ERT 101 Biochemistry
Tutorial – Nucleic acid
1. What structure do DNA nucleotides and RNA nucleotides have in common?
Both DNA and RNA nucleotides are each composed of a pentose sugar, a phosphate, and a
nitrogen base.
2. Compare between DNA and RNA
3. If a DNA sample contains 31% adenine, what is its complete percentage base composition?
Adenine = Thymine
Guanine = Cytosine
Adenine 31%, so Thymine also 31%
Guanine 18% and Cytosine 18%
4. Why is DNA replication termed ‘semiconservative’
‘Semiconservative’ refers to the fact that each of the daughter molecule retains one parental
strand and has one new strand; in other words, each is half new and half old.
5. Explain the principal and method in electrophoresis for DNA analysis
Gel electrophoresis separate nucleic acids on the basis of molecular weight and 3-D structure
in an electric field. The technique involves drawing DNA molecules, which have an overall
negative charge, through a semisolid gel by an electric current toward the positive electrode
within an electrophoresis chamber. The used gel is typically composed of a purified sugar
component of agar called agarose.
Electrophoresis method :
 Nucleuic acids mixture placed in well
 Nucleic acids are -ve charge (phosphate group)
 Nucleic acid migrate to anode
 Rate of migration are proportional to molecular size
6. If molecules of mRNA have the following nucleotide base sequences, what will be the sequence
of amino acids in polypeptides synthesized in eukaryotic ribosomes?
a. AUGGGGAUACGCUACCCC
b. CCGUACAUGCUAAUCCCU
c. CCGAUGUAACCUCGAUCC
d. AUGCGGUCAGCCCCGUGA
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a. Met-Gly-Ile-Arg-Tyr-Pro
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b. Pro-Tyr-Met-Leu-Ile-Pro
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c. Pro-Met-stop
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d. Met-Arg-Ser-Ala-Pro-stop, or SeCys
7. If a scientist synthesizes a DNA molecule with the nucleotide base sequence
TACGGGGGAGGGGGAGGGGGA and then uses it for transcription and translation, what
would be the amino acid sequence of the product?
TACGGGGGAGGGGGAGGGGGA – DNA base sequence
Use it for transcription, so RNA base sequence :
AUGCCCCCUCCCCCUCCCCCU
Use it for translation, so amino acid sequence would be :
Met-Pro-Pro-Pro-Pro-Pro-Pro
8. The amino acid for a short peptide is Lys-Thr-Ser-Arg-His-Val. With the aid of genetic code,
(i) What are the possible base sequences of the mRNA
(ii) What are the possible base sequences of the transcribed DNA strand code for the peptide?
(i)
5’-AAA-3’ ACU AGU AGA CAU GUU
AAG
ACC AGC AGG CAC GUC
ACA
ACG
(ii)
GUA
GUG
3’-TTT-5’ TGA TCA TCT GTA CAA
TTC
TGG TCG TCC GTG CAG
TGT
CAT
TGC
CAC
9. an mRNA contains the following translated sequence
CGAAUGCCCAUAGAUCGGAGU
i) deduce the amino acids that would result from this sequence
Arg-Met-Pro-Ile-Asp-Arg-Ser
ii) if the first A is deleted from sequence, what new amino acid sequence would result?
Arg-Cys-Pro-Stop
iii) Determine the type of mutations that have occurred in the following altered mRNA segment
CGAAUGGCCCAUAGAUCGGAGU
Insertion of new base; G. so it is a frameshift insertion mutation. New amino acid sequence is
Arg-Met-Ala-His-Arg-Ser-Glu.
10. Give definition about DNA replication, transcription and translation.

replication – DNA replication is an anabolic polymerization process, that allows a cell to pass
copies of its genome to its descendants. The key to DNA replication is the complementary structure of the two strands: Adenine and guanine in one strand bond with thymine and cytosine,
respectively, in the other. DNA replication is a simple concept - a cell separates the two
original strands and uses each as a template for the synthesis of a new complementary strand.
Biologists say that DNA replication is semiconservative because each daughter DNA molecule
is composed of one original strand and one new strand.
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Transcription – is a process of copying information coded in DNA to RNA copy of gene. Cells
do not transfer the information coded in DNA directly but first make an RNA copy of gene.
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Translation - Translation is the process whereby ribosomes use the genetic information of
nucleotide sequences to synthesize polypeptides composed of specific amino acid sequences.