Question

below is the mutated lactose (lac) operon in a partial diploid.

I+ P+ Oc Z? Y+ / I- P+ O+ Z+ Y?

Predict the expression of the lac genes in the presence of lactose and Explain your answer by drawing a diagram how the presence of lactose acts to either induceor repress the expression of the lac genes

Answer 1

Answer:

The operon is a cluster of genes. It contains both structural and regulatory genes. Lac operon is present in E.Coli. E.coli required the glucose is as C source. If lactose is present as C source, cannot be utilized directly. So E.Coli activates the Lac Operon. This Activated Lac operon gene produces the enzymes from structural genes which convert the lactose into glucose and galactose. This glucose utilized as a C source.

Lac operon consists, three regulatory genes/ sequences and three structural genes.

Regulatory genes:

Lac i: This gene code for a regulatory protein which is repressor molecule. This bind to the operator and prevent the entry of RNA pol into structural genes.

Lac p: Is promoter region on DNA. To which RNA pol will bind.

Lac O: Is sequence present on DNA, to which repressor will bind.

Structural Genes:

Lac Z: Code for beta-galactosidase. This enzyme can split the lactose into glucose and galactose. Also involved in the isomerization of lactose into allolactose.

Lac Y: Produces the enzyme permease. Acts as a carrier molecule and allowing entry of lactose into the cell.

Lac a: Code for enzyme galactoside transacetylase. The function is not clear. May help in removal of toxic substances.

In general, If lactose is present:

Lac i produce the active repressor which goes and binds to the operator and prevents the entry of RNA pol into structural genes. In this case, a small amount of lactose isomerized into allo-lactose. This allolactose acts as an inducer. It goes and binds to repressor at operator site and removes the repressor. So free operator is allows the entry of RNA pol into structural genes. These enzymes from structural genes convert lactose into glucose and galactose. This Glucose utilized by cells.

In general, If lactose is absent:

Lac i produce the active repressor which goes and binds to the operator and prevents the entry of RNA pol into structural genes. In this case, lactose not form allolactose. So active repressor bind to operator which restrict the entry of RNA pol into structural genes. So Lac operon is inactive.

I+ P+ Oc Z? Y+ / I- P+ O+ Z+ Y?

Each gene having two alleles. Here I+/I- means one allele able to produce active repressor but another one not. Over all active repressor is available in this condition. This repressor can bind to operator.

P+/P+ means promoter is functional. RNA pol can bind to promoter.

Oc/O+ means one allele of operator get mutated which will not allow RNA pol to enter into structural genes. But another loci of O+ can allow RNA pol to enter into structural genes.

Z-/Z+ B-galactosidase can produced by one allele, another allele mutated and not produce enzyme. But over all B-galactosidase produced.

Y+/Y- permease can produced by one allele, another allele mutated and not produce enzyme. But over all permease produced.

From this explanation, Lac operon can perform normally. When Lactose is present operon is in active condition. When lactose is absent, the operon is in inactive condition.

If Lactose is present: operon is in active condition

If lactose is absent, Lac operon is inactive.