First Exam Graded

Question 1

Which of the following deoxyoligonucleotides will hybridize with a DNA containing the sequence (5’)AGACTGGTC(3’)?
A) (5’)CTCATTGAG(3’)
B) (5’)GACCAGTCT(3’)
C) (5’)GAGTCAACT(3’)
D) (5’)TCTGACCAG(3’)
E) (5’)TCTGGATCT(3’)

Answer 1

B) (5’)GACCAGTCT(3’)

Question 2

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’ Phosphate of the next.

Answer 2

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

Question 3

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 3

E) A + G = T + C.

Question 4

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 4

D) right; 20; 3.4

Question 5

5. Which of the following are possible base compositions for single-stranded RNA?
   %A %G %C %T %U
   A) 5 45 45 0 5
   B) 25 25 25 0 25
   C) 35 10 30 0 25
   D) All of the above
   E) None of the above

Answer 5

D) All of the above

Question 6

n 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 6

E) All of the above.

Question 7

The most precise modern definition of a gene is a segment of genetic material that:
A) codes for one polypeptide.
B) codes for one polypeptide or RNA product.
C) determines one phenotype.
D) determines one trait.
E) codes for one protein

Answer 7

B) codes for one polypeptide or RNA product.

Question 8

ntrons:
A) are frequently present in prokaryotic genes but are rare in eukaryotic genes.
B) are spliced out before transcription.
C) are translated but not transcribed.
D) can occur many times within a single gene.
E) encode unusual amino acids in proteins

Answer 8

D) can occur many times within a single gene.

Question 8

The DNA in a bacterial (prokaryotic) chromosome is best described as:
A) a single circular double-helical molecule.
B) a single linear double-helical molecule.
C) a single linear single-stranded molecule.
D) multiple linear double-helical molecules.
E) multiple linear single-stranded molecules

Answer 8

A) a single circular double-helical molecule.

Question 9

The DNA in a eukaryotic chromosome is best described as:
A) a single circular double-helical molecule.
B) a single linear double-helical molecule.
C) a single linear single-stranded molecule.
D) multiple linear double-helical molecules.
E) multiple linear single-stranded molecules.

Answer 9

B) a single linear double-helical molecule.

Question 10

Which of the following does not contribute to the octameric histone core?
A) H1
B) H2A
C) H2B
D) H3
E) H4

Answer 10

A) H1

Question 11

The fundamental repeating unit of organization in a eukaryotic chromosome is the:
A) centrosome.
B) lysosome.
C) microsome.
D) nucleosome.
E) polysome.

Answer 11

D) nucleosome.

Question 12

When a DNA molecule is described as replicating bidirectionally, that means that it has two:
A) chains.
B) independently replicating segment.
C) origins.
D) replication forks.
E) termination points

Answer 12

D) replication forks.

Question 13

An Okazaki fragment is a:
A) fragment of DNA resulting from endonuclease action.
B) fragment of RNA that is a subunit of the 30S ribosome.
C) piece of DNA that is synthesized in the 3’ Æ 5’ direction.
D) segment of DNA that is an intermediate in the synthesis of the lagging strand.
E) segment of mRNA synthesized by RNA polymerase.

Answer 13

D) segment of DNA that is an intermediate in the synthesis of the lagging strand.

Question 13

he fundamental repeating unit of organization in a eukaryotic chromosome is the:
A) centrosome.
B) lysosome.
C) microsome.
D) nucleosome.
E) polysome.

Answer 13

D) nucleosome.

Question 14

Prokaryotic DNA polymerase III:
A) contains a 5’ -> 3’ proofreading activity to improve the fidelity of replication.
B) does not require a primer molecule to initiate replication.
C) has a b subunit that acts as a circular clamp to improve the processivity of DNA synthesis.
D) synthesizes DNA in the 3’ -> 5’ direction.
E) synthesizes only the leading strand; DNA polymerase I synthesizes the lagging strand.

Answer 14

C) has a b subunit that acts as a circular clamp to improve the processivity of DNA synthesis.

Question 15

In contrast to bacteria, eukaryotic chromosomes need multiple DNA replication origins
because:
A) eukaryotic chromosomes cannot usually replicate bidirectionally.
B) eukaryotic genomes are not usually circular, like the bacterial chromosome is.
C) the processivity of the eukaryotic DNA polymerase is much less than the bacterial enzyme.
D) their replication rate is much slower, and it would take too long with only a single origin per
chromosome.
E) they have a variety of DNA polymerases for different purposes, and need a corresponding
variety of replication origins.

Answer 15

D) their replication rate is much slower, and it would take too long with only a single origin per
chromosome.

Question 16

Which of these enzymes is not directly involved in methyl-directed mismatch repair in E.
coli?
A) DNA glycosylase
B) DNA helicase II
C) DNA ligase
D) DNA polymerase III
E) Exonuclease I

Answer 16

A) DNA glycosylase

Question 17

In homologous genetic recombination, RecA protein is involved in:
A) Strand invasion to form a Holliday intermediates.
B) introduction of negative supercoils into the recombination products.
C) nicking the two duplex DNA molecules to initiate the reaction.
D) pairing a DNA strand from one duplex DNA molecule with sequences in another duplex,
regardless of complementarity.
E) resolution of the Holliday intermediate

Answer 17

A) Strand invasion to form a Holliday intermediates.

Question 18

Type of bond with role:
(a) phosphodiester
(b) N-glycosidic
(c) phosphate ester
(d) hydrogen

1.___ links base to pentose in nucleotide
2. ___ joins adjacent nucleotides in one strand
3.___ joins complementary nucleotides in two strands
4.___ difference between a nucleoside and a nucleotide

Answer 18

1. b
2. a
3. d
4. c

Question 19

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

Answer 19

3.4 Å * 10,000 = 34,000 Å = 3.4 μm.

Question 20

On the strand synthesized discontinuously, the short
pieces are called (d) ____________ fragments. An RNA primer for each of the fragments is
synthesized by an enzyme called (e) __________,

Answer 20

d: Okazaki
e: primase

Question 20

DNA replication in E. coli begins at a site in the DNA called the (a) ___________. At the
replication fork the (b) ___________ strand is synthesized continuously while the (c) _________
strand is synthesized discontinuously.

Answer 20

a: origin
b:leading
c:lagging

Question 21

This RNA primer is removed after the
fragment is synthesized by the enzyme (f) ___________, using its (g) _____________ activity.
The nicks left behind in this process are sealed by the enzyme (h) _____________.

Answer 21

f: DNA polymerase I
g: 5’->3’exonculase
h: DNA ligase

Question 22

What repair systems exist, When There Is No Undamaged DNA to Use as a Template for Repair?

Answer 22

Homologous repair, Nonhomologous end loining (NHEJ), translesion synthesis (Error-
prone)

Question 23

What are the 4 steps in Homologous RecombinaIon?

Answer 23

1, 5’-end processing.
2, Strand invasion.
3, Branch migraIon.
4, Holliday intermediate resoluIon and ligaIon.

Question 24

What is the key difference between HR and NHEJ?

Answer 24

HR involve used another Chromosome to synthesis DNA, but NHEJ does not have this step

Question 25

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 25

n 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

Question 26

Describe the composition and structure of a nucleosome.

Answer 26

consists of 146 base pairs of double-stranded DNA wrapped in a supercoil around a core of histones and 52 base pairs of linking
DNA.
contains two copies each of histones H2A, H2B, H3, and H4.