Question

Pyrenoids are made up of
(a) Core of starch surrounded by sheath of protein
(b) Core of protein surrounded by fatty sheath
(c) Proteinaceous center and starchy sheath
(d) Core of nucleic acid surrounded by protein sheath

Answer 1

Hint: Pyrenoids are the subcellular micro-compartments or simply the dense bodies of some algae and other plants within the chloroplast. Pyrenoids consist of biomolecules that have one or more amino acids and a polysaccharide.

Complete step by step answer:
Pyrenoids consist of a protein-like central, viscous granular core and this core is surrounded by tightly packed minute plates, called starch plates or starch cells. Pyrenoids are composed of a dense proteinaceous region surrounded by a starchy sheath. These are unique to algae chloroplast and are related to polymerizing sugars into starch (reserve polymers).
At the periphery of pyrenoids, a starch sheath is often formed or deposited, also though that starch is synthesised in the cytosol rather than in the chloroplast. An additional concentric layer around the pyrenoid, beyond the starch sheath, forms a high-molecular weight complex of two proteins in Chlamydomonas, and this is currently speculated to serve as a ${ CO }_{ 2 }$ leakage barrier or barrier to recapture ${ CO }_{ 2 }$ that keeps escaping from the pyrenoid.
So, the correct answer is, ‘Proteinaceous center and starchy sheath’.

Additional Information:
The pyrenoids are associated with the carbon-concentrating mechanism to serve as carbon dioxide fixation centers by producing and sustaining an atmosphere rich in carbon dioxide around the ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo) photosynthetic enzyme. Thus, pyrenoids seem to have an analogous function to that of cyanobacterial carboxysomes. It is considered as the site of starch formation.


Note: Many bryophytes and algae show pyrenoids. They are tiny spherical bodies which are located in a plant cell's cytoplasm. They are rich in proteins and covered by a sheath of starch. The central protein mass is known as pyreno-crystal. There is a significant overlap between algal species in the pyrenoid morphology and ultrastructure.