1
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Mammalian Genetics BCH5413 Exam 4
Questions and Answers (100% Correct
Answers) Already Graded A+
What is the central dogma of molecular biology?— Ans: DNA
can be both replicated and transcribed into mRNA, which can be
translated into protein
T/F: the addition of bulky aromatic rings and/or exposure to UV
© 2025 Assignment Expert
light can cause the DNA to "bubble."— Ans: True (this is due to
intrastrand crosslinking, in which adjacent nucleotides basepair,
causing bubbling)
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T/F: chemotherapy can cause both single and double-stranded
breaks in DNA.— Ans: True
Why is it very important that damaged DNA is repaired?— Ans:
Damaged DNA can lead to incorrect base pairing, which can
lead to mutations (permanent changes in the DNA sequence)
What is 8-oxyguanine?— Ans: Guanine with a new -C=O bond in
place of the original =C-H2 bond
What happens to GC base pairing when guanine is converted to
8-oxyguanine?— Ans: 8-oxyguanine flips over, causing it to
hydrogen bond with adenine (instead of cytosine) and become a
thymine in the next round of DNA replication
How many hydrogen bonds does 8-oxyguanine have with its
partner nucleotide?— Ans: 2 (instead of guanine's normal 3)
What is cisplatin?— Ans: An agent used in chemotherapy that
has lots of bulky side chains
What type of DNA damage can be caused by cisplatin?— Ans:
Bulky adducts (DNA "bubbles") caused by the addition of large
sidechains and/or intrastrand crosslinking caused by cisplatin
binding to 2 adjacent guanines
, 2
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Why is cisplatin an effective treatment for cancer?— Ans: The
addition of cisplatin causes damage to DNA, so introducing it to
cancer cells can help damage/kill them
What type of mutation occurs when a single basepair is changed,
but the amino acid stays the same?— Ans: Silent mutation
What type of mutation occurs when a single basepair is changed,
changing the amino acid?— Ans: Missense mutation
What type of mutation occurs when a single basepair is changed,
causing the formation of a stop codon?— Ans: Nonsense
mutation
T/F: mutations in any part of a protein's sequence can be equally
© 2025 Assignment Expert
damaging.— Ans: False (mutations in the active site are more
detrimental than mutations in outer regions of the protein)
What type of mutation occurs when a single basepair is inserted or
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deleted?— Ans: Frameshift mutation
What kind of DNA damage is recognized by the BER repair
proteins?— Ans: A single-stranded break in the DNA
Why is it necessary to have multiple types of glycosylases?— Ans:
Each type of glycosylase recognizes a different type of DNA
damage
How does BER differ if a mono-functional vs. a bi-functional
glycosylase is used?— Ans: Mono-functional glycosylases will only
cleave an incorrect base; bi-functional glycosylases will cleave
both an incorrect base and the DNA's backbone
T/F: "Short-patch" DNA repair refers to multiple bases being
removed and replaced along a short section of DNA.— Ans:
False ("short-patch" DNA repair is when only 1 base is removed
and replaced)
What is the additional enzyme that's required for "long-patch" DNA
repair before ligase can seal up the nick?— Ans: FEN1 (cleaves
the "flap" of incorrect bases)
, 3
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What are the 2 functions of APE1?— Ans: (1) To cut the DNA
backbone at the 5' end; (2) to proofread for mistakes by DNAP-
beta
Functions of APE1 experiment: why is only 1 short band visible in
the control lane?— Ans: No ligase has been added, so the
fragments are not able to be connected, giving the short band
only (21 bp)
Functions of APE1 experiment: how does the short band become
a long band (21 bp -> 40 bp)?— Ans: DNA ligase is added,
causing the 2 fragments to be connected and be located higher
on the gel (40 bp)
© 2025 Assignment Expert
Functions of APE1 experiment: why does adding ligase to lane 3
(correct A/T pairing) cause robust formation of the long band
while adding ligase to lane 8 (G/T mismatch) only results in a small
amount of the long band?— Ans: If the base pairing before a
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nick is CORRECT, ligase can easily seal it back up; if the base
pairing before a nick is a MISMATCH, ligase requires the help of
APE1 and DNAP-beta to efficiently seal the nick (low efficiency if
ligase acts alone)
Functions of APE1 experiment: why does the addition of DNAP-
beta in lane 9 not improve the efficiency of forming the long
band?— Ans: DNAP-beta is not able to remove the incorrect
base pair before replacing it, as it requires APE1 to do so
Functions of APE1 experiment: why does the addition of APE1 in
lane 10 improve the efficiency of long band formation?— Ans:
APE1 is able to remove the mismatched base pair, allowing DNAP-
beta to easily add a new base and ligase to seal the nick
T/F: the more APE1 added to nicked DNA, the more efficient the
ligation is.— Ans: True (ligation efficiency is dependent on APE1
concentration)
T/F: ligation after DNA repair can be efficient without APE1 (only
with ligase and DNAP-beta).— Ans: False (APE1 is required for
efficient ligation)
, 4
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Why are there a wide variety of consequences if BER enzymes are
defective?— Ans: Since glycosylases target many different types
of DNA damage, having certain ones be defective can result in
many different consequences
What kind of DNA damage is recognized by the NER repair
proteins?— Ans: Bulky adducts in DNA ("bubbles" caused by
intrastrand crosslinking)
What is the basic difference between the GG-NER pathway and
the TC-NER pathway?— Ans: GG-NER is for inactive genes while
TC-NER is for genes being actively transcribed
T/F: oligonucleotide excision is the same as "long-patch" DNA
© 2025 Assignment Expert
repair.— Ans: False (oligonucleotide excision involves a long
piece of damaged DNA being removed, while "long-patch" DNA
repair involves only removing a few bases)
GG-NER: how does XPC become stabilized at typical DNA
Guru01 - Stuvia
damage by bulky adducts?— Ans: It uses its beta-sheet "finger"
to flip the 2 correct bases (across from the dimerized bases) out of
the helix, allowing it to stabilize and act as a scaffold for other
proteins
T/F: DNA glycosylases and XPC both flip the damaged bases out
of the helix for removal.— Ans: False (while DNA glycosylases flip
out the damaged base for removal, XPC flips out the CORRECT
bases that are across from the dimerized bases)
GG-NER: how does XPC become stabilized at harder-to-detect
DNA damage (extra bulky adducts)?— Ans: XPC requires the
help of DDB (damaged DNA-binding) protein to flip out the
correct bases and stabilize
TC-NER: how does the DNA damage get recognized?— Ans:
During transcription, RNAP will automatically stall at areas of DNA
damage
TC-NER: what is the function of CSB in the process of repair?—
Ans: CSB binds to stalled RNAP and helps recruit both CSA and
UVSSA
For Expert help and assignment solutions, +254707240657
Mammalian Genetics BCH5413 Exam 4
Questions and Answers (100% Correct
Answers) Already Graded A+
What is the central dogma of molecular biology?— Ans: DNA
can be both replicated and transcribed into mRNA, which can be
translated into protein
T/F: the addition of bulky aromatic rings and/or exposure to UV
© 2025 Assignment Expert
light can cause the DNA to "bubble."— Ans: True (this is due to
intrastrand crosslinking, in which adjacent nucleotides basepair,
causing bubbling)
Guru01 - Stuvia
T/F: chemotherapy can cause both single and double-stranded
breaks in DNA.— Ans: True
Why is it very important that damaged DNA is repaired?— Ans:
Damaged DNA can lead to incorrect base pairing, which can
lead to mutations (permanent changes in the DNA sequence)
What is 8-oxyguanine?— Ans: Guanine with a new -C=O bond in
place of the original =C-H2 bond
What happens to GC base pairing when guanine is converted to
8-oxyguanine?— Ans: 8-oxyguanine flips over, causing it to
hydrogen bond with adenine (instead of cytosine) and become a
thymine in the next round of DNA replication
How many hydrogen bonds does 8-oxyguanine have with its
partner nucleotide?— Ans: 2 (instead of guanine's normal 3)
What is cisplatin?— Ans: An agent used in chemotherapy that
has lots of bulky side chains
What type of DNA damage can be caused by cisplatin?— Ans:
Bulky adducts (DNA "bubbles") caused by the addition of large
sidechains and/or intrastrand crosslinking caused by cisplatin
binding to 2 adjacent guanines
, 2
For Expert help and assignment solutions, +254707240657
Why is cisplatin an effective treatment for cancer?— Ans: The
addition of cisplatin causes damage to DNA, so introducing it to
cancer cells can help damage/kill them
What type of mutation occurs when a single basepair is changed,
but the amino acid stays the same?— Ans: Silent mutation
What type of mutation occurs when a single basepair is changed,
changing the amino acid?— Ans: Missense mutation
What type of mutation occurs when a single basepair is changed,
causing the formation of a stop codon?— Ans: Nonsense
mutation
T/F: mutations in any part of a protein's sequence can be equally
© 2025 Assignment Expert
damaging.— Ans: False (mutations in the active site are more
detrimental than mutations in outer regions of the protein)
What type of mutation occurs when a single basepair is inserted or
Guru01 - Stuvia
deleted?— Ans: Frameshift mutation
What kind of DNA damage is recognized by the BER repair
proteins?— Ans: A single-stranded break in the DNA
Why is it necessary to have multiple types of glycosylases?— Ans:
Each type of glycosylase recognizes a different type of DNA
damage
How does BER differ if a mono-functional vs. a bi-functional
glycosylase is used?— Ans: Mono-functional glycosylases will only
cleave an incorrect base; bi-functional glycosylases will cleave
both an incorrect base and the DNA's backbone
T/F: "Short-patch" DNA repair refers to multiple bases being
removed and replaced along a short section of DNA.— Ans:
False ("short-patch" DNA repair is when only 1 base is removed
and replaced)
What is the additional enzyme that's required for "long-patch" DNA
repair before ligase can seal up the nick?— Ans: FEN1 (cleaves
the "flap" of incorrect bases)
, 3
For Expert help and assignment solutions, +254707240657
What are the 2 functions of APE1?— Ans: (1) To cut the DNA
backbone at the 5' end; (2) to proofread for mistakes by DNAP-
beta
Functions of APE1 experiment: why is only 1 short band visible in
the control lane?— Ans: No ligase has been added, so the
fragments are not able to be connected, giving the short band
only (21 bp)
Functions of APE1 experiment: how does the short band become
a long band (21 bp -> 40 bp)?— Ans: DNA ligase is added,
causing the 2 fragments to be connected and be located higher
on the gel (40 bp)
© 2025 Assignment Expert
Functions of APE1 experiment: why does adding ligase to lane 3
(correct A/T pairing) cause robust formation of the long band
while adding ligase to lane 8 (G/T mismatch) only results in a small
amount of the long band?— Ans: If the base pairing before a
Guru01 - Stuvia
nick is CORRECT, ligase can easily seal it back up; if the base
pairing before a nick is a MISMATCH, ligase requires the help of
APE1 and DNAP-beta to efficiently seal the nick (low efficiency if
ligase acts alone)
Functions of APE1 experiment: why does the addition of DNAP-
beta in lane 9 not improve the efficiency of forming the long
band?— Ans: DNAP-beta is not able to remove the incorrect
base pair before replacing it, as it requires APE1 to do so
Functions of APE1 experiment: why does the addition of APE1 in
lane 10 improve the efficiency of long band formation?— Ans:
APE1 is able to remove the mismatched base pair, allowing DNAP-
beta to easily add a new base and ligase to seal the nick
T/F: the more APE1 added to nicked DNA, the more efficient the
ligation is.— Ans: True (ligation efficiency is dependent on APE1
concentration)
T/F: ligation after DNA repair can be efficient without APE1 (only
with ligase and DNAP-beta).— Ans: False (APE1 is required for
efficient ligation)
, 4
For Expert help and assignment solutions, +254707240657
Why are there a wide variety of consequences if BER enzymes are
defective?— Ans: Since glycosylases target many different types
of DNA damage, having certain ones be defective can result in
many different consequences
What kind of DNA damage is recognized by the NER repair
proteins?— Ans: Bulky adducts in DNA ("bubbles" caused by
intrastrand crosslinking)
What is the basic difference between the GG-NER pathway and
the TC-NER pathway?— Ans: GG-NER is for inactive genes while
TC-NER is for genes being actively transcribed
T/F: oligonucleotide excision is the same as "long-patch" DNA
© 2025 Assignment Expert
repair.— Ans: False (oligonucleotide excision involves a long
piece of damaged DNA being removed, while "long-patch" DNA
repair involves only removing a few bases)
GG-NER: how does XPC become stabilized at typical DNA
Guru01 - Stuvia
damage by bulky adducts?— Ans: It uses its beta-sheet "finger"
to flip the 2 correct bases (across from the dimerized bases) out of
the helix, allowing it to stabilize and act as a scaffold for other
proteins
T/F: DNA glycosylases and XPC both flip the damaged bases out
of the helix for removal.— Ans: False (while DNA glycosylases flip
out the damaged base for removal, XPC flips out the CORRECT
bases that are across from the dimerized bases)
GG-NER: how does XPC become stabilized at harder-to-detect
DNA damage (extra bulky adducts)?— Ans: XPC requires the
help of DDB (damaged DNA-binding) protein to flip out the
correct bases and stabilize
TC-NER: how does the DNA damage get recognized?— Ans:
During transcription, RNAP will automatically stall at areas of DNA
damage
TC-NER: what is the function of CSB in the process of repair?—
Ans: CSB binds to stalled RNAP and helps recruit both CSA and
UVSSA
