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Posted By: amit Member Level: Gold Posted Date: 27 Jun 2008
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2007 Birla Institute of Technology-Mesra B.E MOLECULAR MECHANISM OF GENE EXPRESSION University Question paper
BIRLA INSTITUTE OF TECHNOLOGY & SCIENCE, PILANI
I SEMESTER 2007-08
BIO G512
MOLECULAR MECHANISM OF GENE EXPRESSION
COMPREHENSSIVE EXAMINATION
Duration: 3.0 HRS 13.12.2007 w’tage;40%
1. Several eukaryotes are known in which a single effector molecule regulates the synthesis of different proteins coded by distinct mRNA molecules X and Y. At what level in process of gene expression does regulation occur in each of the following situations:
(a) Neither nuclear nor cytoplasmic RNA can be found for either X or Y.
(b) Nuclear but not cytoplasmic RNA can be found for both X and Y.
(c) Both nuclear and cytoplasmic RNA can be found for both X and Y but none of it is associated with polysomes. [1.5 +1.5 +2.0]
2 (a) Among mammals, the reticulocyte cells in bone marrow extrude their nuclei in the process
of differentiation into red blood cells. Yet the reticulocyte and red blood cells continue to synthesize haemoglobin. Suggest a mechanism by which haemoglobin synthesis can continue for a long time in the absence of the haemoglobin genes.
(b) A nonsense suppressor is isolated and shown to involve a tyrosine transfer RNA. When this
mutant t-RNAb is sequenced, the anticodon turns out to be normal, but a mutation is found in dihydrouridine loop. What does this finding suggest about how a t-RNA interact with m-RNA?
[2.5 marks each]
3. A mutant strain of E. coli is found that produces both ß-galactosidase and permease constitutively.
(a) What is/are the possible genotype(s) for this mutant?
(b) A second mutant is isolated that produces no active ß-galactosidase at any time but produces permease if lactose is present in the medium. What is the genotype of this mutant?
(c) A partial diploid is created from the mutant in (a) and (b). When lactose is absent, neither of the enzymes is made, and when lactose is present both enzymes are made. What is the genotype of the mutant in (a)? [2.5 marks each]
4. Tyrosine aminotransferase (TAT) activity in liver cells grown in culture increases when the cells are exposed to steroid hormones. Assume this activity is genetically regulated in a manner analogous to lac operon control in E. coli.
(a) Describe the phenotype of liver cell mutants altered in the structural genes.
(b) Describe the phenotype of a liver cell mutant that was obviousely altered in a regulatory gene for TAT enzyme.
(c) How could you tell whether a mutation in this system was dominant or recessive?
[2.5 marks each]
P.T.O.
5. (a) If you want to redesign mouse genome to increase antibody diversity, but by adding the
least amount of DNA, which component would you increase?
(b) If an organism has 150 different V- genes, 12 J-genes, and 3 possible V-J joints for L chains,
and can make 5000 different H chains, how many different antibodies can be made?
[2.5 marks each]
6. (a) An E. coli cell containing F can transfer the chromosome at a frequency of about one
transfer event per cell. Is this donation o conduction? And does it occur in a recombination-deficient cell? Can colE1 cause chromosome transfer
(b)It has been stated that helicases are needed because no DNA polymerase can unwind a double helix. However, before helicases were discovered, enzymologists were able to replicate DNA using reaction mixtures that probably contained no helicases. What property of DNA allows advance of the replication fork without a helicase? What effect would you expect a helicase to have on either the rate or fidelity of replication? [2.5 marks each]
7. (a)What are the fundamental differences between the centromeric nucleosome and the conventional nucleosome? Explain
(b) Is this important to investigate the role of chromosome territories, and factors that organize these territories, in recombination and genome instability? Explain. [2.5 marks each]
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