Nucleotide Metabolism

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 alpha configuration; ribonucleotide has the beta 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) 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-5 and C-1 of the pentose are joined to phosphate groups.
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) The pentoses are always in the β-furanose forms.
E) The straight-chain and ring forms undergo constant interconversion.

Answer 4

D) The pentoses are always in the β-furanose forms.

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

E) 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

The DNA oligonucleotide abbreviated pATCGAC:

A) has 7 phosphate groups. 
B) has a hydroxyl at its 3'end.
C) has a phosphate on its 3' end. 
D) has an A at its 3' end. 
E) violates Chargaff's rules.

Answer 8

B) has a hydroxyl at its 3’end.

Question 9

For the oligoribonucleotide pACGUAC:

A) the nucleotide at the 3’ end has a phosphate at its 3’ hydroxyl.
B) the nucleotide at the 3’ end is a purine.
C) the nucleotide at the 5’ end has a 5’ hydroxyl.
D) the nucleotide at the 5’ end has a phosphate on its 5’ hydroxyl.
E) the nucleotide at the 5’ end is a pyrimidine.

Answer 9

D) the nucleotide at the 5’ end has a phosphate on its 5’ hydroxyl.

Question 10

The nucleic acid bases:

A) absorb ultraviolet light maximally at 280 nm.
B) are all about the same size.
C) are relatively hydrophilic.
D) are roughly planar.
E) can all stably base-pair with one another.

Answer 10

D) are roughly planar.

Question 11

Which of the following statements concerning the tautomeric forms of bases such as uracil is correct?

A) The all-lactim form contains a ketone group.
B) The lactam form contains an alcohol group.
C) The lactam form predominates at neutral pH.
D) They are geometric isomers.
E) They are stereoisomers.

Answer 11

C) The lactam form predominates at neutral pH.

Question 12

In a double-stranded nucleic acid, cytosine typically base-pairs with:

A) adenosine. 
B) guanine. 
C) inosine. 
D) thymine. 
E) uracil.

Answer 12

B) guanine

Question 13

In the Watson-Crick model for the DNA double helix (B form) the A-T and G-C base pairs share which one of the following properties?

A) The distance between the two glycosidic (base-sugar) bonds is the same in both base pairs, within a few tenths of an angstrom.
B) The molecular weights of the two base pairs are identical.
C) The number of hydrogen bonds formed between the two bases of the base pair is the same.
D) The plane of neither base pair is perpendicular to the axis of the helix.
E) The proton-binding groups in both base pairs are in their charged or ionized form.

Answer 13

A) The distance between the two glycosidic (base-sugar) bonds is the same in both base pairs, within a few tenths of an angstrom

Question 14

The experiment of Avery, MacLeod, and McCarty in which nonvirulent bacteria were made virulent by transformation was significant because it showed that:

A) bacteria can undergo transformation.
B) genes are composed of DNA only.
C) mice are more susceptible to pneumonia than are humans.
D) pneumonia can be cured by transformation.
E) virulence is determine genetically.

Answer 14

B) genes are composed of DNA only.

Question 15

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 15

E) A + G = T + C.

Question 16

Based on Chargaff’s rules, which of the following are possible base compositions for double-stranded DNA?

%A %G %C %T %U
A) 5 45 45 5 0 
B) 20 20 20 20 20
C) 35 15 35 15 0 
D) all of the above 
E) none of the above

Answer 16

A) 5 45 45 5 0

Question 17

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 17

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