(a) Explain and illustrate the steps involved to make fully processed hnRNA?

Question

Observe the segment of mRNA given below.

(a) Explain and illustrate the steps involved to make fully processed hnRNA?

(b) Gene encoding RNA Polymerase I and III have been affected by mutation in a cell. Explain its impact on the synthesis of polypeptide, stating reasons.

OR

Study the schematic representation of the genes involved in the lac operon given below and answer the questions that follow:

(a) The active site of enzyme permease present in the cell membrane of a bacterium has been blocked by an inhibitor, how will it affect the lac operon?

(b) The protein produced by the i gene has become abnormal due to unknown reasons. Explain its impact on lactose metabolism stating the reason.

(c) If the nutrient medium for the bacteria contains only galactose; will operon be expressed? Justify your answer.

Answer 1

(a) The hnRNA undergoes processes called capping and tailing followed by splicing .In capping, an unusual nucleotide is added to the 5¢-end of hnRNA methyl guanosine triphosphate.In tailing, adenylate residues (about 200–300) are added at 3¢-end in a template independent manner. Now the hnRNA undergoes a process where the introns are removed and exons are joined to form mRNA called splicing.

(b) The process of translation will not happen, thus the polypeptide synthesis is stopped/ hampered.

The reason for the above is: RNA polymerase I transcribes rRNAs which is the cellular factory for protein synthesis.

RNA polymerase III helps in transcription of tRNA which is the adaptor molecule/ that transfers amino acids to the site of protein synthesis.

OR

(a) When the active site of enzyme permease present in the cell membrane of a bacterium has been blocked by an inhibitor, the lactose is not transported into the cell. As lactose is the inducer, the lac operon will not be switched on.

(b) Since the repressor protein synthesized by the i gene is abnormal, it will not bind to the operator region of the operon, resulting in a continuous state of transcription process

(c) No, because galactose is not an inducer/ it is a product of lactose metabolism