AIIMS 2005 Botany Gene Expression Assertion Reason Question

To address the question regarding the assertion and reason related to protein synthesis, we need to carefully evaluate both statements and their relationship.

Assertion

The assertion states: "Replication and transcription occur in the nucleus but translation occurs in the cytoplasm."

• Replication: This is the process of copying DNA to produce two identical DNA molecules. This occurs in the nucleus because DNA is housed there.

• Transcription: This is the process where a segment of DNA is copied into mRNA (messenger RNA). This also takes place in the nucleus since the DNA template is located there.

• Translation: This is the process where the mRNA is translated into a protein at the ribosomes, which are located in the cytoplasm. Thus, translation occurs outside the nucleus.

So, the assertion is indeed true.

Reason

The reason states: "mRNA is transferred from the nucleus into the cytoplasm where ribosomes and amino acids are available for protein synthesis."

• After transcription, the mRNA, which carries the genetic information from DNA, is processed (including splicing and capping) and then exported from the nucleus into the cytoplasm.
• In the cytoplasm, ribosomes (which may be free or attached to the endoplasmic reticulum) read the mRNA sequence and facilitate the assembly of amino acids into a polypeptide chain, which ultimately folds into a functional protein.

This reason is also true and provides a correct explanation of why the assertion is accurate. The movement of mRNA from the nucleus to the cytoplasm is essential for translation to occur, linking the two processes of transcription and translation.

Conclusion

Since both the assertion and reason are true, and the reason correctly explains the assertion, the correct answer is:

A) If both Assertion & Reason are true and the reason is the correct explanation of the assertion.

Why Other Options Are Incorrect

Let’s evaluate why the other options are not suitable:

• B) If both Assertion & Reason are true but the reason is not the correct explanation of the assertion.
  This is incorrect because the reason given does indeed explain the assertion.

• C) If Assertion is true statement but Reason is false.
  This is incorrect because both the assertion and reason are true.

• D) If both Assertion and Reason are false statements.
  This is incorrect since both statements are true.

Summary

In summary, the assertion correctly identifies the locations of replication, transcription, and translation, while the reason accurately describes the process of mRNA transfer and its role in protein synthesis. Therefore, option A is the only correct choice.

This clear relationship between the assertion and reason solidifies our understanding of gene expression at a molecular level, which is crucial for any student preparing for exams like NEET or JEE.