SBC 222 PAST PAPER

KENYATTA UNIVERSITY
UNIVERSITY EXAMINATIONS 2009/2010
FIRST SEMESTER EXAMINATION FOR THE DEGREE OF
BACHELOR OF SCIENCE IN BIOCHEMISTRY AND BIOTECHNOLOGY

SBC 222: NUCLEIC ACID AND PROTEIN METABOLISM

DATE:
Monday 28th December 2009
TIME: 11.00am – 1.00pm

INSTRUCTIONS: Section A: Answer any two questions (20 marks each)
1.
a)
Draw a diagram showing the reactions catalyzed by DNA polymerase that


occurs between deoxyribose at the end of the DNA chain and the 5’


phosphate of a deocyribonucleoside triphosphate. Include the chemical


structure of the phosphate group, indicate the location of sugar and base,


and show the rearrangement of electrons that occur.
[10marks]

b)
DNA synthesis on the lagging strand of E. Coli is a complex process


known to involve proteins. Initiation of a new chain is catalyzed by the


enzyme (i)_______________And elongation is catalyzed by the
enzyme
(ii)_____________Synthesis
is
discontinuous, yielding short
segments
called
(iii)________________,
which are eventually joined by


the enzyme (iv)_____________, which require the cofactor

(v)________________










[10marks]
2.
a)
Describe the sequence of events in the initiation of transcription by E. Coli


RNA polymerase.





[5marks]
Page 1 of 3

---

b)
The specific sequences that E. coli RNA polymerase binds to in E. coli


DNA before initiating transcription generally contain more A=T Base


pairs than G=C base pairs. In no more than a few sentences, speculate, on
why
this
might
be
the
case.
[5marks]

c)
Indicate whether each of the following statements is true (T) or False (F).
________________Eukaryotic
cells
have
three distinct RNA polymerases.


________________Eukaryotic mRNA are generally synthesized by RNA
polymerase
I


________________Eukaryotic RNA polymerase III synthesizes only
rRNAS.


_____________All tRNAS have the sequence---CCA at their 5’ terminus
____________Eukaryotic
RNA
polymerases
initiate transcription at


specific sites on the DNA (Promoters), but prokaryotic polymerases do


not.







[10marks]
3.
Using appropriate illustrations, describe DNA repair by the following systems.
a)
Base-excision
repair.
[10marks]
b)
Nucleotide
excision
repair.
[10marks]

SECTION B: Answer all questions (10 marks each)

4.
Indicate whether each of the following statements is true (T) or false (F).

i)
Assembly of a complete ribosome onto a MRNA requires GTP hydrolysis.

ii)
Animoacylation or “charging” of tRNA requires the formation of
aminoacyl-AMP
intermediate.

iii)
Aminoacyl-rRNA binding to the A site of the ribosome requires the


accessory factor EF-Tu and GTU hydrolysis.

iv)
Translocation of growing polypeptide from the A and P site on the


ribosome requires EF-G and GTP hydrolysis.

v)
Termination of translocation does not require the hydrolysis of any high
energy
phosphate
bonds.

Page 2 of 3

---

5.
Describe the formation of the initiation complex during protein synthesis in
bacteria.

6.
a)
List five processing reactions involved in posttranslational modifications.










[5marks]

b)
How do the following compounds inhibits protein synthesis?











[5marks]


i)
Puromycin
ii)
Tetracycline.