Question:
Arrange the following heavy chain constant region genes of the immunoglobulin molecule from 5 prime to 3 prime in a correct order
A. IGHM
B. IGHD
C. IGHG
D. IGHE
E. IGHA
Choose the correct answer from the options given below:
Arrange the following heavy chain constant region genes of the immunoglobulin molecule from 5 prime to 3 prime in a correct order
A. IGHM
B. IGHD
C. IGHG
D. IGHE
E. IGHA
Choose the correct answer from the options given below:
A. IGHM
B. IGHD
C. IGHG
D. IGHE
E. IGHA
Choose the correct answer from the options given below:
Show Hint
The chronological appearance of immunoglobulins during B-cell ontogeny and the immune response closely reflects their physical 5' to 3' order on the chromosome: IgM $\rightarrow$ IgD $\rightarrow$ IgG $\rightarrow$ IgE $\rightarrow$ IgA.
Updated On: Aug 13, 2026
- A, B, C, D, E
- A, C, D, B, E
- A, D, E, C, B
- A, E, B, C, D
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The Correct Option is A
Solution and Explanation
Step 1: Understanding the Concept:
The constant heavy chain ($C_H$) genes of the immunoglobulin locus are arranged in a specific linear sequence along the chromosome.
This sequence runs from the 5' direction (closest to the rearranged variable VDJ regions) to the 3' direction.
This sequential arrangement is essential for class-switch recombination (CSR), where constant region genes are spliced out to change the antibody class.
Detailed Explanation:
In the immunoglobulin heavy chain (IGH) locus, the constant region gene segments are arranged from 5' to 3' as follows:
1. IGHM ($C_\mu$, encoding IgM): Located closest to the variable region. Naive B cells first transcribe and express IgM on their surface.
2. IGHD ($C_\delta$, encoding IgD): Positioned immediately downstream of $C_\mu$. Co-expression of IgM and IgD occurs via alternative splicing of a single primary RNA transcript.
3. IGHG ($C_\gamma$, encoding IgG): Positioned further downstream. Class-switch recombination to IgG deletes the intervening $C_\mu$ and $C_\delta$ segments.
4. IGHE ($C_\epsilon$, encoding IgE): Located downstream of the IgG gene segments.
5. IGHA ($C_\alpha$, encoding IgA): Located at the 3' end of the constant region locus.
Thus, the 5' to 3' sequence of heavy chain constant region genes is $C_\mu \rightarrow C_\delta \rightarrow C_\gamma \rightarrow C_\epsilon \rightarrow C_\alpha$, corresponding to the sequence A, B, C, D, E.
Step 2: Final Answer:
The correct order is A, B, C, D, E, which is Option (A).
The constant heavy chain ($C_H$) genes of the immunoglobulin locus are arranged in a specific linear sequence along the chromosome.
This sequence runs from the 5' direction (closest to the rearranged variable VDJ regions) to the 3' direction.
This sequential arrangement is essential for class-switch recombination (CSR), where constant region genes are spliced out to change the antibody class.
Detailed Explanation:
In the immunoglobulin heavy chain (IGH) locus, the constant region gene segments are arranged from 5' to 3' as follows:
1. IGHM ($C_\mu$, encoding IgM): Located closest to the variable region. Naive B cells first transcribe and express IgM on their surface.
2. IGHD ($C_\delta$, encoding IgD): Positioned immediately downstream of $C_\mu$. Co-expression of IgM and IgD occurs via alternative splicing of a single primary RNA transcript.
3. IGHG ($C_\gamma$, encoding IgG): Positioned further downstream. Class-switch recombination to IgG deletes the intervening $C_\mu$ and $C_\delta$ segments.
4. IGHE ($C_\epsilon$, encoding IgE): Located downstream of the IgG gene segments.
5. IGHA ($C_\alpha$, encoding IgA): Located at the 3' end of the constant region locus.
Thus, the 5' to 3' sequence of heavy chain constant region genes is $C_\mu \rightarrow C_\delta \rightarrow C_\gamma \rightarrow C_\epsilon \rightarrow C_\alpha$, corresponding to the sequence A, B, C, D, E.
Step 2: Final Answer:
The correct order is A, B, C, D, E, which is Option (A).
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