Question

Define Ribophorin and what are their functions?

Answer 1

Ribophorins are characteristic trans-membrane structural glycoproteins on the rough endoplasmic reticulum. There are two characteristic structural glycoproteins in the rough endoplasmic reticulum, namely Ribophorin I and II.

Complete answer:
Ribophorins are Ribosome receptor proteins on the rough endoplasmic reticulum. They serve as binding sites for ribosomes and also mediate the binding of Ribosomes with the rough endoplasmic reticulum. They interact with each other and form a network within the membrane to control the distribution of ribosome binding sites. They are ribosome receptor proteins that help in the binding 60S subunit of eukaryotic ribosomes to the rough endoplasmic reticulum. There are two characteristic Ribophorin on RER namely, Ribophorin I and Ribophorin II.

Additional Information:
-The members of ER have lipoprotein composition and fluid mosaic organization. They are formed mostly of phospholipids, cholesterol, and intrinsic and extrinsic proteins.
-Cholesterol binds with this bilayer to form a stable complex. Intrinsic proteins partially or completely penetrate the lipid bilayer, whereas extrinsic proteins remain entirely outside the lipid bilayer.
-Intrinsic proteins are mostly structural, and extrinsic proteins are mostly enzymatic.

Note:
-Endoplasmic reticulum is a vast network of membrane-bound, branching, and interconnecting tubules, vesicles, and flattened sacs, irregularly distributed in the cytoplasmic matrix.
-With the exception of prokaryotes and mature mammalian erythrocytes, it is present in almost all kinds of cells. It is only poorly developed in egg cells and sperm cells. ER is a complex system of membrane-bound spaces.
- These spaces are filled with a fluid, rich in enzymes, metabolites, and synthetic products. They are of two kinds namely smooth endoplasmic reticulum and Rough endoplasmic reticulum. RER has attached ribosomes, SER has no attached ribosomes. RER is a major location for the synthesis of secretory or export proteins.