NEET Botany Molecular Basis of Inheritance Questions Solved

BOARD

(a) Describe the process of transcriptionin bacteria.

(b) Explain the processing the hRNA needs to undergo before becoming functional mRNA in 

      eukaryotes.                                (5 marks)

(a) Process of transcription in bacteria :

  (i) Initiation - DNA dependent RNA polymerase associates with the initiation factor or stigma

       factor and binds to the promoter site of DNA. Thus initiates transcription.

 (ii) Elongation - One of the two strands of DNA functions as template. RNA polymerase helps in

      opening of helix and continuous elongation. The two strands of DNA uncoil progressively from

      the site of polymerase binding. RNA polymerase uses nucleotide triphosphate as a substrate

      and polymerises nucleotide in a template in 5' to 3' direction, following the rule of complemen-

      tarity.

 (ii) Termination - When the RNA polymerase reaches the terminator region, m-RNA gets sepera-

       ted from DNA. RNA polymerase associates with rho (ρ) and both the enzymes and the newly

       formed/nascent RNA fall off from the DNA.

                   

 

(b) 

 1. The structural genes are monocistronic in eukaryotes. The process of transcription is similar to

     that in prokaryotes. It takes place in the nucleus.

 2. The hnRNA undergoes two additional processes called capping and tailing.

 3. In capping, methyl guanosine triphosphate is added to the 5' end of hnRNA.

 4. In tailing, adenylate residues (about 200-300) are added at 3' end.

 5. Now the hnRNA undergoes a process where the introns are removed and exons are joined to

      form mRNA by the process called splicing.

In Eukaryotes, three types of RNA polymerases are found in the nucleus. These are :

 (i) RNA polymerase I transcribes rRNAs (28S, 18S, 5.8S)

 (ii) RNA polymerase II transcribes the precursor of mRNA called heterogenous nuclear RNA or

      hnRNA.

(iii) RNA polymerase III transcribes tRNA, 5srRNA and SnRNAs (small nuclear RNAs).

         

                                                           Messenger RNA (mRNA)  

Difficulty Level:

  • 89%
  • 6%
  • 6%
  • 0%