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Chapter 4 DNA, RNA, and the Flow of Genetic Information
Matching Questions
Use the following to answer questions 1-10:
Choose the best answer from the list below. Not all of the answers will be used.
a) annealing
b) mRNA molecules
c) synonyms
d) introns
e) amino acids
f) Tm
g) viruses
h) exons
i) Erwin Chargaff
j) release factors
k) gene expression
l) Rosalyn Franklin
m) proteins
n) translation
o) Francis Crick
p) TDNA
q) bacteria
1. ____________ The information-carrying intermediates produced during transcription.
Ans: b
Section: Introduction
2. The flow of genetic information from DNA to protein is called ____________.
Ans: k
Section: Introduction
3. ____________ Scientist who noted the A:T and G:C ratios in DNA are approximately 1:1.
Ans: i
Section: 4.2
4. The temperature at which half of the DNA helical character is lost is referred to as
____________.
Ans: f
Section: 4.3
5. DNA renaturation after melting is called ____________.
Ans: a
Section: 4.3
Page 1
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6. Noncoding regions within a gene are known as ______________.
Ans: d
Section: 4.7
7. ____________ Organisms in which the flow of genetic information can be RNADNA.
Ans: g
Section: 4.4
8. Codons that specify the same amino acids are termed ____________.
Ans: c
Section: 4.6
9. Three-base codons encode for specific ____________.
Ans: e
Section: Introduction
10. Stop codons are read by ____________.
Ans: j
Section: 4.6
Fill-in-the-Blank Questions
11. The enzyme that is capable of synthesizing DNA from an RNA template is
__________________.
Ans: reverse transcriptase Section: 4.4
12. __________________ is the most abundant type of RNA in a cell.
Ans: Ribosomal RNA or rRNA Section: 4.4 and Table 4.3
13. Each amino acid residue in a protein is encoded by a set of three bases in an mRNA referred to
collectively as a(n) __________________.
Ans: codon Section: Introduction
14. In an amino acyl-tRNA, the amino acid is attached to the CCA sequence at the _________ end
of the tRNA.
Ans: 3'
Section: 4.5 and Figure 4.34
15. mRNAs of higher organisms are formed by splicing together _________________ after removal
of intervening sequences.
Ans: exons Section: 4.7
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16. In bacterial mRNA, the initiating AUG codon is preceded several nucleotides away by a purinerich sequence called the __________________ , which base-pairs with a complimentary
sequence in an rRNA.
Ans: Shine-Dalgarno sequence Section: 4.6
17. The nucleoside that is composed of a D-ribose linked to a cytosine base is called
__________________.
Ans: cytidine Section: 4.1
18. The phenomenon that stacked bases in double-helical DNA absorbed less UV light than the
unstacked bases in single-stranded DNA is referred to as _________________.
Ans: hypochromism or the hypochromic effect Section: 4.3
19.
________________molecules participate in the splicing of mRNA.
Ans: Small nuclear RNA or snRNA Section: 4.5
20.
In DNA and RNA synthesis, the new strand growth is always in the ___________ direction.
Ans: 5' to 3' Section: 4.4
Multiple-Choice Questions
21. The difference in RNA bases compared to DNA bases is
A)
RNA contains A instead of T.
D)
RNA contains A instead of U.
B)
RNA contains U instead of G.
E)
None of the above.
C)
RNA contains U instead of T.
Ans: C Section: 4.1
22. How does a nucleotide differ from a nucleoside?
A)
Nucleosides are found in DNA, whereas nucleotides are found in RNA.
B)
Purines are only found in nucleotides.
C)
Nucleosides contain only deoxyribose sugars.
D)
A nucleotide is a nucleoside with a phosphate ester linked to the sugar.
E)
None of the above.
Ans: D Section: 4.1
23. What is the nucleotide sequence on the DNA template strand that yields the CUA codon for
leucine?
A)
AUC
D)
GAT
B)
TAG
E)
CUA
C)
CTA
Ans: B Section: 4.5
24. Although the right-handed double helix is the most well- known DNA structure, DNA can also
form:
A) triple strands B) straight chains C) branched chains D) left-handed helices E) All of
the above
Ans: D Section: 4.2
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25. The technique(s) used by Franklin and Wilkins to deduce the structure of DNA was
A)
absorbance spectrophotometry.
D)
All of the above.
B)
electron microscopy.
E)
None of the above.
C)
x-ray diffraction.
Ans: C Section: 4.2
26. The feature(s) of DNA deduced by Watson and Crick included
A)
two antiparallel polynucleotide chains coiled in a helix around a common axis.
B)
the pyrimidine and purine bases lie on the inside of the helix.
C)
the bases are nearly perpendicular to the axis.
D)
All of the above.
E)
None of the above.
Ans: D Section: 4.2
27. The chemical forces that contribute to the stability of the DNA due to the base stacking present
in the DNA helix are
A)
hydrogen bonds.
D)
b and c.
B)
van der Waals.
E)
None of the above.
C)
disulfide bonds.
Ans: B Section: 4.2
28. What is the approximate error rate in DNA replication?
A) 1  108 B) 1  105 C) 1  1014 D) 1  1011
Ans: A Section: 4.4
E) None of the above.
29. What are the common promoter regions found in bacterial genes?
A)
a Hogness box at about –10 and a –35 region
B)
a TATA box at about –25 and a CAAT box at about –75
C)
a Pribnow box at about –10 and a TATA box at about –25
D)
a TATA box at about –25 and a –35 region
E)
None of the above.
Ans: E Section: 4.5
30. Which of the following is correct concerning the adaptor molecule tRNA?
A)
tRNA contains an anticodon sequence that serves as the template recognition site.
B)
The amino acid is attached to the 5' end of tRNA.
C)
tRNA contains a poly A tail at the 3' end.
D)
tRNA is the smallest RNA in the cell.
E)
tRNA serves as the gene in some viruses.
Ans: A Section: 4.5 and Table 4.3
31. Features of the genetic code include
A)
a codon is defined by three bases.
B)
the code overlaps.
C)
the code is degenerate.
Ans: D Section: 4.6
D)
E)
a and c.
a and b.
32. The first amino acid in bacterial proteins is
A) Met. B) fGly. C) fMet. D) Gly. E) None of the above.
Ans: C Section: 4.6
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33. The advantage(s) that most genes of higher eukaryotes, such as birds and mammals, are split
include
A)
the potential for generating related
D)
a and b.
proteins.
B)
the preservation of functional units (e.g. E)
None of the above.
catalytic site).
C)
the resistance to mutation.
Ans: D Section: 4.7
34. The sites for intron splicing consensus sequences are often
A)
AC-------------------AAAA.
D)
All of the above.
B)
GU-------------------AG.
E)
None of the above.
C)
AU-------------------GC.
Ans: B Section: 4.7
35. Ribosomes are composed of
A) DNA. B) rRNA. C) protein.
Ans: E Section: 4.5
D) a and b
E) b and c.
Short-Answer Questions
36. Draw two nucleotides in DNA showing the linkage between the sugars linked.
Base
Ans:
Base
H
H
O
O
O
O CH2
O
P O CH2
O
O
O
P O
O
The 3' oxygen of one nucleotide is linked to a phosphorous atom, which is linked to the
oxygen on the 5' carbon on the next sugar. Two extra oxygens should be attached to the
phosphorus atom, and the phosphate should be shown ionized at neutral pH. There should
be no oxygen at the 2' position of the sugar. (Note: the partial double-bond character
shown above is optional and would disperse the charge. With the charge as shown above
only the uncharged oxygen has a double bond.)
Section: 4.3 and Figure 4.25
37. What advantage do phosphodiesters have compared to other esters?
Ans: The negative charge serves to repel nucleophilic species such as OH-. Thus, the
phophodiester linkage is more stable because it is more resistant to hydrolytic cleavage.
Section: 4.1
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38. Describe the DNA helix proposed by Watson and Crick.
Ans: The DNA model proposed by Watson and Crick contains two DNA polymer strands
coiled around a common axis. The strands are orientated in opposite directions from 5' to
3' (antiparallel), and the two strands are twisted in a right-handed coil. The sugarphosphate backbone is located on the outside. The base pairs are stacked in the center of
the helix and are stabilized by specific hydrogen bonds between AT and GC base pairs.
The base pairs lie perpendicular to the axis, and there are 10 base pairs per turn with a
helical repeat of 34 angstroms.
Section: 4.2
39. Draw the hydrogen-bonded base pairs of A to T and show why A does not hydrogen-bond to C.
H
H
H
Ans:
N H
N
N
d-Rib
N
O
CH3
N
H N
N
N
O
N H H N
N
d-Rib
N
N
N
N
O
d-Rib
d-Rib
No H-bonds can form between the functional
groups in A and C.
Section: 4.2
40. Briefly describe the Meselson and Stahl experiment that indicated that DNA replication is
semiconservative.
Ans: Meselson and Stahl grew bacteria in the presence of 15N, or “heavy” nitrogen. They
rapidly replaced the 15N media with 14N, or light nitrogen. DNA was extracted at various
time intervals during the growth of the bacteria, representing different stages of
replication (generations). They examined the DNA using density-gradient equilibrium
sedimentation and observed that no “heavy” DNA was present in the first generation, but
that the DNA was intermediate between light and heavy. After the second generation,
there were equal amounts of intermediate and light. This confirmed that one strand of the
parent DNA is present in each daughter strand of replicated DNA.
Section: 4.3
41. What is DNA hybridization?
Ans: DNA hybridization is the process whereby strands of nearly complementary DNA from
different organisms or one strand of DNA and one strand of RNA base pair to form a
helix.
Section: 4.3
42. What are the minimal components required for DNA replication?
Ans: DNA replication requires DNA template; all four deoxynucleoside triphosphates (dATP,
dTTP, dGTP, dCTP (dNTPs)); a primer polynucleotide(DNA or RNA) with a free 3' OH;
magnesium ion; and DNA polymerase.
Section: 4.4
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43. Draw how the dNTP is added to a DNA strand at the 3' end.
Ans: The drawing should indicate clearly how the 3'OH oxygen attacks the α phosphate on the
incoming dNTP with the displacement of pyrophosphate.
Section: 4.4 and Figure 4.25
44. How does RNA polymerase differ from DNA polymerase?
Ans: Although similar in many respects to DNA polymerase, RNA polymerase does not
require a primer, nor does it have the nuclease “proofreading” capacity.
Section: 4.5
45. What is a consensus sequence?
Ans: A consensus sequence is a common sequence motif found in a number of genes or DNA
regions. While all the sequences may not be exactly alike, and may differ in one or
several bases, the sequences have a very similar structure, and implied common function.
Section: 4.5
46. What are the characteristics of Z-DNA and what does the Z in Z-DNA stand for?
Ans: Z-DNA is a double helix that is left-handed, in contrast with the right-handed screw
sense of the B-DNA helix. The phosphates in the backbone zigzagged; hence, they called
this new form Z-DNA.
Section: 4.2 and Figure 4.16
47. What are two features of mature eukaryotic mRNA that are unique as compared to prokaryotic
mRNA?
Ans: Eukaryotic mRNA has a special nucleotide “cap” at the 5' end and a poly A tail at the 3'
end.
Section: 4.5 and Figure 4.32
48. Why are deletion and insertion mutations potentially lethal?
Ans: The genetic code has no punctuation. The sequence of bases is read sequentially from a
fixed starting point codon, AUG. After the reading begins, every set of three bases codes
for one amino acid in the protein sequence. If an insertion or a deletion occurs, there can
be a completely different set of codes after the mutation which can result in a garbage
sequence and a nonfunctional protein.
Section: 4.6
49. What is an advantage of codon degeneracy?
Ans: Changes in the third position often have no effect on the final amino acid used in
translation. Thus, degeneracy minimizes the deleterious effect of DNA mutations. Also a
code without degeneracy would result in many codons encoding stop signals which
would also drastically increase the deleterious effects of mutations.
Section: 4.6
50. The genetic code is not universal. Where are exceptions found?
Ans: Exceptions are found in several places. The most notable are those in mitochondria and
ciliated protozoa.
Section: 4.6
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