(a) Name the enzyme that catalyzes the transcription of hnRNA.

(b) Why does the hnRNA need to undergo changes? List the changes hnRNA undergoes and where in the cell such changes take place.

OR

(a) Explain DNA replication with a suitable diagram.

(b) Write the characteristics of the genetic code.

(c) What are the 3 types of RNA molecules and how they are related?

(a) RNA Polymerase II catalyzes the transcription of hnRNA.

(b) hnRNA contains both exons, the coding sequence and introns, the non-coding sequence. Introns are non-functional which is why they are removed by the process of splicing and exons are then joined together.

The post transcriptional modification of hnRNA takes place by 5' capping, 3' tailing and splicing.

OR

(a)

Figure showing DNA replication.

(b) Characteristic features of the genetic code are:
i. Universal: Same genetic code used by all living organisms
ii. Unambiguous: One amino acid (or start or stop) is coded by each codon.
iii. Degeneracy: Most of the amino acids are encoded by more than one codon.
iv. Triplet: Three nucleotides together forms one codon
v. There is one start codon(AUG) and three stop codons (UAA, UAG, UGA).

(c)


The figure shows the functions of 3 types of RNA.

mRNA, tRNA, and rRNA are related to the process of protein synthesis and gene expression.

mRNA is translated to form the protein.

tRNA carries the amino acid to the site of protein syntheis.

rRNA forms the structural component of ribosomes and ribosomes help in protein synthesis (translation).