Ribosomes Functions, Structure and Characteristics

Ribosomes are tiny granular structures. Palade was the first person, who studied them in 1955. Ribosomes are small bodies, either attached to the endoplasmic reticulum or found freely in the cytoplasm. These are composed of RNA and Protein. They are called protein factories because they take part in protein synthesis.

Chemical Composition

The ribosome of the eukaryotic cells is composed of ribonucleoproteins. The ribonucleoprotein contains an equal amount of RNA and protein. The RNA in the ribosome is ribosomal RNA.

Occurrence of RibosomeRibosomes

They are present in two forms:

  1. Freely dispersed form, in the cytoplasm.
  2. Attached to REP as tiny granules,

Sub-Units of Ribosomes

The ribosome of the eukaryotes consists of two sub-units. The larger subunit is the 60S subunit. The small subunit is the 40S. “S” is Svedberg Unit. It is the rate of sediment formation during ultra-centrifugation. These two sub-units attach with each other to form 80S particles. This attachment is controlled by Mg2+ ions. The 40S subunit controls the attachment of the ribosome with mRNA.


A group of ribosomes attached to the same mRNA is known as Polysomes.

Formation of Ribosome

Each Ribosome consists of two parts; a large subunit is dome-shaped and a small subunit, which is present, like a cap on the larger part. Ribosomes are attached to the endoplasmic reticulum by these larger parts. They are produced in the nucleolus (ribonucleic acid) and then these are transferred to the cytoplasm.


Ribosomes take part in process of protein synthesis. So, these are called protein factories.

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