Q. 26

(a) Describe amin

Answer :

a) Enzyme Amino acyl tRNA synthesases catalyses aminoacylation of tRNA by joining the amino acid to its cognate tRNA.The selection of cognate is done by structural domains that examine different regions of the tRNA.

b) When mRNA makes its entry into it in a prokaryote, this mRNA reaches the ribosomes.Now, the ribosome uses the information inside the mRNA to build a protein which has a specific amino acid sequence.


1. The Operon model was given by François Jacob and Jacques Monad in 1961.

2. Operon is a cluster of genes which have related functions and are involved in the catabolism or degradation of lactose.

3. There are two types of operons, Inducer operon also called Lac Operon (lactose) and Trp Operon also called Repressor operon (Tryptophan operon).

Inducible Operator System:

1. It is an operon also known as Lac Operon found in bacteria E. coli.

2. When E. coli feeds on something it prefers Glucose over lactose.

3. When Glucose is fully taken up by the E. coli, it starts using Lactose.

4. When intake of lactose is started by E. coli, Lac operon gets activated which proves that lactose is an inducer for the Lac Operon.

Structure of Lac Operon:

Working of Lac Operon:

1. In the operon gene ‘i’ undergoes transcription and forms a messenger RNA or m-RNA.

2. This m-RNA undergoes translation to form repressor protein.

3. Now the repressor protein combines together to form repressor tetramer.

4. The promoter site or gene ‘p’ is the binding site for enzyme RNA polymerase.

5. As the repressor tetramer moves towards the operator site to bind to it, lactose present in the E. coli breaks down the tetramer.

6. Due to which the operator gets unblocked and makes it able for enzyme RNA polymerase to move forward from the promoter site.

7. This enables the enzyme RNA polymerase to start transcribing structural gene z,y and a.

8. Gene ‘z’ coding for enzyme p-galactosidase breaks down into glucose and lactose.

9. Gene ‘y’ coding for enzyme permease provides the entry of more lactose in the bacteria E.coli.

10. Gene ‘a’ coding for transacetylase adds the acetyl group to beta galactosidase to activate beta galactosidase.

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