The pace at which light passes through objects in phase contrast microscopy is-

#Question id: 2855

#Unit 2. Cellular Organization

Which statements are correct about lac operator;

I. The site bound by the Lac repressor.

II. The lac operator overlaps the promoter, and so the repressor bound to the operator physically prevents RNA polymerase from binding to the promoter and thus inhibit the RNA synthesis.

III. Have 21-bp sequence with twofold symmetric and is recognized by four subunits of Lac repressor, two binding to each half-site.

IV. CAP binds as a dimer to a site similar in length to that of the lac operator, but different in sequence. This site is located some 60 bp upstream of the start site of transcription.

#Question id: 2856

#Unit 2. Cellular Organization

Match the lac genes with their enzymes & functions;

#Question id: 2857

#Unit 2. Cellular Organization

In one experiment, another protein –protein interaction is used in place of that between CAP and polymerase. This is done by taking two proteins known to interact with each other, attaching one to a DNA-binding domain, and, with the other, replacing the carboxy-terminal domain of the polymerase a subunit (aCTD), which one is appropriate result of this experiment-

I. The modified polymerase can be inhibited if the appropriate DNA-binding site is introduced near the promoter.

II. The modified polymerase can be activated by the makeshift “activator” as long as the appropriate DNA-binding site is introduced near the promoter.

III. The activator having only to help polymerase bind to the promoter

#Question id: 2858

#Unit 2. Cellular Organization

When lactose enters the cell, it is converted to allolactose. It is allolactose (rather than lactose itself) that controls the Lac repressor. Paradoxically, the conversion of lactose to allolactose is catalyzed by b-galactosidase, itself encoded by one of the lac genes. How is this possible? Which statement is incorrect according lac genes expressions?

#Question id: 2859

#Unit 2. Cellular Organization

NtrC controls expression of genes involved in nitrogen metabolism by inducing a conformational change in a pre-bound RNA polymerase, triggering transition to the open complex.

I. Under low nitrogen level condition, NtrC is phosphorylated by a kinase, NtrB,

II. NtrC (bound to its sites upstream) interacts directly with s54. This requires that the DNA between the activator binding sites and the promoter form a loop to accommodate the interaction

III. Active NtrC binds four sites located approximately 150 bp upstream of the glnA gene.

IV. NtrC itself has an ATPase activity which provides the energy needed to induce a conformational change in polymerase.

Correct series of Activation by NtrC is;

#Question id: 2860

#Unit 2. Cellular Organization

 Lactose metabolism in E. coli is carried out by two enzymes, with possible involvement by a third. The genes for all three enzymes are clustered together and transcribed together from one promoter, yielding a polycistronic message. These three genes, linked in function, are therefore also linked in expression. They are turned off and on together.