Question

Describe how the bacterial lac operon works

What is the energy of activation?  Do endergonic reactions possess an energy of activation?  What about exergonic reactions

What is the function of NADH & FADH2 in cell respiration

How do proteins & fats get incorporated into the cell respiration pathway

In the fermentation pathway, why do we need to form lactic acid even though no ATP is formed during this step?

Answer 1

Ans- Lac operon

               An operon defines as a functioning unit of genomic DNA that consists of a group of genes which is controlled by a promoter. The lac operon is expressed in E. coli in two conditions when lactose is available, and glucose is not available.

The lac operon consists of three genes such as lacZ, lacY, and lacA and a promoter, a terminator, regulator, and an operator.

1. The lacZ encodes a β-galactosidase enzyme that breakdown the lactose into glucose and galactose.
2. The lacY encodes permease enzyme that increases the cell permeability to β-galactosides.
3. The lac A encodes transacetylase enzyme that helps in transferring an acetyl group from acetyl-CoA to β-galactosides.

     

Transcription starts when RNA polymerase binds to the promoter.CAP or cAMP-bound catabolite activator protein helps RNA polymerase binds to the promoter. The lacI gene is a regulatory gene that produces lac repressor protein that blocks the transcription process when binds to the operator. The repressor protein is removed when allolactose binds to it. The lac operon is switched off when a repressor binds the operator that preventing transcription.

In the presence of lactose, allolactose(inducer) that binds to the repressor protein. Therefore, the lac repressor is unable to bind the operator, so RNA polymerase can easily bind to the operator for the transcription of mRNA.