Question:

In E.coli, the lac operon gets switched on when

Updated On: Sep 14, 2022

lactose is present and it binds to the repressor
repressor binds to operator
RNA polymerase binds to the operator
lactose is present and it binds to RNA polymerase

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The Correct Option is A

Solution and Explanation

A lac operon is made up of regulatory DNA sequences and three genes that encodes different products. Regulatory proteins bind to the DNA sequences controlling the transcription. The three DNA sequence regions in a lac operon are:

Promoter
Operator
CAP Binding Site

When lactose is absent, a repressor protein binds to the operator region preventing transcription and thus keeping the operon off. However, when lactose is present, it binds to the repressor protein altering its shape and thus dissociating it from the operator. Once the repressor is released, RNA polymerase can bind and carry out transcription of genes. Thus, lactose is needed to turn on the lac operon.

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Notes on the molecular basis of inheritance

Concepts Used:

The Molecular Basis of Inheritance

DNA Replication:

DNA synthesis is commenced at particular points within the DNA strand referred to as ‘origins’, which are certain coding regions. There are numerous origin sites, and when replication of DNA starts, these sites are mentioned as replication forks. Within the replication, the complex is the enzyme DNA Helicase, so that they can be utilized as a template for replication. DNA Primase is another enzyme that's essential in DNA replication.

RNA:

Ribonucleic acid (RNA) is an essential biological macromolecule that exists all together in biological cells. It is principally involved in the synthesis of proteins, that carry the messenger instructions from DNA, which itself contains the genetic instructions needed for the event and maintenance of life. In some viruses, RNA, in spite of DNA, carries genetic information.

Genetic Code:

Genetic code is the term we use in the manner that the four bases of DNA--the A, C, G, and Ts--are strung together in a way that the ribosome, the cellular machinery, can read them and switch them into a protein. In the ordering, every three nucleotides during a row count as a triplet and code for one amino alkanoic acid.

Read More: Molecular Basis of Inheritance