Question

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.

Hint:

To calculate the contour length of DNA, determine the number of base pairs and multiply by the rise per base pair (for B-DNA, 0.34 nm).

Answer 1

Correct Answer: 300

Step 1: Calculate the number of amino acids in the protein.
The molecular weight of the protein is 33 kDa, which is equivalent to 33,000 Da. Since the average molecular weight of an amino acid is 110 Da, the number of amino acids in the protein is: \[ \frac{33,000 \, {Da}}{110 \, {Da/amino acid}} = 300 \, {amino acids}. \] Step 2: Calculate the number of base pairs encoding the protein.
Each amino acid is encoded by 3 base pairs (codon). Therefore, the number of base pairs required to encode the protein is: \[ 300 \, {amino acids} \times 3 \, {base pairs/amino acid} = 900 \, {base pairs}. \] Step 3: Calculate the contour length of the DNA.
The rise per base pair for B-DNA is 0.34 nm. Therefore, the contour length of the DNA that encodes the protein is: \[ 900 \, {base pairs} \times 0.34 \, {nm/base pair} = 306 \, {nm}. \] Thus, the contour length of the DNA molecule is \( \boxed{306} \, {nm} \).