A scientist discovered a noble gene from cancer cells and found to be associated

Question

A scientist discovered a noble gene from cancer cells and found to be associated with development of cancerous of cells. The nucleotide sequence of the template strand was determined as written below. study the sequence and answer the following questions. 3' GACACGTAC GAGCCTG s' A. write down the sense strand of the gene showing direction. B. Write down the nucleotide sequence of the mRNA. C. How many amino acids will be in polypeptide produced from this mRNA? Write down the amino acid sequence of the polypeptide. D. Write down the sequence of the neucleotides of the DNA fragments produced from the gene after EcoRI digestion. E. Write down the sequence of the neucleotides of the mRNA produced from the gene after EcoRI digestion.

Explanation / Answer

A) Sense strand is the one which is complimentary to the antisense strand (This is given in the problem). Sense strand runs 5’ to 3’.
So the sequence would be this:
5’ CTGTGCATGCTCGGACCTGTGGAATTCTCGCCCGAGCCTTGTGACCGGGGCTAACTGTG 3’

B) mRNA is made from the template strand. So its sequence will be the same as sense strand, only the T (Thymine) will be replaced by U (Uracil) :
5’ CUGUGCAUGCUCGGACCUGUGGAAUUCUCGCCCGAGCCUUGUGACCGGGGCUAACUGUG 3’

C) Not all regions in in the mRNA are translated. Translation begins from the AUG codon, also known as the start codon. I have underlined the start codon in the mRNA sequence above. I have used the Universal Genetic Code Chart to find which codon codes for which amino acid. So starting from AUG, which codes for methionene, the translation goes till a stop codon is encountered (UAA, UAG, UGA). Following is the amino acid sequence:
MET - LEU - GLY - PRO - VAL - GLU - PHE - SER - PRO - GLU - PRO - CYS - ASP - ARG - GLY
There are 15 amino acids in the sequence.
Note: I have used three letter abbreviations of the amino acids.

D) Following is the genetic sequence:
5’ CTGTGCATGCTCGGACCTGTGG^AATTCTCGCCCGAGCCTTGTGACCGGGGCTAACTGTG 3’
3' GACACGTACGAGCCTGGACACCTTAA^GAGCGGGCTCGGAACACTGGCCCCGATTGACAC 5'
EcoR1 restriction site is indicated by " ^ " below:
5' G^ AATTC 3'
3' CTTAA^ G 5'
Resulting fragments are (I have highlighted the restriction site in genetic sequence):
i) 5’ CTGTGCATGCTCGGACCTGTGG 3'
3' GACACGTACGAGCCTGGACACCTTAA 5'
ii) 5' AATTCTCGCCCGAGCCTTGTGACCGGGGCTAACTGTG 3’
3' GAGCGGGCTCGGAACACTGGCCCCGATTGACAC 5'

E) EcoRI is a restriction enzyme that can digest only DNA duplexes. It cannot digest an mRNA strand as its restriction site is not present.

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