A low level of expression of lac operon occurs at all the time. Can you explain the logic behind this phenomena.

The repressor of the lac operon is synthesised all the time constitutively from the

Assertion :- Lactose is the substrate for the enzyme beta -galactosidse & it regulates switching on & off of the operon. Reson: A very low level of expression of lac operon is always present in cell all the time.

Go though the following statements (i) Meselson & stahl used cesium chloride density gradient to distinguish heavy DNA molecules from the normal DNA molecules. (ii) In meselson & Stahl experiment the DNA that was extracted from the culture one generation after the transfer from .^(15)N to .^(14)N , was composed of equal amount of hybrid (intermediate) DNA and of light DNA. (iii) In prokaryotes, control f the rate of transcriptional initiation is the predominant site for control of gene expression. (iv) In lac operon, the repressor is synthesised only at the time when the level of metabolite is in excess. Find out the correct statements?

(a) Absence of lactose in the culture medium affects the expression of a lac-operon in E.coli. Why and how ? Explain. (b) Write any two ways in which the gene expression is regulated in eukaryotes.

One physics expert has said that 'We cannot move our fingers without disturbing all stars'. Explain the logic behind this statement.

Suppose you are standing on a boat in the middle of a swimming pool. The boat is loaded with a bag of stones. Can you get to the shore using the stones ? If yes, explain the concept behind it.

In eukaryotes, regulation of gene expression can be done at all the following levels, except