BCH Exam 3 Past Qs
You repeat the classic Meselson and Stahl experiment in your advanced undergraduate biochemistry
laboratory course: growing the E. coli first in 15N-enriched media for one generation and then switching
over to 14N-enriched media. The ratio of 14N over 15N single stranded DNA in the second generation
after growth in 14N is:
a. 1:1 b. 3:1 c. 4:1 d. 7:1 e. 15:1 - correct answer ✔✔b. 3:1
During DNA replication, the lagging strand is complemented with Okazaki fragments that still contain the
RNA primer. Which pair of enzymes removes the RNA primer and seals the DNA nicks?
a. DNA polymerase I and helicase b. DNA polymerase I and ligase c. DNA polymerase I and primase d.
DNA polymerase III and helicase e. DNA polymerase III and primase - correct answer ✔✔b. DNA
polymerase I and ligase
Which of the following best describes the process of DNA replication in a prokaryote
a. replication begins at a unique site and proceeds in two directions, meeting about halfway around a
typically circular chromosome b. replication begins at a unique site and proceeds in one direction all the
way around a typically circular chromosome c. replication begins at a unique site and proceeds in two
directions, until the entire typically linear chromosome is replicated d. replication begins at multiple
sites, spreading outward until the entire typically circular chromosome is replicated e. replication begins
at multiple sites, spreading outward until the entire typically linear chromosome is replicated - correct
answer ✔✔a. replication begins at a unique site and proceeds in two directions, meeting about halfway
around a typically circular chromosome
Which of the following describes the general mechanism of DNA synthesis:
a. both strands are synthesied in a 5'→ 3' fashion, but one is discontinuous b. the strands become
separated during synthesis c. synthesis occurs in both directions from the starting site of synthesis (ori)
d. synthesis of DNA is a very accurate process e. all of these are correct - correct answer ✔✔e. all of
these are correct
Unwinding of double helical DNA during replication is coupled to the hydrolysis of ATP by which of the
following enzymes:
a) polymerase b) helicase c) primase d) ligase e) phosphatase - correct answer ✔✔b) helicase
, Exposure of double stranded DNA to UV light most commonly results in:
a. thymine dimerization b. depurinization c. base deamination d. base deletion e. base alkylation -
correct answer ✔✔a. thymine dimerization
Primases are enzymes that facilitate replication by:
a) synthesizing an oligo-RNA complimentary to the template b) melting double stranded DNA at the
origin of replication c) recruiting dNTPs to the RNA polymerase d) recruiting helicase to the replisome e)
recruiting DNA polymerase to the origin of replication - correct answer ✔✔a) synthesizing an oligo-RNA
complimentary to the template
When an error in DNA replication introduces a base-pair mismatch in a double-stranded DNA, the
methyl-directed repair system
a. corrects the DNA strand that is methylated b. corrects the mismatch by changing the template strand
c. corrects the mismatch by changing the newly replicated strand d. corrects the mismatch by
methylating uracil bases near the mismatch in the template strand e. corrects the mismatch by
methylating uracil bases near the mismatch in the newly replicated strand - correct answer ✔✔c.
corrects the mismatch by changing the newly replicated strand
The following generic scheme describes one step during DNA replication
NTP-(NMP)n + dNTP → NTP-(NMP)n-dNMP1 + PPi
This corresponds to:
a. the addition of the first nucleotide by the primase during primer synthesis b. the addition of the last
nucleotide by the primase during primer synthesis c. the addition of the first nucleotide by the DNA
polymerase d. the addition of the second nucleotide by the DNA polymerase e. DNA unwinding by DNA
gyrase - correct answer ✔✔c. the addition of the first nucleotide by the DNA polymerase
Which of the following statements is not correct?
a. an enhancer is a protein that binds to DNA to increase gene transcription b. inducer is typically a small
molecule that can induce gene expression by disabling a repressor c. when a repressor binds to an
operator site it inhibits transcription d. an operon may have many modes of regulation, but typically
contains only one promoter e. an enhancer is a DNA sequence located upstream the promoter region -
correct answer ✔✔a. an enhancer is a protein that binds to DNA to increase gene transcription
Which of the following is not true about the 𝜎 subunit (factor) of the RNA polymerase?
You repeat the classic Meselson and Stahl experiment in your advanced undergraduate biochemistry
laboratory course: growing the E. coli first in 15N-enriched media for one generation and then switching
over to 14N-enriched media. The ratio of 14N over 15N single stranded DNA in the second generation
after growth in 14N is:
a. 1:1 b. 3:1 c. 4:1 d. 7:1 e. 15:1 - correct answer ✔✔b. 3:1
During DNA replication, the lagging strand is complemented with Okazaki fragments that still contain the
RNA primer. Which pair of enzymes removes the RNA primer and seals the DNA nicks?
a. DNA polymerase I and helicase b. DNA polymerase I and ligase c. DNA polymerase I and primase d.
DNA polymerase III and helicase e. DNA polymerase III and primase - correct answer ✔✔b. DNA
polymerase I and ligase
Which of the following best describes the process of DNA replication in a prokaryote
a. replication begins at a unique site and proceeds in two directions, meeting about halfway around a
typically circular chromosome b. replication begins at a unique site and proceeds in one direction all the
way around a typically circular chromosome c. replication begins at a unique site and proceeds in two
directions, until the entire typically linear chromosome is replicated d. replication begins at multiple
sites, spreading outward until the entire typically circular chromosome is replicated e. replication begins
at multiple sites, spreading outward until the entire typically linear chromosome is replicated - correct
answer ✔✔a. replication begins at a unique site and proceeds in two directions, meeting about halfway
around a typically circular chromosome
Which of the following describes the general mechanism of DNA synthesis:
a. both strands are synthesied in a 5'→ 3' fashion, but one is discontinuous b. the strands become
separated during synthesis c. synthesis occurs in both directions from the starting site of synthesis (ori)
d. synthesis of DNA is a very accurate process e. all of these are correct - correct answer ✔✔e. all of
these are correct
Unwinding of double helical DNA during replication is coupled to the hydrolysis of ATP by which of the
following enzymes:
a) polymerase b) helicase c) primase d) ligase e) phosphatase - correct answer ✔✔b) helicase
, Exposure of double stranded DNA to UV light most commonly results in:
a. thymine dimerization b. depurinization c. base deamination d. base deletion e. base alkylation -
correct answer ✔✔a. thymine dimerization
Primases are enzymes that facilitate replication by:
a) synthesizing an oligo-RNA complimentary to the template b) melting double stranded DNA at the
origin of replication c) recruiting dNTPs to the RNA polymerase d) recruiting helicase to the replisome e)
recruiting DNA polymerase to the origin of replication - correct answer ✔✔a) synthesizing an oligo-RNA
complimentary to the template
When an error in DNA replication introduces a base-pair mismatch in a double-stranded DNA, the
methyl-directed repair system
a. corrects the DNA strand that is methylated b. corrects the mismatch by changing the template strand
c. corrects the mismatch by changing the newly replicated strand d. corrects the mismatch by
methylating uracil bases near the mismatch in the template strand e. corrects the mismatch by
methylating uracil bases near the mismatch in the newly replicated strand - correct answer ✔✔c.
corrects the mismatch by changing the newly replicated strand
The following generic scheme describes one step during DNA replication
NTP-(NMP)n + dNTP → NTP-(NMP)n-dNMP1 + PPi
This corresponds to:
a. the addition of the first nucleotide by the primase during primer synthesis b. the addition of the last
nucleotide by the primase during primer synthesis c. the addition of the first nucleotide by the DNA
polymerase d. the addition of the second nucleotide by the DNA polymerase e. DNA unwinding by DNA
gyrase - correct answer ✔✔c. the addition of the first nucleotide by the DNA polymerase
Which of the following statements is not correct?
a. an enhancer is a protein that binds to DNA to increase gene transcription b. inducer is typically a small
molecule that can induce gene expression by disabling a repressor c. when a repressor binds to an
operator site it inhibits transcription d. an operon may have many modes of regulation, but typically
contains only one promoter e. an enhancer is a DNA sequence located upstream the promoter region -
correct answer ✔✔a. an enhancer is a protein that binds to DNA to increase gene transcription
Which of the following is not true about the 𝜎 subunit (factor) of the RNA polymerase?
