Anonymous
06-04-2004, 10:02 PM
Problem 1: Post transcriptional modification to the 3'-end of eukaryotic mRNAs
What is added to the 3'-end of many eukaryotic mRNAs after transcription?
A. introns
B. a poly A tail
C. a cap structure, consisting of a modified G nucleotide
D. the trinucleotide 5'-CCA
E. exons
Transcription of eukaryotic protein-coding genes
Transcription of eukaryotic protein-coding genes results in an mRNA precursor molecule that is extensively processed in the cell nucleus.
When eukaryotic nuclear genes for proteins are transcribed by RNA polymerase, the product is a precursor RNA (pre-mRNA) that is further processed in the nucleus before transport to the cytoplasm for translation. The important processing steps are the following:
1. Capping. A modified G-nucleotide, termed a "cap", is added to the 5'-end of most mRNA. The cap is retained in mRNA, and functions in ribosome binding and mRNA stability.
2. 3'-Polyadenylation. A tail of A-nucleotides, generally 100-200 long, is added to the 3'-end of most eukaryotic pre-mRNAs. The poly A tail, which is not coded in the DNA, is also retained in the mRNA exported to the cytoplasm.
3. Intron Splicing. The pre-mRNA transcripts often contain introns, which are non-coding sequences that interrupt the coding regions known as exons. Introns are removed and exons are joined together by the spliceosome in the nucleus.
http://www.biology.arizona.edu/molecular_bio/problem_sets/mol_genetics_of_eukaryotes/graphics/01t.gif
ans:
B. a poly A tail
A tail of A-nucleotides, generally 100-200 long, is added to the 3'-end of most eukaryotic pre-mRNAs. The poly A tail, which is not coded in the DNA, is also retained in the mRNA exported to the cytoplasm.
What is added to the 3'-end of many eukaryotic mRNAs after transcription?
A. introns
B. a poly A tail
C. a cap structure, consisting of a modified G nucleotide
D. the trinucleotide 5'-CCA
E. exons
Transcription of eukaryotic protein-coding genes
Transcription of eukaryotic protein-coding genes results in an mRNA precursor molecule that is extensively processed in the cell nucleus.
When eukaryotic nuclear genes for proteins are transcribed by RNA polymerase, the product is a precursor RNA (pre-mRNA) that is further processed in the nucleus before transport to the cytoplasm for translation. The important processing steps are the following:
1. Capping. A modified G-nucleotide, termed a "cap", is added to the 5'-end of most mRNA. The cap is retained in mRNA, and functions in ribosome binding and mRNA stability.
2. 3'-Polyadenylation. A tail of A-nucleotides, generally 100-200 long, is added to the 3'-end of most eukaryotic pre-mRNAs. The poly A tail, which is not coded in the DNA, is also retained in the mRNA exported to the cytoplasm.
3. Intron Splicing. The pre-mRNA transcripts often contain introns, which are non-coding sequences that interrupt the coding regions known as exons. Introns are removed and exons are joined together by the spliceosome in the nucleus.
http://www.biology.arizona.edu/molecular_bio/problem_sets/mol_genetics_of_eukaryotes/graphics/01t.gif
ans:
B. a poly A tail
A tail of A-nucleotides, generally 100-200 long, is added to the 3'-end of most eukaryotic pre-mRNAs. The poly A tail, which is not coded in the DNA, is also retained in the mRNA exported to the cytoplasm.