BCH 5413 UPDATED ACTUAL QUESTIONS
AND CORRECT ANSWERS
COMPREHENSIVE STUDY GUIDE
●● In the experiment described that supports DNA as the genetic
material:
What was the only scenario in which the mouse lives? Why?
Answer: The only scenario in which the mouse lives is when DNA is
destroyed. This is because it's DNA that contains the genetic information
that codes for the virulence factors that kill mice when they become
infected.
●● In DNA, C1 is bonded to...
This is important because...
Answer: a nitrogenous base (adenine, guanine, cytosine, or thymine)
Importance - this allows the nitrogenous bases to form hydrogen bonds
(A-T, C-G) between the 5`-3` strand and the 3`-5` strand.
●● In DNA, C2 is bonded to...
This is important because...
,Answer: H
Importance - C2 does not have a hydroxyl group, which distinguishes it
from RNA.
●● In DNA, C3 is bonded to...
This is important because...
Answer: OH
Importance - The C3 of one sugar forms a phosphodiester bond with the
5` phosphate of another sugar.
●● In DNA, C4 is bonded to...
Answer: C5
●● In DNA, C5 is bonded to...
This is important because...
Answer: phosphate
Importance - The C5 can be the lead sugar or form phosphodiester bonds
with the C3 of a second sugar. This gives DNA the 5` to 3` linkage.
,●● Describe why DNA has directionality.
Answer: The 5' end has a free phosphate group and 3' end has a free
hydroxyl (OH) group. Nucleotide strands form hydrogen bonds between
the nitrogenous base off the 1' Carbon. DNA is always synthesized in the
5'-to-3' direction, which means that nucleotides are added only to the 3'
end of the growing strand. In DNA, G forms 3 hydrogen bonds to C, A
forms two hydrogen bonds to T.
Sequence of DNA has an effect on the structure.
●● What is the meaning of the term antiparallel in the structure of
DNA?
Answer: Antiparallel in the structure of DNA refers to how each strand
of the double helix is parallel to each other, but their orientation is
opposite; their 5' - 3' polarities are in opposite directions.
●● 5. What does the Meselson and Stahl experiment confirm?
Answer: In 1958 Meselson and Stahl published their experiment of DNA
replication in Escherichia coli. In this experiment they started their DNA
molecule with heavy nitrogen bases and when they are separated the
new strand made was with light nitrogen bases and the new daughter
strand each was found to have one heavy and one light strand which
proved the DNA replication mechanism as semiconservative DNA
replication model as proposed by Watson and Crick.
, ●● True/False: Most biological DNA is positively supercoiled.
Answer: False, Biological DNA is negatively supercoiled
●● True/False: GC rich DNA has a lower melting temperature than AT
rich DNA
Answer: False, GC rich DNA has a higher melting temperature because
it forms 3 hydrogen bonds compared to the 2 hydrogen bonds by AT.
●● True/False: Chargaff's rule: A=G and T=C
Answer: False
The rule is that DNA from any organism should have a stoichiometric
relationship of 1:1 for pyrimidines : purines or stated mathematically C
+ T (pyrimidines) = A + G (purines).
The number of pyrimidines (C, T) however does not need to be equal
(C=T), or purines for that matter.
●● True/False: Increased salt concentration increases the stability of
complimentary base pairing
Answer: True
●● Does A DNA or Z DNA have a right handed helix?
Answer: A DNA
●● Does A DNA or Z DNA have 12 bp per turn?
AND CORRECT ANSWERS
COMPREHENSIVE STUDY GUIDE
●● In the experiment described that supports DNA as the genetic
material:
What was the only scenario in which the mouse lives? Why?
Answer: The only scenario in which the mouse lives is when DNA is
destroyed. This is because it's DNA that contains the genetic information
that codes for the virulence factors that kill mice when they become
infected.
●● In DNA, C1 is bonded to...
This is important because...
Answer: a nitrogenous base (adenine, guanine, cytosine, or thymine)
Importance - this allows the nitrogenous bases to form hydrogen bonds
(A-T, C-G) between the 5`-3` strand and the 3`-5` strand.
●● In DNA, C2 is bonded to...
This is important because...
,Answer: H
Importance - C2 does not have a hydroxyl group, which distinguishes it
from RNA.
●● In DNA, C3 is bonded to...
This is important because...
Answer: OH
Importance - The C3 of one sugar forms a phosphodiester bond with the
5` phosphate of another sugar.
●● In DNA, C4 is bonded to...
Answer: C5
●● In DNA, C5 is bonded to...
This is important because...
Answer: phosphate
Importance - The C5 can be the lead sugar or form phosphodiester bonds
with the C3 of a second sugar. This gives DNA the 5` to 3` linkage.
,●● Describe why DNA has directionality.
Answer: The 5' end has a free phosphate group and 3' end has a free
hydroxyl (OH) group. Nucleotide strands form hydrogen bonds between
the nitrogenous base off the 1' Carbon. DNA is always synthesized in the
5'-to-3' direction, which means that nucleotides are added only to the 3'
end of the growing strand. In DNA, G forms 3 hydrogen bonds to C, A
forms two hydrogen bonds to T.
Sequence of DNA has an effect on the structure.
●● What is the meaning of the term antiparallel in the structure of
DNA?
Answer: Antiparallel in the structure of DNA refers to how each strand
of the double helix is parallel to each other, but their orientation is
opposite; their 5' - 3' polarities are in opposite directions.
●● 5. What does the Meselson and Stahl experiment confirm?
Answer: In 1958 Meselson and Stahl published their experiment of DNA
replication in Escherichia coli. In this experiment they started their DNA
molecule with heavy nitrogen bases and when they are separated the
new strand made was with light nitrogen bases and the new daughter
strand each was found to have one heavy and one light strand which
proved the DNA replication mechanism as semiconservative DNA
replication model as proposed by Watson and Crick.
, ●● True/False: Most biological DNA is positively supercoiled.
Answer: False, Biological DNA is negatively supercoiled
●● True/False: GC rich DNA has a lower melting temperature than AT
rich DNA
Answer: False, GC rich DNA has a higher melting temperature because
it forms 3 hydrogen bonds compared to the 2 hydrogen bonds by AT.
●● True/False: Chargaff's rule: A=G and T=C
Answer: False
The rule is that DNA from any organism should have a stoichiometric
relationship of 1:1 for pyrimidines : purines or stated mathematically C
+ T (pyrimidines) = A + G (purines).
The number of pyrimidines (C, T) however does not need to be equal
(C=T), or purines for that matter.
●● True/False: Increased salt concentration increases the stability of
complimentary base pairing
Answer: True
●● Does A DNA or Z DNA have a right handed helix?
Answer: A DNA
●● Does A DNA or Z DNA have 12 bp per turn?
