RNA processing

Question 1

how does modification of mRNA after transcription before translation differ in prokaryotes and eukaryotes?

Answer 1

prokaryotes: none
eukaryotes: additions to mRNA ends and intron removal

Question 2

what is the 5’ cap?

Answer 2

chemically modified molecule of GTP

Question 3

what is the function of the 5’ cap and when is it added?

Answer 3

• facilitates binding of mRNA to an enzyme (ribosome) for translation
• protects mRNA from being digested by ribonucleases
• added during transcription

Question 4

what is the 3’ tail?

Answer 4

poly A tail: 100-300 adenine nucleotides

Question 5

what is the function of the 3’ tail and when is it added?

Answer 5

• export of mRNA from nucleus to cytoplasm
• mRNA stability
• added immediately after mRNA transcript has been released from RNA polymerase

Question 6

what are introns?

Answer 6

non-coding sequences in genes

Question 7

what is intron removal called and what proteins perform it?

Answer 7

splicing - performed by small nuclear ribonucleoproteins (snRNPs), which form the spliceosome; bind by consensus sequence (complementary base pairing) to remove

Question 8

describe the process of RNA splicing

Answer 8

a) cut made between 5’ exon and intron -> intron forms a closed loop
b) free exon group a cut end of exon reacts w the 5’ phosphate of other exon
c) 3’ exon cleaved and spliced to 5’ exon: mature mRNA
d) excised intron us degraded into nucleus