Chapter 38 - RNA Processing

Question 1

rRNA

Answer 1

Ribosomal. Made by RNA polymerase I.

Question 2

tRNA

Answer 2

Transfer. Made by RNA polymerase III. Cloverleaf shape with anticodon for mRNA and acceptor stem for amino acid.

Question 3

RNA Polymerase I

Answer 3

Synthesizes a large precursor RNA (45S) that is subsequently processed to yield 18S, 28S, and 5.8S rRNAs, which are components of the ribosome. Prior to cleavage, the precursor is altered by modifications of some bases and riboses that are catalyzed by RNA-protein complexes called small nucleolar ribonucleoproteins (snoRNPs).

Question 4

RNase P

Answer 4

Removes nucleotides from the 5’ end.

Question 5

RNase Z

Answer 5

Removes nucleotides from the 3’ end.

Question 6

tRNA Nucleotidyltransferase

Answer 6

Adds nucleotides to the 3’ end.

Question 7

Endonuclease

Answer 7

Removes introns.

Question 8

Common Features In Intron-Exon Junctions

Answer 8

1) The 5’ end of the junction has the consensus sequence 5’ AGGUAAGU 3’ with the first GU from the 5’ end marking the beginning of the intron.
2) The 3’ end of the intron is marked by a stretch of pyrimidines (polyprimidine tract) followed by any base, a C, and then the intron ends with AG.
3) The branch site is located 20-50 nucleotides from the 3’ end of the intron.