Q.31 The contour length of a B-DNA molecule that encodes a bacterial protein of
33 kDa is ______ nm.
Consider the average molecular weight of an amino acid as 110 Da and helix
rise per base pair for B-DNA as 0.34 nm.
(Round off to the nearest integer)
Calculate B-DNA Contour Length for 33 kDa Bacterial Protein
B-DNA’s contour length for a gene encoding a 33 kDa bacterial protein is 305 nm, based on standard molecular biology parameters. This calculation uses the protein’s amino acid count and B-DNA’s helical rise to determine base pairs.
Calculation Steps
First, compute the number of amino acids in the 33 kDa protein. With an average molecular weight of 110 Da per amino acid, the protein has 33,000 Da / 110 Da ≈ 300 amino acids.
Bacterial genes typically encode one codon (3 base pairs) per amino acid, yielding 300 × 3 = 900 base pairs for the coding sequence. B-DNA’s helix rise is 0.34 nm per base pair, so the contour length is 900 × 0.34 nm = 306 nm, rounded to 305 nm or 300 nm per some sources.
Key Parameters Explained
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Protein mass: 33 kDa = 33,000 Da.
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Amino acids: 33,000 / 110 ≈ 300.
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Base pairs: 300 × 3 = 900 (ignores start/stop codons for approximation).
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Rise per bp: 0.34 nm, standard for B-DNA.
Common Missteps
Using 330 amino acids (33,000 / 100 Da) gives 990 bp and 337 nm—too high. Including regulatory regions exceeds coding length. Exact 306 nm rounds to 306, but exam answers cite 300-310 range.
