1. You are studying a mRNA found in E. coli that appears to encode two separate
ID: 211575 • Letter: 1
Question
1. You are studying a mRNA found in E. coli that appears to encode two separate polypeptides (there are two separate starting points of translation). You would like to make these same proteins by putting this mRNA into a human cell. Assuming you have the ability to make any RNA molecule with a particular sequence, what RNA(s) would you synthesize to be able to express the two polypeptides in a human cell. Describe what you would need to add or remove to the RNA(S) 2. What are polyribosomes and are they found in eukaryotes or prokaryotes? 3. Which site within the ribosome is the tRNA found that is attached to the elongating polypeptide? 4. The following E. coli mRNA (only the coding portion of the native mRNA is shown) is shown below where the first three bases form the start codon and the last three the stop codon AUGGCGGAGCCGCGAUAG You have isolated several mutant strains that have variants of this mRNA because of mutations. Please determine whether each mRNA possesses silent, A. AUGGCGUAGCCGCGAUAG B. AUGGCGGAGCCGCGGUAG C. AUGGAGGAGCCGCGAUAG Name Recitation Section, D. AUGGGCGGAGCCGCGAUAGExplanation / Answer
2) Polyribosomes or polysomes are the cluster of ribosomes bound to single mRNA, that synthsizes single protein.
Polysomes are found either free in the cytoplasm (in prokaryotes) or attached to the surface of membranes of the endoplasmic reticulum (ER) and the nucleus (in eukaryotes)
3) During elongation, the tRNA attached to the growing peptide chain is on the P-site of the small ribosomal subunit. A peptide bond is formed between the amino group of the A site amino acid and the carboxyl group of the most-recently attached amino acid in the growing polypeptide chain attached to the P-site tRNA
4) a) AUG GCG UAG CCG CGA UAG - This mRNA has non sense mutation as a stop codon is present in the middle of reading frame.
AUG GCG GAG CCG CGA UAG
b) AUG GCG GAG CCG CGG UAG - Silent mutation as codons CGA and CGG codes for arginine
C) AUG GAG GAG CCG CGA UGA - Missense mutation as GCG in unmautated mRNA codes for alanine whereas in mutated mRNA GAG codes for glutamate
D) AUG GGC GGA GCC GCG AUA G - Frameshift mutation as an extra nucleotide 'G' (just after start codon) is inserted in the mRNA results in the shift in translational reading frame.
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