Question

Photosynthesis is a process that takes place within the chloroplast of the A. titanium plant and this process requires a lot of proteins and various enzymes that are produced by cytosolic ribosomes. Explain, briefly, the process and specialized features that these proteins must have/undergo to make their way to the chloroplast. (2-3 sentences).

Answer 1

Chloroplast has its on genome and synthesises a few of its own proteins. However, majority of its proteins are produced in the cytosolic ribosomes and are translocated into the different components of the chloroplast. The proteins that are to be sent to the chloroplast contain a 30-100 aminoacid long transit peptide which helps their translocation into the stroma through the TIC and TOC complexes on the outer and inner memberane of the chloroplast respectively. Once they reach the stroma, the transit peptide is cleaved. If the proteins are to be further taken to the thylakoid, the cleavage of transit peptide leads to the exposure of another hydrophobic signal sequence, that helps in the transit of the protein across the thylakoid memberain into the lumen. In this manner, proteins and enzymes required for photosynthesis are transported from cytosolic ribosomes to the compartments of the chloroplast.