Download end of semester main examination

Reg. No:…………………………….
KIGALI INSTITUTE OF SCIENCE AND TECHNOLOGY
INSTITUT DES SCIENCES ET TECHNOLOGIE
Avenue de l'Armée, B.P. 3900 Kigali, Rwanda
INSTITUTE EXAMINATIONS – ACADEMIC YEAR 2012/2013
END OF SEMESTER MAIN EXAMINATION
FACULTY OF SCIENCE
SCIENCE-4-CHEMISTRY
THIRD YEAR-BIOCHEMISTRY, SEMESTER II
CHE 3314 MOLECULAR BIOLOGY
DATE: 24/04/2013
TIME: 2 HOURS
MAXIMUM MARKS = 60
INSTRUCTIONS
1. This paper contains TWO sections.
2. Answer Question ONE in Section A, and any TWO out of THREE
questions in Section B.
3. No written materials allowed into the examination room.
4. Write all answers in the booklet provided.
5. Do not forget to write your Registration Number.
6. All Questions carry a maximum of 20 Marks each.
7. Do not write any answers on this questions paper.
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SECTION A
1.
A. What are hairpins and how do they form? [2 mark]
B. Explain briefly three main stages of bacterial transcription. [4 marks]
C. Using the genetic code given below, give the amino acids specified by the
bacterial mRNA sequences and indicate the amino and carboxyl ends of the
polypeptide produced.
i.
5´–AUGUUUAAAUUUAAAUUUUGA–3´ [2 marks]
ii.
5´–AUGUAUAUAUAUAUAUGA–3´ [2 marks]
iii.
5´–AUGGAUGAAAGAUUUCUCGCUUGA–3´ [2 marks]
iv.
5´–AUGGGUUAGGGGACAUCAUUUUGA–3´ [2 marks]
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D. Each nucleotide pair of a DNA double helix weighs about 1 × 10–21 g. The
human body contains approximately 0.5 g of DNA.
i.
How many nucleotide pairs of DNA are in the human body? [1.5 marks]
ii.
If you assume that all the DNA in human cells is in the B-DNA form (DNA
that is in B form has an average distance of 0.34 nm between each nucleotide
pair), how far would the DNA reach if stretched end to end? [1.5 marks]
E. Briefly describe the structure of bacterial RNA polymerase. [3 marks]
SECTION B
2.
A. Researchers have proposed that early life on Earth used RNA as its source of
genetic information and that DNA eventually replaced RNA as the source of
genetic information. What aspects of DNA structure might make it better suited
than RNA to be the genetic material? [5 marks]
B. List all the components required for bacterial DNA replication and describe their
function. [8 Marks]
C.
i.
What is the 5’ cap? [1 mark]
ii.
How is the 5’ cap added to eukaryotic pre-mRNA? [3 marks]
iii.
What is the function of the 5’ cap? [3 marks]
3.
A. The following diagram represents a transcription unit in a hypothetical DNA
molecule:
i.
On the basis of the information given, is this DNA from a bacterium or
from a eukaryotic organism? Explain your answer. [3 Marks]
ii.
If this DNA molecule is transcribed, which strand will be the template
strand and which will be the non-template strand? [3 Marks]
iii.
Where, approximately, will the start site of transcription be? [3 Marks]
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B. A geneticist discovers that two different proteins are encoded by the same
gene. One protein has 56 amino acids and the other 82 amino acids. Provide a
possible explanation for how the same gene could encode both of these
proteins. [5 Marks]
C. A circular molecule of DNA contains 1 million base pairs. If DNA synthesis
at a replication fork occurs at a rate of 100,000 nucleotides per minute,
i. How long will theta replication require to completely replicate the molecule,
assuming that theta replication is bidirectional? [3 Marks]
ii. How long will replication of this circular chromosome take by rolling-circle
replication? [3 Marks]
4.
A. Compare the roles of general transcription factors and transcriptional activator
proteins. [3 Marks]
B.
i.
What makes up the spliceosome? [2 Marks]
ii.
What is the function of the spliceosome? [2 Marks]
C. Explain DNA methylation and state its importance in bacteria? [6 Marks]
D.
i.
What is difference between positive and negative control in gene
expression? [3 Marks]
ii.
What is the difference between inducible and repressible operons?
[4 Marks]
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