BCH5413 Exam 1 UPDATED ACTUAL
Exam Questions and CORRECT Answers
In the experiment described that supports DNA as the genetic material:
Why does the mouse die if the researcher mixes the complete dead pathogenic strain with live
non-pathogenic strain bacteria and then inject it into the mouse? (The first mouse in the figure). -
CORRECT ANSWER - The mouse dies because the R strain has been transformed and is
now an S strain, capable of producing the virulence factors that make the S strain deadly to mice.
This is because as the pathogenic strain is killed, its DNA is released, and now floating freely can
go into the R strain and transform it.
In the experiment described that supports DNA as the genetic material:
What was the only scenario in which the mouse lives? Why? - CORRECT 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... - CORRECT 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... - CORRECT 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... - CORRECT 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... - CORRECT ANSWER - C5
In DNA, C5 is bonded to...
This is important because... - CORRECT 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. - CORRECT 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? - CORRECT
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? - CORRECT 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. - CORRECT ANSWER -
False, Biological DNA is negatively supercoiled
True/False: GC rich DNA has a lower melting temperature than AT rich DNA - CORRECT
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 - CORRECT 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 -
CORRECT ANSWER - True
Does A DNA or Z DNA have a right handed helix? - CORRECT ANSWER - A DNA
Does A DNA or Z DNA have 12 bp per turn? - CORRECT ANSWER - Z DNA
Is A DNA or Z DNA the dehydrated form? - CORRECT ANSWER - A DNA
Describe three differences between DNA and RNA. - CORRECT 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
Exam Questions and CORRECT Answers
In the experiment described that supports DNA as the genetic material:
Why does the mouse die if the researcher mixes the complete dead pathogenic strain with live
non-pathogenic strain bacteria and then inject it into the mouse? (The first mouse in the figure). -
CORRECT ANSWER - The mouse dies because the R strain has been transformed and is
now an S strain, capable of producing the virulence factors that make the S strain deadly to mice.
This is because as the pathogenic strain is killed, its DNA is released, and now floating freely can
go into the R strain and transform it.
In the experiment described that supports DNA as the genetic material:
What was the only scenario in which the mouse lives? Why? - CORRECT 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... - CORRECT 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... - CORRECT 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... - CORRECT 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... - CORRECT ANSWER - C5
In DNA, C5 is bonded to...
This is important because... - CORRECT 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. - CORRECT 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? - CORRECT
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? - CORRECT 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. - CORRECT ANSWER -
False, Biological DNA is negatively supercoiled
True/False: GC rich DNA has a lower melting temperature than AT rich DNA - CORRECT
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 - CORRECT 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 -
CORRECT ANSWER - True
Does A DNA or Z DNA have a right handed helix? - CORRECT ANSWER - A DNA
Does A DNA or Z DNA have 12 bp per turn? - CORRECT ANSWER - Z DNA
Is A DNA or Z DNA the dehydrated form? - CORRECT ANSWER - A DNA
Describe three differences between DNA and RNA. - CORRECT 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
