Ribosome is a non membrane cell organelles. it also know as protein factory of cell.. it was discovered by Emil Palade. It presents both in eukaryotes and prokaryotes. It has a major role in protein synthesis .

1. Ribosome

2. Introduction :
• One of the essential cell organelles are Ribosome.
• They are non-membraneous organelles that means they don’t include any phospholipid membrane.
• Ribosome is a large complex molecule made up of rRNA and Protein.
• It is the site of protein synthesis thus it called protein factory of cell.
• Ribosomes are free in the cytoplasm and often attached to the membrane of the endoplasmic
reticulum.
• Ribosomes are found in all living cells eukaryotic as well as prokaryotic.
• Eukaryotic cells have 80S Ribosome and prokaryotic cells have 70S Ribosome.
• The number of Ribosome per cell varies , it may be 10000 (in bacterial cell) or upto 10 million
(eukaryotic cell).

3. Discovery :
• Ribosomes were first observed in the mid 1950s by George Emil Palade, as dense particles or
granules. The term 'ribosome’ was first proposed by Richard B. Roberts.

4. Location:
• Ribosomes are exist in both eukaryotic and prokaryotic cell
• They are situated in the cytsol, (free Ribosome) some are bound to the membrane of the rough
endoplasmic reticulum (called membrane bound ribosome ).

5. • In an animal or human cell , there could be up to 10
million ribosomes and numerous ribosomes can be
connected to the equivalent mRNA strand , this
structure is known as Polysomes.
• In eukaryotes, ribosomes are also present in
mitochondria and in plastids such as chloroplast .

6. Size:
• Prokaryotic ribosomes are about 20 nm in diameter and are made up of 35%
ribosomal protein and 65% rRNA.
• Eukaryotic ribosomes are about 30 nm in diameter.
Structure :
• Prokaryotic subunits
• Larger subunit 50S
• Smaller subunit 30S
• Total ribosomal complex 70S
Eukaryotic subunits
• Larger subunit 60S
• Smaller subunit 40S
• Total ribosomal complex 80S
• Eukaryotic cell has almost 78 proteins

9. Svedberg units :
It is the centrifugal unit depending on the density of the object determining that how
quickly they sink to the depth when centrifuged. It also called sedimentation
coefficient.
Biogenesis :
In prokaryotic cell ribosome are synthesized in cytoplasm through the transcription of
multiple ribosomal gene operon.
In eukaryotes the process takes place in both the cell cytoplasm and the nucleolus.

10. Function :
The important ribosome function includes:
It assembles amino acid to form proteins that are essential to carry out cellular functions.
The DNA produces mRNA by the process of DNA transcription.
The mRNA is synthesized in the nucleus and transported to the cytoplasm for the process of protein synthesis.
The ribosomal subunits in the cytoplasm are bound around mRNA polymers. The tRNA then synthesizes proteins.
The proteins synthesized in the cytoplasm are utilized in the cytoplasm itself, the proteins synthesized by bound
ribosomes are transported outside the cell.

11. Syed Rumman Alam
Guskara Mahavidyalaya
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