Chapter 8 Nucleotides and Nucleic Acids (Ed. 6 test bank)

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

Adenosine

Question 2

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 beta-furanose forms.
E) The straight-chain and ring forms undergo constant interconversion.

Answer 2

The pentoses are always in the beta-furanose forms

Question 3

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 3

Are roughly planar

Question 4

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 4

The lactam form predominates at neutral pH

Question 5

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 5

A + G = T + C

Question 6

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 6

Nonspecific base-stacking interaction between two adjacent bases in the same strand

Question 7

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 7

Rotation around the sugar-base bond

Question 8

B-form DNA in vivo is a ________-handed helix, _____ Å in diameter, with a rise of ____ Å per base pair.

A) left; 20; 3.9
B) right; 18; 3.4
C) right; 18; 3.6
D) right; 20; 3.4
E) right; 23; 2.6

Answer 8

Right-handed;
20 Å in diameter;
3.4 Å rise per base pair

Question 9

In DNA sequencing by the Sanger (dideoxy) method:

A) radioactive dideoxy ATP is included in each of four reaction mixtures before enzymatic synthesis of complementary strands.
B) specific enzymes are used to cut the newly synthesized DNA into small pieces, which are then separated by electrophoresis.
C) the dideoxynucleotides must be present at high levels to obtain long stretches of DNA sequence.
D) the role of the dideoxy CTP is to occasionally terminate enzymatic synthesis of DNA where Gs
occur in the template strands.
E) the template DNA strand is radioactive.

Answer 9

The role of the dideoxy CTP is to occasionally terminate enzymatic synthesis of DNA where Gs occur in the template strand

Question 10

How are a nucleoside and a nucleotide similar and how are they different?

Answer 10

Both have a nitrogenous base and a pentose;

Nucleotides also have a phosphate group, which nucleosides lack

Question 11

Compounds that contain a nitrogenous base, a sugar, and a phosphate group are called (a)_________________. Two purines found in DNA are (b)______________ and __________________. A pyrimidine found in all DNA but in only some RNA is (c)_________________. In DNA, the base pair (d)___-___ is held together by three hydrogen bonds; the base pair (e)___-___ has only two such bonds.

Answer 11

a) nucleotides
b) adenine and guanine
c) thymidine
d) G-C
e) A-T

Question 12

The composition (mole fraction) of one of the strands of a double-helical DNA is [A] = 0.3, and [G] = 0.24. Calculate the following, if possible. If impossible, write “I.”

For the same strand: 
[T] = (a) \_\_\_\_ 
[C] = (b) \_\_\_\_
[T]+[C] = (c) \_\_\_\_ 
For the other strand:
[A] = (d) \_\_\_\_
[T] = (e) \_\_\_\_
[A] + [T] = (f) \_\_\_\_ 
[G] = (g) \_\_\_\_
[C] = (h) \_\_\_\_
[G] + [C] = (i) \_\_\_\_

Answer 12

a) I
b) I
c) 0.46
d) I
e) 0.3
f) I
g) I
h) 0.24
i) I

Question 13

What is the approximate length of a DNA molecule (in the B form) containing 10,000 base pairs?

Answer 13

3.4 Å x 10,000 = 34,000 Å = 3.4 μm

Question 14

In one sentence, identify the most obvious structural difference between A-form (Watson-Crick) DNA and Z-form DNA.

Answer 14

A-form DNA is a right-handed helix; Z-form DNA is a left-handed helix

Question 15

Describe qualitatively how the tm for a double-stranded DNA depends upon its nucleotide composition.

Answer 15

In general, the higher the proportion of G and C, the higher the melting temperature, tm. More thermal energy is required to break the three hydrogen bonds holding GC pairs than to break the two hydrogen bonds holding A=T pairs.

Question 16

A solution of DNA is heated slowly until the tm is reached. What is the likely structure of the DNA molecules at this temperature?

Answer 16

The DNA molecules are partially denatured; in each molecule approximately 50% of the DNA is single-stranded and 50% is double-helical. The single-stranded regions, which appear as “bubbles” within the molecules, are those which denatured at lower temperatures because of their higher content of A–T base pairs.

Question 17

Mouse DNA hybridizes more extensively with human DNA than with yeast DNA. Explain by describing the factor or factors that determine extent of hybridization.

Answer 17

In general, the more similar the sequences in two DNA molecules are, the more readily they will hybridize. Because the evolutionary distance between mouse and yeast is greater than that between mouse and human, mouse and human DNA sequences are more similar than those of mouse and yeast.