What is the role of lactose in regulating lac operon expression?

Answer 1

When the lac operon controls the expression of proteins in the E.coli cell that can break down lactose into two sugars, glucose and galactose.

When lactose is present, it binds to the repressor that typically sits on the lac operon, changing the repressor's conformation such that it can no longer bind to the lac operon. Because of this, RNA polymerase can now transcribe the gene into mRNA, which in turn is translated into the proteins that can break down lactose.

Answer 2

Operons in general are made up of the following:

1. A promoter (A segment of DNA usually occurring upstream from a gene which acts as a controlling element in the expression of that gene)

2. Two or more structural Genes (genes which code for protein or RNA which are specifically NOT involved in regulatory functions)

3. An Operator (short sequence of DNA between promoter and structural genes which controls the transcription of the operon itself)

The Lac Operon is a specific operon which is induced by the presence of the sugar lactose in the cell, specifically E. Coli. In the bacterial vector (the bacterial genome), a repressor is found on the promoter region of the DNA in the absence of lactose. When lactose is present in the system surrounding E. Coli, the lactose diffuses across the cell membrane. These molecules of lactose interact with the repressor molecule and cause it to unfasten its grasp from the bacterial vector, allowing RNA polymerase to transcribe the genes which were otherwise inhibited. As dictated by the central dogma of Biology, these genes then turn into proteins through translation. One of the new proteins formed allow for faster lactose diffusion and the other converts lactose into glucose, a more usable form of energy for the cell.

Answer 3

The lac I gene encodes a repressor. Allolactose (i.e. the inducer) is derived from lactose in a reaction which is catalysed by beta-galactosidase. If the inducer is absent, the repressor binds to the lac operator. This represses the transcription of structural genes. However, if the inducer is present, the repressor will bind it it instead. The repressor will be released from the operator and the transcription of the structural genes is turned on.

Answer 4

it is regulated by the lac genes in E. coli which are turned off by repressors and turned on by he presence of lactose.

Answer 5

Lac R, is the coding region that produces the regulator. The lac operon is under negative inducible control in the presence of lactose

Answer 6

it is a sugar found in milk and it synthesizes those enzymes that are necessary to take up lactose and use it as energy.

Answer 7

It induces transcription by binding to the repressor and removing it from the operator.

Answer 8

The presence and absence of lactose.

Answer 9

The repressor gene.