Anonymous
06-04-2004, 10:08 PM
Problem 3: Why do pre-mRNAs get smaller during RNA processing?
The primary RNA transcript of the chicken ovalbumin gene is 7700 nucleotides long, but the mature mRNA that is translated on the ribosome is 1872 nucleotides long. This size difference occurs primarily as a result of:
A. capping
B. cleavage of polycistronic mRNA
C. removal of poly A tails
D. reverse transcription
E. splicing
The ovalbumin gene
The ovalbumin gene has been extensively studied. This gene is known to have 8 exons which encode the mature ovalbumin mRNA coding sequences. These 8 exons are interrupted by 7 introns, which are non-coding sequences that are transcribed into the ovalbumin precursor mRNA. During splicing of the pre-mRNA in the nucleus, the 7 introns, which account for 5828 (76%) of the pre-mRNA, are removed and the exons are joined together to yield a mature mRNA of length 1872 nucleotides.
A diagram of the pre-mRNA processing pathway is shown below:
http://www.biology.arizona.edu/molecular_bio/problem_sets/mol_genetics_of_eukaryotes/graphics/03t.gif
ans:
E. splicing
Splicing of the pre-mRNA removes 7 introns which total 5828 nucleotides of the pre-mRNA sequence.
The primary RNA transcript of the chicken ovalbumin gene is 7700 nucleotides long, but the mature mRNA that is translated on the ribosome is 1872 nucleotides long. This size difference occurs primarily as a result of:
A. capping
B. cleavage of polycistronic mRNA
C. removal of poly A tails
D. reverse transcription
E. splicing
The ovalbumin gene
The ovalbumin gene has been extensively studied. This gene is known to have 8 exons which encode the mature ovalbumin mRNA coding sequences. These 8 exons are interrupted by 7 introns, which are non-coding sequences that are transcribed into the ovalbumin precursor mRNA. During splicing of the pre-mRNA in the nucleus, the 7 introns, which account for 5828 (76%) of the pre-mRNA, are removed and the exons are joined together to yield a mature mRNA of length 1872 nucleotides.
A diagram of the pre-mRNA processing pathway is shown below:
http://www.biology.arizona.edu/molecular_bio/problem_sets/mol_genetics_of_eukaryotes/graphics/03t.gif
ans:
E. splicing
Splicing of the pre-mRNA removes 7 introns which total 5828 nucleotides of the pre-mRNA sequence.