In every living being, cells need to make proteins. Enzymes that are made of proteins are used to help seed up the biological processes. Other proteins do support other cell functions and are found embedded in membranes. Proteins even builds up most of your hairs. When a cell requires to make proteins, it looks for ribosomes. Ribosomes are basically the proteins builders or we can say protein synthesizers. They can be thought just like construction guy, who connects one amino acid at a time and build long chains.


Ribosomes are very special because they are found in both eukaryotes and prokaryotes. While nucleus structure is only found in eukaryotes, every cell needs these ribosomes to manufacture proteins. In prokaryotes, there are no membrane-bound organelles, so ribosomes float freely is the cytosol.


Ribosomes can be found in many places around a eukaryotic cell. One might find them floating freely in the cytosol. Those floating ribosomes synthesizes proteins that will be used inside cell. Other ribosomes can be found on endoplasmic reticulum. Endoplasmic reticulum with attached ribosomes is known as rough ER. It looks bumpy when seen under a microscope. These attached ribosomes makes proteins that will be eventually used inside the cell and proteins made for export out of the cell. Some ribosomes are also attached to the nuclear envelope. These ribosomes synthesizes proteins which are released into the perinuclear space.


There are two pieces or we can say, two sub-units to every ribosome. In eukaryotes, scientists have seen and identified the 60-S (large) and 40-S (small) subunits. Even though ribosomes have somewhat slightly different structures in different species, there functions areas seems all very similar.


For example, ribosomes present in prokaryotes are smaller than those of eukaryotes. The 60-S/40-S model works very fine for eukaryotic cells while prokaryotic cells contains ribosomes made up of 50-S and 30-S subunits. It’s a very small difference but of many, we can find in the two different types of cells. Scientist have used this difference in the structure of ribosomes to develop drug that will be able to kill eukaryotic



Ribosomes are the site “Protein synthesis”.They are small sub-spherical granular organelles.It’s not enclosed by any membrane.They are composed of  ribonucleoproteins and rRNA.They occur in large number each of 150-250 Angstroms in diameter and consists of two unequal subunits, larger dome shaped and smaller ovoid one.


Ribosome by Benutzer:Sec11 (CC BY-SA)

Subunits occur separately only joins during protein synthesis.During protein synthesis many ribosomes line up and attached to mRNA to synthesize many copies of  polypeptides.Such bulk form of ribosomes are called Polysomes.

Why and how 70s,80s ribosomal subunits???

Based on the size and sedimentation co-efficient,ribosomes are of two types 70s and 80s.70s present mostly in prokaryotic cells whereas 80s(50s + 30s see image above) mostly found in eukaryotic cells.Sindicates Svedberg unit which is a measure of particle size during sedimentation through centrifuge.

Its origin…
In eukaryotic cells ribosomes are synthesized inside nucleolus.Ribosomal RNA are synthesized in the nucleolus.Ribosomal proteins are produced in cytoplasm and shift to the nucleolus.for the formation of ribosomal sub-units bu complexing with rRNA.Sub-units pass through nucleopores into cytoplasm for protein synthesis.
But in case of prokaryotes,both ribosomal RNA’s and proteins are synthesized in the cytoplasm.Hence it’s act as “Protein factories of the cell”.

Protein synthesis can be elaborately discussed later in Transcription and translation process….


Bacterial Ribosome:

During the synthesis of protein a ribosome moves along an mRNA molecule, reading the codon and then adding the correct amino acid (from the corresponding aminoacyl tRNA) to growing protein. When a stop codon is finally reached,translation ceases, and the corresponding protein and mRNA are released.

The bacterial ribosome is generally a cytoplasmic nucleoprotein particle whose primary function is to serve as a site of mRNA translation and the synthesis of protein. The ribosome has a mass approx. 2.5 MDa, with RNA which accounts for 2/3 of this mass. It also consists of two subunits denoted as 30S (small subunit) and 50S (large). When it is joined, the ribosome has the sedimentation coefficient of 70S as opposed to that of 80S due to tertiary structure. During the synthesis of protein a ribosome moves along an mRNA molecule, reading the codon and then adding the correct amino

Protein synthesis can be elaborately discussed later in Transcription and translation process….

By | 2015-08-23T16:25:02+00:00 March 26th, 2013|Cell organelles|0 Comments

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