Advertisements
Advertisements
Question
In E.coli, three enzymes β- galactosidase, permease and transacetylase are produced in the presence of lactose. Explain why the enzymes are not synthesized in the absence of lactose.
Solution
In the absence of lactose, the repressor protein binds to the operator and prevents the transcription of structural gene by RNA polymerase, hence the enzymes are not produced. However, there will always be a minimal level of lac operon expression even in absence of lactose.
RELATED QUESTIONS
When lactose is present in the culture medium:
Distinguish between structural gene, regulatory gene and operator gene.
A low level of expression of lac operon occurs at all the time. Justify the statement.
______ refers to the phenomenon by which a set of genes are switched on when there is necessity to metabolise a new substrate.
Identify the process described in the following paragraph.
Repressible regulation of gene is seen when the end product of a biosyntbetic pathway like amino acid, is provided in the medium. At this time, internal biosynthesis of amino acid stops. It is negative control so the metabolite (amino acid) turns off a set of genes involved in producing that metabolite.
Which of the following factors regulate gene expression?
Which of the following is not a level at which gene expression can be regulated in eukaryotes?
Which of the following statements is correct about the role of regulatory proteins in transcription in prokaryotes?
Sometimes cattle or even human beings give birth to their young ones that are having extremely different sets of organs like limbs/position of eye(s) etc. Comment.
The gene which codes for enzyme β-galactosidase ______.
The image below shows the result of plating bacteria in a chromogenic medium after incorporating the gene of interest in the plasmid. Some plates had blue colonies; some plates had white colonies. A single bacterium extracted from Plate I, II, and III is shown below:
On the basis of your observations:
- Identify the plate(s) which is/are white. Give a reason.
- Identify the plate(s) which is/are blue. Give a reason.
Name the enzyme that catalyses the synthesis of the primary transcript.
List the changes that the primary transcript undergoes to become functional mRNA.
