the DNA sequence below represents exon 3 of a gene. How many possible open readi

Question

the DNA sequence below represents exon 3 of a gene. How many possible open reading frames (i.e., frames without any stop codons) extend through this sequence (remember that transcription can use either strand as a template)? The stop codons are UAA, UAG, and UGA. 5’-AAAGGTATGTTTCGAATGATACTAACATAACAAAGAACATTTTCAGGAGGACCCTTGGAGGGTACCGG-3’ 3’-TTTCCATACAAAGCTTACTATGATTGTATTGTTTCTTGTAAAAGTCCTCCTGGGAACCTCCCATGGCC-5’ 2) Suppose that the below sequence corresponds to part of the promoter and start of transcription of a eukaryotic gene. a) On the sequence, draw a possible start of transcription, indicate the direction of transcription, and label a +1. b) Which is the template strand and which is the RNA-like strand? 5’-CAAAGGTATGTTTCGAATGATACTAACATAACATAGAACATTTTCAGGAGGACCCTGGGCGGGTACCGGTAGA 3’-GTTTCCATACAAAGCTTACTATGATTGTATTGTATCTTGTAAAAGTCCTCCTGGGACCCGCCCATGGCCATCT AGGATAACATGGCCATCATCAATGAGTTCATGCGCTTCAAGGTGCACATGGAGGGCTCCGTGATATAAACACGAGTT TCCTATTGTACCGGTAGTAGTTACTCAAGTACGCGAAGTTCCACGTGTACCTCCCGAGGCACTATATTTGTGCTCAA TCCAAGGCCTACGTGAAGCACCCCGCCGACATCCCCGACTACTTGAAGCTGTCCTTCCCCGAGGGCTTCAAGT-3’ AGGTTCCGGATGCACTTCGTGGGGCGGCTGTAGGGGCTGATGAACTTCGACAGGAAGGGGCTCCCGAAGTTCA-5’ 3) GATGTAATCTAGTAGTCAACTGAGGTTCATCGCCTCCT Suppose the above DNA sequence is part of a template for RNA synthesis. a) Assuming that this template only includes exonic sequences, what is the maximum number of encoded amino acids? b) Suppose that the above sequence is the RNA-like molecule. Assuming that this segment only includes exonic sequences, what is the maximum number of encoded amino acids? 4) The following DNA sequence is transcribed and encodes a small protein with the sequence Met Cys Arg Asp Ala. 5'-CCTATGCCCGCATCATTACGCATCTCTGCACATGGGCCC-3' 3'-GGATACGGGCGTAGTAATGCGTAGAGACGTGTACCCGGG-5' a) Which strand of DNA is the template strand for transcription? Which strand is the coding strand? Which direction (right to left or left to right) does RNA polymerase move along the template as it transcribes this gene? b) A single base mutation in the gene results in synthesis of the peptide Met Cys. What is the sequence of nucleotides making up the protein encoding part of the mRNA produced by this mutant gene?

Explanation / Answer

3.Ans.

DNA template - 3'-GATGTAATCTAGTAGTCAACTGAGGTTCATCGCCTCCT-5'

RNA strand - 5'- CUACAUUAGAUCAUCAGUUGACUCCAAGUAGCGGAGGA - 3'

UAG and UGA acts as stop codons.the maximum number of amino acids translated from the above sequence is 2

b) if the above sequence is RNA like molecule means that sequence not act as template the complementary sequence acts as a template for synthesis of RNA.

5'-GATGTAATCTAGTAGTCAACTGAGGTTCATCGCCTCCT-3'

3'-CTACATTAGATCATCAGTTGACTCCAAGTAGCGGAGGA-5'

now the 3'-5' strand acts as a template for the synthesis of RNA strand.

DNA template 3'-CTACATTAGATCATCAGTTGACTCCAAGTAGCGGAGGA-5'

RNA strand - 5'-GAUGUAAUCUAGUAGUCAACUGAGGUUCAUCGCCUCCU-3'

so the maximum number of amino acids coded by sequence is 3 - Asp-Val-Ile.

4.Ans.

5'-CCTATGCCCGCATCA TTA CGC ATC TCT GCA CAT GGGCCC-3'

3'-GGATACGGGCGTAGTAATGCGTAGAGACGTGTACCCGGG - 5'

Template strand for transcription- 5'-CCTATGCCCGCATCATTACGCATCTCTGCACATGGGCCC-3'

RNA polymerase moves from Right to left for making the RNA

RNA strand - 5' - GGGCCCAUGUGCAGAGAUGCGUAAUGAUGCGGGCAUAGG-3'

CODING STRAND - 5'-AUGUGCAGAGAUGCGUAA-3'

CODES FOR - Met Cys Arg Asp Ala

Met Cys Arg Asp Ala     AUG UGC AGA GAU GCG UAA

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