167. Given below are two statements:
Statement I: Large subunit of rubisco is encoded by chloroplast genome while small subunit of
Rubisco is encoded by nuclear genome
Statement II: Small subunit of rubisco has a transit peptide, which is cleaved off at the time of its
translocation into plastids.
Choose the correct answer from the options given below:
A. Both Statement I and Statement II are true
B. Both Statement I and Statement II are false
C. Statement I is true but Statement II is false
D. Statement I is false but Statement II is true

Introduction Biogenesis of Rubisco: The Role of the Large and Small Subunits

Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) is one of the most important enzymes in photosynthesis, responsible for carbon fixation. It is composed of a large subunit and a small subunit, and understanding how these subunits are synthesized and assembled is crucial for understanding the enzyme’s role in plant metabolism. There is an interesting aspect of rubisco biogenesis involving the chloroplast genome and the nuclear genome. This article explains the statements regarding the encoding and processing of rubisco subunits.

Statement Analysis

Statement I: The large subunit of rubisco is encoded by the chloroplast genome, while the small subunit of rubisco is encoded by the nuclear genome.

• The large subunit of rubisco is indeed encoded by the chloroplast genome. This subunit is synthesized within the chloroplast and plays a crucial role in the enzyme’s carboxylation reaction.

• The small subunit, however, is encoded by the nuclear genome, synthesized in the cytoplasm, and then imported into the chloroplast where it combines with the large subunit to form the functional enzyme.

Statement II: The small subunit of rubisco has a transit peptide, which is cleaved off at the time of its translocation into plastids.

• The small subunit of rubisco does indeed contain a transit peptide that directs the protein to the chloroplasts. Once the small subunit reaches the chloroplast, the transit peptide is cleaved off during translocation, allowing the protein to mature and participate in rubisco assembly.

Conclusion

Both statements are correct, as explained above. Therefore, the correct answer is:

A. Both Statement I and Statement II are true.

This confirms that the large subunit is encoded by the chloroplast genome, the small subunit by the nuclear genome, and the presence of a transit peptide in the small subunit that is cleaved during plastid translocation.