Question

6.       Compare the structure and function of a typical DNA polymerase and a typical RNA polymerase.

7.       What are the post-transcriptional modifications that the pre-mRNA is subjected to in eukaryotes? Explain by giving the role(s) of each modification.

8.       Highlight the general characteristics of a mature mRNA in comparison with rRNA or tRNA

Answer 1

6.

• DNA polymerase is an enzyme used to synthesise DNA molecule from a process called DNA replication. Whereas, RNA is used for the synthesis of mRNA from DNA and the process is referred as transcription.
• DNA is used or active during the S phase of the interphase whereas the RNA is used during the G1 and G2 of the growth phase.
• For the replication of the DNA by DNA polymerase it requires a primer for binding. RNA polymerase does not require any polymerase.
• RNA has no proofreading systems unlike DNA.
• RNA polymerase is about 10 times slower than the DNA polymerase.
• RNA polymerase can make its own stand but the DNA.
• Both DNA and RNA follow 5'-3' synthesis direction.

7. Primary RNA which is going to be formed as mRNA after the translation process is called as pre-RNA. Transcription produced these pre RNA which is later produced into mRNA after translation process. During this process, it undergoes various modification which includes:

• 5' capping: while the pre-mRNA is still being synthesised, 7-methylguanosine cap is added to the 5' end by a phosphate linkage to the growing side. This protects the nascent RNA from degradation by itself.
• 3' poly A tail: the pre mRNA is cleaved in a specific position by endonuclease and about 200 residue A tail is added which is referedd as the poly A tail.
• Splicing: For the production of mRNA introns need to be spliced out of pre mRNA only them can the mRNA start to encode. The process of removing the introns and connecting the exons is called as splicing which has to be accurate. If this fails, then the RNA will be dysfunctional.

8.  Mature messenger RNA is a eukaryotic RNA transcript that has been spliced and processed and is ready for translation in the course of protein synthesis.