Question

Question 22 Short Answer Question 1. Using each of the categories listed below, compare a typical fully mature eukaryotic mRNA with a typical prokaryotic mRNA. Describe the specific similarities and/or differences. Where possible, indicate the number and/or names of these regions. a. Non-coding region(s) (2 marks) b. Coding region(s) (2 marks) Shine-Dalgarno sequence(s) (2 marks) d. 5'modifications (2 marks) e. 3' modifications (2 marks) f. Does the mRNA require the formation of a loop before translation? (2 marks)

Answer 1

Answers

a) Introns are non-coding sections of a gene, transcribed into the precursor mRNA sequence, but ultimately removed by RNA splicing during the processing to mature messenger RNA. Many introns appear to be mobile genetic elements. In eukaryotes, noncoding regions called introns are often removed from newly synthesized mRNA. Introns are absend in prokaryotes.

b) Coding regions are composed of codons, which are decoded and translated into proteins by the ribosome. In eukaryotes usually into one and in prokaryotes usually into one and in prokaryotes usually into several. Coding regions begin with the start codon and end with a stop codon.

c) Eukaryotic mRNA does not have a Shine-Dalgarno sequence. Instead, eukaryotic ribosomes recognize the 5  cap structure, and the Kozak sequence, which is a loosely conserved sequence found around the first AUG. Prokaryotic mRNA is polycistronic and contains a Shine-Dalgarno sequence for ribosome binding. Eukaryotic mRNA are more complex and generally contain a cap and poly (A) tail.

d) In eukaryotes, the 5 end of the mRNA is protected from 5 to 3 exonucleolytic activity by the presence of the 5 cap structure. In prokaryotes, the 5 end of the newly transcribed mRNA is not further modified and ratains the 5 triphosphate.

e) The pre-mRNA molecule undergoes three main modifications. These modifications are 5 capping, 3 polyadenylation, and RNA splicing, which occur in the cell nucleus before the RNA is translated.

f) No, the hairpin loop forms in an mRNA strand during transcripton and cause the RNA polymerase to become dissociated from the DNA template strand. mRNA binding factors can also promote loop formation or cyclization, bringing the initiation and termination sites into close proximity.