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