonucleotide is a furanose.

Answer 3

a deoxyribonucleotide has an —H instead of an —OH at C-2.

Question 4

Which one of the following is true of the pentoses found in nucleic acids?
A) C-5andC-1ofthepentosearejoinedtophosphategroups.
B) C-5 of the pentose is joined to a nitrogenous base, and C-1 to a phosphate group.
C) The bond that joins nitrogenous bases to pentoses is an O-glycosidic bond.
D) Thepentosesarealwaysintheβ-furanoseforms.
E) The straight-chain and ring forms undergo constant interconversion.

Answer 4

D) Thepentosesarealwaysintheβ-furanoseforms.

Question 5

The phosphodiester bonds that link adjacent nucleotides in both RNA and DNA:
A) always link A with T and G with C.
B) are susceptible to alkaline hydrolysis.
C) are uncharged at neutral pH.
D) form between the planar rings of adjacent bases.
E) join the 3’ hydroxyl of one nucleotide to the 5’ hydroxyl of the next.

Answer 5

join the 3’ hydroxyl of one nucleotide to the 5’ hydroxyl of the next.

Question 6

The phosphodiester bond that joins adjacent nucleotides in DNA:
A) associates ionically with metal ions, polyamines, and proteins.
B) is positively charged.
C) is susceptible to alkaline hydrolysis.
D) Links C-2 of one base to C-3 of the next.
E) links C-3 of deoxyribose to N-1 of thymine or cytosine.

Answer 6

A) associates ionically with metal ions, polyamines, and proteins.

Question 7

The alkaline hydrolysis of RNA does not produce:
A) 2'- AMP.
B) 2',3'-cGMP.
C) 2'-CMP.
D) 3',5'-cAMP.
E) 3'-UMP.

Answer 7

D) 3’,5’-cAMP.

Question 8

In a double-stranded nucleic acid, cytosine typically base-pairs with:
A) adenosine. B) guanine. C) inosine. D) thymine. E) uracil.

Answer 8

B) guanine.

Question 9

Chargaff's rules state that in typical DNA:
A) A=G.
B) A=C.
C) A=U.
D) A+T=G+C. E) A+G=T+C.

Answer 9

E) A+G=T+C.

Question 10

In the Watson-Crick structure of DNA, the:
A) absence of 2’-hydroxyl groups allows bases to lie perpendicular to the helical axis.
B) adenine content of one strand must equal the thymine content of the same strand.
C) nucleotides are arranged in the A-form.
D) purine content (fraction of bases that are purines) must be the same in both strands.
E) two strands are parallel.

Answer 10

absence of 2’-hydroxyl groups allows bases to lie perpendicular to the helical axis.

Question 11

Which of the following is not true of all naturally occurring DNA?
A) Deoxyribose units are connected by 3’,5’-phosphodiester bonds.
B) The amount of A always equals the amount of T.
C) The ratio A+T/G+C is constant for all natural DNAs.
D) The two complementary strands are antiparallel.
E) Two hydrogen bonds form between A and T.

Answer 11

C) The ratio A+T/G+C is constant for all natural DNAs

Question 12

In the Watson-Crick model of DNA structure (now called B-form DNA):
A) a purine in one strand always hydrogen bonds with a purine in the other strand.
B) A–T pairs share three hydrogen bonds.
C) G–C pairs share two hydrogen bonds.
D) the 5’ ends of both strands are at one end of the helix.
E) the bases occupy the interior of the helix.

Answer 12

E) the bases occupy the interior of the helix.

Question 13

In nucleotides and nucleic acids, syn and anti conformations relate to:
A) base stereoisomers.
B) rotation around the phosphodiester bond.
C) rotation around the sugar-base bond.
D) sugar pucker.
E) sugar stereoisomers.

Answer 13

C) rotation around the sugar-base bond.

Question 14

In double-stranded DNA:
A) only a right-handed helix is possible.
B) sequences rich in A–T base pairs are denatured less readily than those rich in G–C pairs.
C) the sequence of bases has no effect on the overall structure.
D) the two strands are parallel.
E) the two strands have complementary sequences.

Answer 14

E) the two strands have complementary sequences.

Question 15

Triple-helical DNA structures can result from Hoogsteen (non Watson-Crick) interactions. These interactions are primarily:
A) covalent bonds involving deoxyribose.
B) covalent bonds involving the bases.
C) hydrogen bonds involving deoxyribose.
D) hydrogen bonds involving the bases.
E) hydrophobic interactions involving the bases.

Answer 15

D) hydrogen bonds involving the bases.

Question 16

Double-stranded regions of RNA:
A) are less stable than double-stranded regions of DNA.
B) can be observed in the laboratory, but probably have no biological relevance.
C) can form between two self-complementary regions of the same single strand of RNA.
D) do not occur.
E) have the two strands arranged in parallel (unlike those of DNA, which are antiparallel).

Answer 16

C) can form between two self-complementary regions of the same single strand of RNA.

Question 17

Compounds that generate nitrous acid (such as nitrites, nitrates, and nitrosamines) change DNA molecules by:
A) breakage of phosphodiester bonds.
B) deamination of bases.
C) depurination.
D) formation of thymine dimers.
E) transformation of A → T.

Answer 17

B) deamination of bases.

Question 18

In the chemical synthesis of DNA:
A) the dimethoxytrityl (DMT) group catalyzes formation of the phosphodiester bond.
B) the direction of synthesis is 5’ to 3’.
C) the maximum length of oligonucleotide that can be synthesized is 8-10 nucleotides.
D) the nucleotide initially attached to the silica gel support will become the 3’ end of the finished
product.
E) the protecting cyanoethyl groups are removed after each step.

Answer 18

D) the nucleotide initially attached to the silica gel support will become the 3’ end of the finished
product.

Question 19

In living cells, nucleotides and their derivatives can serve as:
A) carriers of metabolic energy.
B) enzyme cofactors.
C) intracellular signals.
D) precursors for nucleic acid synthesis.
E) all of the above.

Answer 19

E) all of the above.