Question

RNA polymerase I catalyze
A. Elongation in transcription
B. rRNA synthesis
C. mRNA synthesis
D. tRNA synthesis

Answer 1

The transcription process is catalyzed by various RNA polymerases in eukaryotes, which are responsible for the formation of different types of RNAs, such as ribosomal RNA, micro-RNA, nuclear RNA, etc. RNA polymerase I catalyse RNA associated with ribosomes.

Complete answer:
RNA polymerase is an enzyme that synthesises RNA from a DNA template. The prokaryotic RNA polymerization initiates the transcription process and has a sigma factor which dissociates the enzyme following initiation factor for the process of transcription. The same RNA is used in prokaryotes to catalyze the coding and non-coding of RNA polymers. In eukaryotes, the polymerization of RNA is catalyzed by various RNAs. In eukaryotic cells, there are three types of nuclear RNA polymerases. The first type of RNA is called pre-ribosomal RNA, i.e. it synthesizes RNA polymerase 1 (Pol I or pre-rRNA). The synthesis of tRNAs and some other small specialized RNAs is performed by other RNA polymerases. In the elongation process, the enzyme adds ribonucleotides to the primer. Although DNA and RNA polymerases catalyze nucleotide polymerization reactions, their activity is different. They can also start the reaction from the centre of a DNA strand and read 'STOP' signals which distinguish the enzyme complex from the template.
Hence, the correct answer is option B.

Note: Eukaryotes have multiple forms of RNA polymerases that transcribe different genes. RNA polymerase I is involved in rRNA gene transcription, while RNA polymerase II is involved in mRNA, miRNA, and snRNA gene transcription. The transcription of tRNA and 5S rRNA genes is involved in RNA polymerase III.