Question

Gene Regulation

Describe the regulation of the lac operon in E. coli.

a. the structure of lac operon in E.coli.

b. Role of CAP and cAMP the activator binding site

c. Role of Lac Repressor and Operator and Inducer

d. Role of Looping

e. Effect of mutations

f. Recessive v dominant mutations

g. Complementing v noncomplementing mutations.

Describe the regulation of the trp operon in E. coli.

Describe at least three kinds of molecular switches involved in gene regulation.

What is the signal in each case?

How many different components are there?

Are interactions positive or negative?

Describe at least three other ways of regulating gene expression in a cell.

Answer 1

1.The lac operon in E. coli contains three structural genes, in addition to regulatory genes. The structural genes include: lacZ – which encodes the enzyme, β-galactosidase; lacY – which encodes the enzyme, lactose permease; and lacA – which encodes the enzyme, lactose transacetylase.

2.CAP binds cAMP and in the process its conformation is altered so that it becomes a gene activator. The cAMP Cap complex binds to DNA at or near the promoter sites for susceptible genes. The ultimate effect of CAP binding to a promoter site is to stimulate the transcription of the promoter-associated genes.

3.The lac repressor is a protein that represses (inhibits) transcription of the lac operon. It does this by binding to the operator, which partially overlaps with the promoter. When bound, the lac repressor gets in RNA polymerase's way and keeps it from transcribing the operon.

4.The looping model has been proposed to allow for direct contact of promoters and enhancers over long distances. In this model, the enhancer and promoter make contact by looping out the intervening chromatin .