1. You have discovered a novel sigma factor in coli cells called ?25 Based on da
ID: 217855 • Letter: 1
Question
1. You have discovered a novel sigma factor in coli cells called ?25 Based on data from a DNase foot-printing assay you have determined that ?25 binds to consensus sequences at positions 15 and -30 upstream of genes involved in the stress response to lambda bacteriophage infections, including gene z. You hypothesize that in order for gene z to be transcribed the ?25 protein must bind to the -15 and -30 regions. What approach could you use to test this hypothesis? You have already cloned the promoter region (containing the -15 and -30 regions) and the coding region for gene z into pUC19. What molecular techniques could you use to test your hypothesis? What results would you need to get to support your hypothesis? (4 points) dependent termination (2 points). 3. Given the wobble base pairing, only 9 tRNAs are needed to encode the 4 amino acids Ser, Pro, Trp, and Leu. List the mRNA codons for the 4 amino acids and necessary 9 tRNA anti-codons. (4 points) 4. What is the amino acid sequence of the peptide encoded by the following mRNA sequence? Which positions in the mRNA can tolerate a mutation without resulting in a change in amino acid sequence? What changes are tolerated at each of these positions? (2 points) 5-AUGACCAAAUGGGCG-3'Explanation / Answer
Q.3
Serine
mRNA codon: UCU, UCC, UCA, UCG, AGU, AGC.
tRNA codon: AGA, AGG, AGU, AGC, UCA, UCG.
Proline
mRNA codon: CCU, CCC, CCA, CCG.
tRNA codon: GGA, GGG, GGU, GGC.
Tryptophan
mRNA codon: UGG
tRNA codon: ACC
Leucine
mRNA codon: UUA, UUG, CUU, CUC, CUA, CUG
tRNA codon: AAU, AAC, GAA, GAG, GAU, GAC
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Q.4
NH3- Met-Thr-Lys-Trp-Ala -COO-
Cells can tolerate mutation at the third base pair position of a codon triplet. For eg. Alanine can be coded GCA, GCU, GCG, GCC. A change/mutation in the third base pair position of the codon will not affect the amino acid sequence. Such kind of mutations are synonymous codon mutation.
But a change in the first or second base pair position of codon triplet will change the amino acid sequence. Such a kind of mutation can be lethal and cant be tolerated.
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