BCH5413 Exam A+ Questions and Answers Verified Solutions Latest Update 2026/2027

BCH5413 Exam A+ Questions and
Answers Verified Solutions Latest Update
2026/2027

Question:
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.


Question:
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.


Question:
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.


Question:
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.


Question:
In DNA, C4 is bonded to...

Answer:
C5


Question:
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.


Question:
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.


Question:
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.


Question:
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.


Question:
True/False: Most biological DNA is positively supercoiled.

Answer:
False, Biological DNA is negatively supercoiled


Question:
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.


Question:
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.

, Question:
True/False: Increased salt concentration increases the stability of complimentary base pairing

Answer:
True


Question:
Does A DNA or Z DNA have a right handed helix?

Answer:
A DNA


Question:
Does A DNA or Z DNA have 12 bp per turn?

Answer:
Z DNA


Question:
Is A DNA or Z DNA the dehydrated form?

Answer:
A DNA


Question:
Describe three differences between DNA and RNA.

Answer:
1. The
nitrogenous bases vary; for DNA the nitrogenous bases are Adenine,
Thymine, Guanine and Cytosine whereas RNA nitrogenous bases are Adenine, Uracil, Guanine,
and Cytosine
2. RNA has a hydroxyl group (-OH) on the 2' carbon of the 5-carbon