Question

The Basics of Eukaryotic Gene Expression (Ch. 17)

• What are the steps of RNA processing? What are introns and exons? G-caps and PolyA tails?

• Does RNA polymerase function the same in eukaryotes as in prokaryotes? Why or why not?

• How do eukaryotic ribosomes compare with those of prokaryotes? How have these differences been used in

medicine?

• What is the evolutionary significance of the exon/intron arrangement in eukaryotic genes? What are domains?

Answer 1

Ans- RNA processing is the conversion of precursor m-RNA into mature m-RNA that occurs before translation. The process comprises of three steps-:

a) Addition of a 5' cap

b) Addition of a 3' Polyadenylation tail ( Poly- A tail)

c) RNA splicing.

Introns are the non-coding regions in m-RNA whereas exons are the coding regions in m-RNA. During the process of RNA splicing, introns are removed and exons are joined together to form a coding sequence.

A poly-A tail is a stretch of RNA that hasonly adenine bases. It is added to an RNA at the end of transcription.

G-cap is also known as 5' cap.It is an altered nucleotide at the 5' end ofsome primary transcripts which includes mitochondrial m- RNA, chloroplastic m-RNA and messenger- RNA.

Ans- The function of RNA polymerase is different in prokaryotes and eukaryotes. RNA polymerase is an enzyme that synthesizes RNA from a DNA template. Prokaryotes have only a single RNA polymerase to catalyze the formation of coding as well as non-coding strands. Whereas, eukaryotes have 5 distinct polymerases which are responsible for carrying out different functions ( synthesis of distinct subsets of RNA).