1. A certain protein consisting of a single polypeptide chain has a molecular we
ID: 261483 • Letter: 1
Question
1. A certain protein consisting of a single polypeptide chain has a molecular weight of approximately 31,000. What is the best estimate for the molecular weight of the exons on the coding region (both strands), which programs the synthesis of this protein? The molecular weight of an average amino acid is 120 g/mol, and the average nucleotide molecular weight is 310 g/mol.
a. 72,000
b. 96,000
c. 124,000
d. 188,000
e. 236,000
f. 393,000
g. 480,000
h. 558,000
i. 603,000
The answer is g, but please explain how?
Explanation / Answer
Answer: Choice g
Explanation: As the molecular weight of the protein is 31000 Da, it must contain a total of 31000/120 or nearly 258 amino acids. Further, each amino acid is encoded by three set of nucleotides, thus the number of nucleotides required to encode these amino acids will be 258*3 or 774 nucleotides. Since molecular weight of one nucleotide is nearly 310g/mol, the average molecular weight of all these nucleotides will be 7744*310 or 239940. Since the exon is a segment of double stranded DNA containing two pairs of nucleotides each, this number would be double i.e. 239940*2 i.e. 479880 or nearly 480,000.
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