The removal of introns from primary transcripts in eukaryotes is a carefully reg
ID: 72053 • Letter: T
Question
The removal of introns from primary transcripts in eukaryotes is a carefully regulated process, often restoring reading frames that had been disrupted by the introns.
a. Are introns removed from DNA molecule?
b. Are introns transcribed? translated? please explain
c. How are the beginnings and endings of introns and exons recognized by the enzymes of the splicosomes?
2. The following amino acid sequence is found in a tripeptide: Met Trp His. Give all the possible nucleotide sequences on the mRNA and the template strand of the DNA that can encode this tripeptide.
I would like to know if I'm on the right track, I did the questions, but not sure if I'm right.
Explanation / Answer
a. Introns are not removed from DNA molecule.
b. Introns are transcribed but not translated. RNA splicing takes place during the RNA processing of the final RNA product as a result of which introns are removed from the RNA. This process is followed by transcription and preceded by translation.
c. Within the intron, a donor site (5' end of the intron), a branch site (near the 3' end of the intron) and an acceptor site (3' end of the intron) are required for splicing.The splice donor site includes an almost invariant sequence GU at the 5' end of the intron, within a larger, less highly conserved region. The splice acceptor site at the 3' end of the intron terminates the intron with an almost invariant AG sequence. Upstream (5'-ward) from the AG there is a region high in pyrimidines (C and U), or polypyrimidine tract. Upstream from the polypyrimidine tract is the branchpoint, which includes an adenine nucleotide.
The spliceosome consists of U1, U2, U4, U5 and U6 snRNPs, U2AF1, U2AF2, and SF1. The spliceosome forms different complexes and recognizes the particular sequence near the 3' end of the introna which is covalently attached to the 5' end and forms a branched intron during splicing.
2. Met Trp His
mRNA ----> DNA
AUG UGG CAC ----> ATG TGG CAC
AUG UGG CAU ----> ATG TGG CAT