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

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:
\[ \frac{33,000 \, \text{Da}}{110 \, \text{Da/amino acid}} = 300 \, \text{amino acids} \]
Step 2: Calculate the number of base pairs encoding the protein.
Each amino acid is encoded by 3 base pairs (1 codon). So the number of base pairs required is:
\[ 300 \, \text{amino acids} \times 3 \, \text{bp/amino acid} = 900 \, \text{base pairs} \]
Step 3: Calculate the contour length of the DNA.
For B-DNA, each base pair contributes 0.34 nm to the contour length. Therefore:
\[ 900 \, \text{base pairs} \times 0.34 \, \text{nm/base pair} = 306 \, \text{nm} \]
Final Answer:
The contour length of the DNA molecule encoding this protein is \( \boxed{306} \, \text{nm} \).