The ribosome is found independently in the cytoplasm and as a rash on the rough endoplasmic reticulum. The ribosome is found in all cells except RBC cells (eukaryotic cells and prokaryotic cells). Is the smallest cell unit.

What is the function of Ribosomes? Types, Definition, and Structure

Ribosome explorers 

  • Robinson and Brown (in bean roots)
  • Nominee – Palade (seen as dense granules by electronic microscope)

About Ribosomes

First seen by George Palade. It is absent in mature RBCs. It is the smallest cell in size. Its size is 15–20nm.

Ribophorin is present on RER (rough endoplasmic reticulum) with the help of proteins. They are also found in the nucleolus (nucleus) of the cell and are also found in the cytoplasm of all cells.

What is the function of Ribosomes? Types, Definition, and Structure

Characteristics of Ribosomes

They have the following characteristics:

  1. These are membrane-less.
  2. They are spherical.
  3. The smallest cell is.
  4. They have a diameter of 150– 250 Å.
  5. It is made of riboprotein and mRNA.
  6. It is found in the cytoplasm, mitochondria, nucleus, endoplasmic reticulum, green leaves.
  7. Their size is determined based on the sedimentation coefficient.

Types of Ribosome

It is of the following type –

  • Found in both prokaryotic cells and eukaryotic cells.
  • Ribosome type 70S is found in the prokaryotic cell which is made up of unit 16S type of large subunit 50S and unit 25S + 5S and unit of small subunit 30S.
  • In the eukaryotic cell, ribosomes are found to be of the 80S type, which is made up of the larger sub-unit 60S unit (28S + 5.8S + 5S) and the smaller sub-unit 40S as the unit 18S.

Note: – 

  • s = sedimentation coefficient (is the unit of measure of the size of the ribosome)
  • The ribosome of mitochondria and chloroplast is found to be of type 70S.
  • Ribosomes of mitochondria are known as mitoribosomes.
  • The ribosome of the chloroplast is called the plastidial ribosome.

Prokaryotic Ribosome

Ribor som 70s are of the type in a prokaryote. Which are made up of the 50s and 30s subunits.

Eukaryotic Ribosome

Ribosomes in the eukaryote are of the 80s type. The 60s and 40s are made up of subunits.

Chloroplast Ribosome

It is of 70s type which is made up of 50s and 30s subunits.

Mitochondria ribosomal (Mitochondrial Ribosome)

It is of 70s type which is made up of 50s and 30s subunits.

Structure of Ribosome

According to the sedimentation unit, there are two subunits of the ribosome. Its large subunit is oval in shape and the smaller subunit is oval.

Its large sub-unit consists of three sites.

  1. A-Site: – It is the aminoacyl site and the receptor site for T-RNA.
  2. P-Site: – This peptide site is the site for elongation of the peptide chain.
  3. E-Site: – This is the site for T-RNA to exit the ribosome.

Its subunits are made by riboprotein and R-RNA. Which are as follows –

  1. 50s subunit – 34% protein + 23S and 5S rRNA
  2. 30s subunit – 21% protein + 16S rRNA
  3. 60s subunit – 40% protein + 28S, 5.8S and 5S R-RNA
  4. 40s subunit – 33% protein + 18S rRNA

The ribosome is formed by 40–60% protein and 60–40% RNA in the nucleolus (nucleus). The nucleolus is considered the Ribosomal Manufacturing Factory.

What is the function of Ribosomes?

The main function of ribosomes

Translation in biology

The process of formation of a protein is called translation. It participates in protein synthesis, hence it is known as the engine or protein factory of the cell. This is called the Protein Factory of the Cell.


During protein synthesis, several ribosomes bind to M-RNA to form a structure, called a polyribosome or poly seam.

What Is The Sedimentation Coefficient And What Does S Mean?

A Special Type Of Device Is Used For The Study Of Ribosomes. It Is Used And It Is Called Ultracentrifuge. A Special Type Of Ribosome Solution Is Poured Into The Tubes Of This Device And Rotated With Great Speed. Ribosomes Of Different Sizes Set At The bottom Of the tube At Different Speeds. This Speed Is Called The Sedimentation Coefficient. And Its Speed Measuring Unit Is The Svedberg Unit. Which Is Represented By S. And This Is The Unit To Measure The Sedimentation Coefficient.

What is the function of Ribosomes? Types, Definition, and Structure


Categories: Cell Biology