Short Quiz on RNA Polymerase (RNAP)
Instruction
2. There is 1 Mark for each correct Answer
(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:
- r RNA
- m RNA, mi RNA, Sn RNA
- 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.
The sigma (σ) subunit of prokaryotic RNA polymerase:
C i.e. Specifically recognizes the promoter site
The σ subunit (“sigma factor”) enables RNA polymerase to recognize promoter regions on the DNA.
RNA polymerase does not require :
D i.e. Primer
A specific RNA polymerase called primase (DnaG), synthesizes the short stretches of RNA (approximately ten nucleotides long) that are complementary and antiparallel to the DNA template.
In the resulting hybrid duplex, the U in RNA pairs with A in DNA.
These short RNA sequences are constantly being synthesized at the replication fork on the lagging strand, but only one RNA sequence at the origin of replication is required on the leading strand.
The substrates for this process are 5′-ribonucleoside triphosphates, and pyrophosphate is released as each ribonucleoside monophosphate is added through the formation of a 3’→5′ phosphodiester bond.
The drug inhibiting DNA-dependent RNA polymerase in Mycobacteria is –
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 of mycolic acid into bacterial cell wall by inhibiting arabinosyltransferase.
RNA polymerase has which activity
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.