Topic 2 Molecular Genetics: mRNA Processing

Question 1

• Before leaving the nucleus, pre-mRNA undergoes several modifications:

Answer 1

Note

Question 2

• This sequence is added to the 5’ end of the mRNA; a guanine with 2 phosphate groups (GTP) provides stability for mRNA and a point of attachment for ribosomes

Answer 2

1. 5’ cap (5’ G-P-P-P-)

Question 3

• This sequence is attached to the 3’ end of the mRNA
• The poly A tail consists of 200 A nucleotides that serve to provide stability and control the movement of mRNA across the nuclear envelope
• In prokaryotes, the poly A tail actually facilitates degradation!

Answer 3

2. A poly-A tail (-A-A-A…A-A-3’)

Question 4

• Removes nucleotide segments from mRNA before mRNA moves into the cytoplasm via small nuclear ribonucleoproteins (snRNP’s). The spliceosome deletes the introns and splices the exons. Prokaryotes have no introns

Answer 4

3. RNA Splicing

Question 5

• Allows different mRNA to be generated from the same RNA transcript by selectively removing differences of an RNA transcript into different combinations

Answer 5

4. Alternative Splicing

Question 6

• It is important to learn that prokaryotes generally have ready to go mRNA upon transcription. Only eukaryotes undergo the processing mentioned in this section. Because prokaryotes don’t need to process their mRNA first, translation can begin immediately and simultaneously. In both prokaryotes and eukaryotes, however, multiple RNA polymerases can transcribe the same template simultaneously

Answer 6

Note