Question

What are the roles of the endoplasmic reticulum and ribosomes in protein synthesis?

Answer 1

Protein synthesis is the biological process of replacement of the proteins lost by the cells through the production of new proteins.
The ribosomes and the molecules associated with the ribosomes are collectively called the translational apparatus.

Complete answer:
Ribosomes are macromolecules present in biological cells. Ribosomes perform protein synthesis in a biological cell. Ribosomes link together amino acids according to the order provided by the codons of the messenger RNA to the ribosomes. These ribosomes form polypeptide chains. A ribosome is made up of two major parts, namely:
- The small ribosomal subunit
- The large ribosomal subunit
The endoplasmic reticulum is a type of cell organelle made up of two subunits, namely:
- Rough endoplasmic reticulum (RER)
- Smooth endoplasmic reticulum (SER)
The endoplasmic reticulum is the transportation system of an eukaryotic cell.
Cisternae are an interconnected network of flattened sacs enclosed by a membrane. Cisternae are formed by the endoplasmic reticulum.
The membranes of the endoplasmic reticulum are connected with the outer nuclear membranes. The endoplasmic reticulum is absent in the red blood cells and sperm cells.
The two subunits of the endoplasmic reticulum perform various functions like the synthesis of cholesterol or lipids. They also share the same proteins. The ratio of the two subunits of the endoplasmic reticulum differs in cells according to their functions.

Note:
Cisternae are found in most eukaryotic cells. The cisternae are flattened sac-like structures in the rough endoplasmic reticulum and are tubular structures in the smooth endoplasmic reticulum.
Each of the two subunits contain one or more ribosomal RNA molecules called rRNA. They also contain several ribosomal proteins called r-proteins.