Ribosome ,polysome structure and function

1. Structure & Function of Ribosome
Dr. Sonia Bajaj, (Head of Department)
Shri Shankaracharya Mahavidyalaya, Junwani , Bhilai

2. Introduction
Cell have tiny granular structures known as Ribosomes.
Ribosomes are known as the protein makers of all cells. Proteins control and
build life.
Robinson and Brown (1953) in plant cells and by Palade (1955) in animal cells.
Palade (1955) also coined the term of ribosome.
smallest organelles of the cell are the without any unit membrane
Found in prokaryotic & Eukaryotic cells
Except-Mature sperm &Mature Mammal RBC
Also in organelle- Mitrochondria & Plastides
In cytoplasm – Free Ribosome
On the Membranes –ER & Nucleous –Bounded Ribosome
The S stand for Svedberg unit.

3. Ribosomes are made up of rRNA and protein.
The ratio of rRNA and protein in 70s ribosome is 1.5 : 1.
The ratio of rRNA and protein is 80s ribosome is 1 : 1.
Mg2+ ion concentration of 0.001 M .
Many Ribosome become attached to mRNA during protein synthesis,
this chain ribosome is known as Polysome.

4. Structure of Ribosome
large subunit-
It is dome shaped and is attached to ER .
It has a protuberance , branch a ridge and a stalk.
It has 3 main binding site, P site (peptidyl side or donor site) and A site (amino
acyl site or acceptor site). it is also has a E site exit side
large subunit is rich in Peptidyl Transferase Enzyme.
Small subunit –
It is oval and fits as a cap on the large subunit.
It has a platform, a cleft, a head and a base.
It has binding site for mRNA.

5. • Domains of Ribosomes
• Translational Domain: The region responsible for translation
is called the Translational domain Both subunits contribute to
this domain, located in the upper half of the small subunit and
in the associated areas of the large subunit .
• Exit Domain: The growing peptide chain emerges from the
large subunit at the exit domain . This is located on the side of
the subunit.

6. Types of Ribosome

7. Functions of Ribosomes
(i) Protein Factories: Ribosomes are sites for polypeptide or protein
synthesis. Protein Synthesis is divided into three stages: 1.
Initiation 2. Elongation 3. Termination
(ii) Free and Attached Ribosomes:
Free ribosomes synthesis enzymes for muscles , Skin cells, and
erythroblasts.
(iii) Enzymes and Factors:
Ribosomes provide enzymes (e.g., Peptidyl transferees) and factors for
condensation of amino acids to form polypeptide,
(iv) rRNA:
Ribosome also store rRNA .
(vi) Folding and transport protein is assisted by a special protein called
Chaperons.