5. Consider a colony of coli cells that have a mutation in the lac I gene, resul

Question

5. Consider a colony of coli cells that have a mutation in the lac I gene, resulting in a LacR protein that cannot bind to allolactose. Describe the effect that this mutation will have on the lac operon in terms of B-gal protein levels when the cells are grown in media containing lactose but no glucose. Explain your reasoning. (3 points) 6. Consider a colony of coli cells in which the gene for the CRP protein is deleted. Describe the effect of that this deletion will have on the arabinose operon in terms of Ara A protein levels when the cells are grown in media containing arabinose but no glucose. Explain your reasoning. (3 points) 7. Draw what the results for a Northern blot, probing for ara a mRNA, would look like for coli cells grown under the following conditions: 1) arabinose absent and glucose present, 2) arabinose present and glucose absent, 3) arabinose present and glucose present. Explain your reasoning. (4 points) 8. Draw what the results for an EMSA would look like for the following samples: 1) CRP CAMP+lac operon DNA sequence, 2) CRP lac operon DNA, 3) LacR allolactoselac operon DNA, 4) LacR lac operon DNA, 5) AraC + arabinose ara operon DNA sequence, 6) AraC ara operon DNA sequence. For you drawing, assume that the lac operon DNA sequence and ara operon DNA sequence are approximately the same size. CRP dimer weighs 84 kDa, LacR tetramer weighs 154 kDa, and the AraC dimer weighs 72 kDa. (3 points)

Explanation / Answer

5) A mutation in lac I such that the resulting lacR protein does not bind to allolactose has a great effect on lac operon. The mutation is known as Is and in that a repressor protein binds to the operator and it does not get off the operator even if the lactose is present in the medium. The mutation changed the conformation of the repressor that could bind to the allolactose and the operon is turned off regardless the lactose present in medium.

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