BCH5413 EXAM 1QUESTIONS WITH CORRECT ANSWERS 2025.

BCH5413 EXAM 1QUESTIONS WITH
CORRECT ANSWERS 2025/2026
In the experiment described that supports DNA as the genetic material:
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Why does the mouse die if the researcher mixes the complete dead pathogenic strain with live
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non-
pathogenic strain bacteria and then inject it into the mouse? (The first mouse in the figure). -
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A
correct answersThe mouse dies because the R strain has been transformed and is now an S stra
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in, capable of producing the virulence factors that make the S strain deadly to mice. This is beca
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use as the pathogenic strain is killed, its DNA is released, and now floating freely can go into the
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R strain and transform it.
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In the experiment described that supports DNA as the genetic material:
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What was the only scenario in which the mouse lives? Why? -
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correct answersThe only scenario in which the mouse lives is when DNA is destroyed. This is be
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cause it's DNA that contains the genetic information that codes for the virulence factors that kill
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mice when they become infected.
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In DNA, C1 is bonded to...
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This is important because... -
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correct answersa nitrogenous base (adenine, guanine, cytosine, or thymine)
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Importance - this allows the nitrogenous bases to form hydrogen bonds (A-T, C-
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G) between the 5`-3` strand and the 3`-5` strand.
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In DNA, C2 is bonded to...
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This is important because... - correct answersH
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Importance - C2 does not have a hydroxyl group, which distinguishes it from RNA.
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In DNA, C3 is bonded to...
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This is important because... - correct answersOH
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,Importance - A




A
The C3 of one sugar forms a phosphodiester bond with the 5` phosphate of another sugar.
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In DNA, C4 is bonded to... - correct answersC5
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In DNA, C5 is bonded to...
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This is important because... - correct answersphosphate
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Importance - A




A
The C5 can be the lead sugar or form phosphodiester bonds with the C3 of a second sugar. This
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gives DNA the 5` to 3` linkage.
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Describe why DNA has directionality. - A A A A A




correct answersThe 5' end has a free phosphate group and 3' end has a free hydroxyl (OH) grou
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p. Nucleotide strands form hydrogen bonds between the nitrogenous base off the 1' Carbon. D
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NA is always synthesized in the 5'-to-
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3' direction, which means that nucleotides are added only to the 3' end of the growing strand. I
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n DNA, G forms 3 hydrogen bonds to C, A forms two hydrogen bonds to T.
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Sequence of DNA has an effect on the structure. A A A A A A A A




What is the meaning of the term antiparallel in the structure of DNA? -
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correct answersAntiparallel in the structure of DNA refers to how each strand of the double heli
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x is parallel to each other, but their orientation is opposite; their 5' -
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3' polarities are in opposite directions.
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5. What does the Meselson and Stahl experiment confirm? -
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A
correct answersIn 1958 Meselson and Stahl published their experiment of DNA replication in E
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scherichia coli. In this experiment they started their DNA molecule with heavy nitrogen bases a
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nd when they are separated the new strand made was with light nitrogen bases and the new da
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ughter strand each was found to have one heavy and one light strand which proved the DNA rep
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lication mechanism as semiconservative DNA replication model as proposed by Watson and Cri
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ck.

True/False: Most biological DNA is positively supercoiled. - A A A A A A A




correct answersFalse, Biological DNA is negatively supercoiled
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True/False: GC rich DNA has a lower melting temperature than AT rich DNA -
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correct answersFalse, GC rich DNA has a higher melting temperature because it forms 3 hydrog
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en bonds compared to the 2 hydrogen bonds by AT.
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, True/False: Chargaff's rule: A=G and T=C - correct answersFalse
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The rule is that DNA from any organism should have a stoichiometric relationship of 1:1 for pyri
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midines : purines or stated mathematically C + T (pyrimidines) = A + G (purines).
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The number of pyrimidines (C, T) however does not need to be equal (C=T), or purines for that
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matter.

True/False: Increased salt concentration increases the stability of complimentary base pairing -
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correct answersTrue
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Does A DNA or Z DNA have a right handed helix? - correct answersA DNA
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Does A DNA or Z DNA have 12 bp per turn? - correct answersZ DNA
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Is A DNA or Z DNA the dehydrated form? - correct answersA DNA
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Describe three differences between DNA and RNA. -
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correct answers1. The nitrogenous bases vary; for DNA the nitrogenous bases are Adenine, Thy
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mine, Guanine and Cytosine whereas RNA nitrogenous bases are Adenine, Uracil, Guanine, and
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Cytosine
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2. RNA has a hydroxyl group (-OH) on the 2' carbon of the 5-
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carbon sugar whereas DNA has a hydrogen (-
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H) (note: this is where the name *RIBOnucleic* acid and *DEOXYRIBOnucleic* acid comes from
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)

3. DNA is a double strand and has major and minor grooves whereas RNA is a single strand with
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only major grooves A A




Describe similarities between DNA and RNA. - A A A A A A




correct answers1. Both DNA and RNA are large biological polymers
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2. Both DNA and RNA are nucleic acids
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3.Both DNA and RNA consists of sugar, nitrogenous bases, and a phosphate backbone
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4. On both molecules Guanine pairs with Cytosine
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5. Both store genetic information
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What is the central dogma? Give two examples of RNAs that are exceptions to the central dogm
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a. Why are they exceptions? -
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correct answersCentral dogma can be stated as a DNA → RNA → protein pathway. Some viral R
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NA is the exception to it.
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One RNA virus encodes RNA-
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dependent RNA polymerases (RdRPs) to replicate and transcript based on the RNA template.
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