Question

How many types of RNA polymerases are operative in eukaryotes?
A. Four
B. Three
C. Two
D. One

Answer 1

RNA Polymerase, ribonucleic acid polymerase is an enzyme that catalyzes the process of transcription. Transcription is synthesis of RNA polymer from DNA template. RNAP uses helicase to open up double stranded DNA and various other enzymes are used.

Complete answer:
Ribonucleic acid polymerase in an enzyme that catalyzes the process of transcription. It was discovered by Samuel B. Weiss and Hurwitz in 1960. The RNA polymerases generate RNA transcripts from genes encoded in the genome. Eukaryotes have RNAP which is highly similar to that of bacteria.
Transcription begins with the RNAP enzyme binding to specific sites of DNA, which is also called promoter region. The binding requires the presence of a few proteins in eukaryotes. A certain set of proteins called general transcription factors are crucial for transcription in eukaryotes along with transcription factors. Enzyme helicase is used by RNAP to open the double stranded DNA. Following this polymerase moves toward the promoter and loses most of its initiation factors. DNA strand unwinds to form a bubble where transcription occurs. On completion of transcription, RNA is processed.
Eukaryotes have three distinct RNA polymerases which transcribe different genes. The three types RNA polymerase are:
RNA polymerase I- transcribes rRNA genes
RNA polymerase II- transcribes mRNA, miRNA, snRNA, snoRNA
RNA polymerase III- transcribes tRNA, 5sRNA

Therefore, the correct answer to this question is option ‘B’- Three.

Note: Just like RNAPs, there are deoxyribonucleic polymerases, too. They are required in DNA replication. There is quite a difference between RNAPs and DNAPs, the latter requires primer to begin the polymerization reaction whereas RNAPs do not require any primers. RNAPs are slower than DNAPs.