Question

What should be the approximate molecular weight of the heavy chain of human IgG if the variable region is 110 amino acid long and constant region is three-times the variable region?

• A. 11 KDa
• B. 19 K Da
• C. 48 KDa
• D. 37 KDa

Hint:

IgG Heavy Chain MW Calculation: $440\text{ aa} \times 110\text{ Da/aa} = 48.4\text{ kDa} \approx 48-50\text{ kDa}$. Light chain $\approx 25\text{ kDa}$, Total IgG monomer $\approx 150\text{ kDa}$.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Protein molecular mass estimation uses the average molecular weight of an amino acid residue ($pprox 110 ext{ Da}$) multiplied by total chain residue count.
Key Formula or Approach:
\[ \text{Total Residues} = N_{V_H} + N_{C_H} = 110 + 3(110) = 440\text{ amino acids} \]
\[ \text{Molecular Weight} \approx 440 \times 110\text{ Da} = 48,400\text{ Da} \approx 48\text{ kDa} \]

Step 2: Detailed Explanation:
Given domain parameters:
- Variable region ($V_H$) length = $110\text{ amino acids}$.
- Constant region ($C_H1 + C_H2 + C_H3$) length = $3 \times 110 = 330\text{ amino acids}$.
- Total heavy chain length = $110 + 330 = 440\text{ amino acids}$.
- Using standard mean molecular weight per amino acid residue of $110\text{ Da}$:
\[ \text{Approximate MW} = 440 \times 110 = 48,400\text{ Da} = 48.4\text{ kDa} \approx 48\text{ kDa} \]

Step 3: Final Answer:
Hence, the approximate molecular weight of the heavy chain is 48 KDa, corresponding to option (C).