RNA Polymerase (RNAP)

(40)        Promoter site REF: Harper 27`^h ed p. 349

RNA polymerase has sigma sub unit which recognises promotor nucleotide sequence. It does not require primer and has no proof reading activity

Types:

1. r RNA
2. m RNA, mi RNA, Sn RNA
3. t- RNA, 5s-rRNA, some SnRNA

DNA polymerase can only elongate existing polynucleotide chains, and thus requires a primer. RNA polymerase can initiate RNA synthesis de novo and hence does not require a primer.

Ref: Molecular Biology of the Gene Watson, 2004, Page 376 ;  Lippincott’s Illustrated Q & A Review of Biochemistry by Michael A. Lieberman, Rick Ricer, 2009, Page 294

C i.e. Specifically recognizes the promoter site

D i.e. Primer

Ans. is ‘b’ i.e., Rifampicin

Mechanism of action of important antitubercular drugs

o Rifampicin —> Inhibits DNA dependent RNA synthesis by inhibiting RNA polymerase.

o INH  —> Inhibits synthesis of mycolic acid which is a component of mycobacterial cell wall. o Pyrazinamide —> Inhibits synthesis of mycolic acid.

o Streptomycin —> Inhibits protein synthesis (translation).

o Ethambutol —> Inhibits incorporation ofmycolic acid into bacterial cell wall by inhibiting arbinosyltransferase.

 DNA synthesis cannot commence with deoxyribonucleotides because DNA polymerase cannot add a mononucleotide to another mononucleotide.

• Thus, DNA polymerase cannot initiate synthesis of complementary DNA synthesis strand of DNA on a totally single stranded template.
• For this, they require RNA primer, which is a short piece of RNA formed by enzyme primase (RNA polymerase) using DNA as a template.
• RNA primer is then extended by addition of deoxyribonucleotides.
• Later on, the ribonucleotides of the primer are replaced by deoxyribonucleotides.
• Primase is actually a DNA primase which has RNA polymerase activity. This DNA primase is also called DNA polymerase.