Ribosomes-Definition, Structure, Functions, And Diagram

Ribosomes Definition

  • The Greek words for “ribosome” were used to coin the terms “soma,” meaning “body,” and “ribo” from ribonucleic acid.
  • Most prokaryotic and eukaryotic organisms have ribosomes, which are small, spheroidal, dense particles with 150 to 200 A0 diameters.
  • They serve as protein production locations.
  • They are RNA and protein-containing structures that serve as a framework for the controlled interaction of the many parts participating in protein synthesis.
  • Prokaryotic and eukaryotic cells both include ribosomes.
  • Throughout the cytoplasm of prokaryotic cells, the ribosomes frequently move about freely.
  • Ribosomes in eukaryotic cells may either exist in the cytoplasm freely or can hang onto the membrane of the endoplasmic reticulum.
  • What sort of protein a cell produces depends on where the ribosomes are located inside the cell.
  • The cell will produce proteins that are used by the ribosomes if they are allowed to move around the cell.
  • Rough endoplasmic reticulum, or rough ER, is the name given to the endoplasmic reticulum when ribosomes are connected to it.
  • The proteins produced by the rough ER might be employed within or outside of the cell.
  • The number of ribosomes present in a cell is influenced by its activity.
  • A mammalian cell may have 10 million ribosomes on average.

Structure of Ribosomes

  • A ribosome is a ribonucleoprotein because it is constructed from complexes of RNA and proteins.
  • Approximately 37–62% of RNA is made up of RNA, while the remaining portion is made up of proteins.
  • Each ribosome consists of two separate subunits:
  1. Smaller subunit:There is a bigger component that interacts with the smaller subunit, tRNA, and amino acids.
  2. Largersubunits: Prokaryotes contain 70S ribosomes, or subunits, which are made up of the smaller 30S and larger 50S subunits.
  • A 16S RNA subunit from their small subunit is linked to 21 proteins and has 1540 nucleotides.
  • A 5S RNA subunit (120 nucleotides) and a 23S RNA subunit make up the big subunit.
  • 31 proteins and a 2900 nucleotide RNA component.
  • Eukaryotes contain 80S ribosomes, which come in small (40S) and large (60S) component varieties.
  • One molecule of 18S ribosomal RNA (or rRNA), 30 proteins, and a prolate ellipsoid shape make up the smaller 40S ribosomal subunit (named as S1, S2, S3, and so on).
  • The bigger 60S ribosomal subunit is circular and has an escape route for polypeptide chains that are expanding.
  • It is made up of 40 proteins; 28S rRNA, 5.8 rRNA, and 5S rRNA; three different kinds of rRNA molecules (named as L1, L2, and so on).
  • Antibiotics that can eradicate bacterial infections without endangering human cells are made using the variations between bacterial and eukaryotic ribosomes.
  • The large and small subunits of the ribosomes found in the chloroplasts and mitochondria of eukaryotes are made of proteins and are housed within a 70S particle.
  • The ribosomes have a core structure that, despite variations in size, is the same for all ribosomes.
  • During protein synthesis, the two subunits join together and function as a single unit to convert the mRNA into a polypeptide chain.
  • They have a longer axis than they do in diameter because they are made up of two subunits that are not the same size.
  • When several ribosomes are connected to a similar mRNA strand during protein synthesis, a complex called a polysome is created.
  • The two subunits of ribosomes split after polypeptide synthesis and are reused or broken up, making ribosomes only exist momentarily.

Functions of Ribosomes

  • All live cells include the ribosome, a sophisticated molecular apparatus that is where biological protein synthesis takes place (translation).
  • Messenger RNA (mRNA) molecules dictate the order in which amino acids are linked together by ribosomes.
  • Peptidyl transfer and peptidyl hydrolysis are two crucial biological activities that ribosomes catalyse.


  • Verma, P. S., & Agrawal, V. K. (2006). Cell Biology, Genetics, Molecular Biology, Evolution & Ecology (1 ed.). S .Chand and company Ltd.
  • Alberts, B. (2004). Essential cell biology. New York, NY: Garland Science Pub.
  • Kar,D.K. and halder,S. (2015). Cell biology genetics and molecular biology.kolkata, New central book agency
  • https://biology.tutorvista.com/animal-and-plant-cells/ribosomes.html
  • https://alevelbiology.co.uk/notes/ribosomes-structure-and-functions/
  • https://biologywise.com/ribosomes-function
  • https://biologydictionary.net/ribosome/
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