Ribosome
A ribosome is the particle upon which mRNA from DNA transcription is translated to a polypeptide with a specific amino acid sequence defined by the genetic code. It is comprised of 2 subunits:
30S unit: This is the smaller unit which consists of 21 proteins and a 16S RNA molecule
50S unit: This is the larger unit which consists of 34 proteins and 2 RNA molecules, 23S and 5S [1]
The 2 units together form the complete ribosome, known as the 70S unit. S refers to the Svedberg unit, which is a measure of rate at which a compound moves when centrifuged. It is used as a measure of size of a molecule but is not directly proportional to molecular weight [2].
As ribosomes contain RNA (also referred to as ribosomal RNA-rRNA) and proteins, they are also referred to as ribonucleoproteins. Ribosomes translate mRNA in triplets (codons) by alligning complementary triplets found in tRNA molecules (anticodons). Each tRNA is assigned a specific anticodon and amino acid and therefore translation leads to the formation of a protein by forming peptide bonds between adjacently aligned amino acids [3].
Ribosomes are small structures found in all living cells. They can be free in the cytoplasm or attached to endoplasmic reticulum (ER), making Rough ER. They can differ in size and number, according to whether they are found in bacteria, archaea or in eukaryotes. There are a large number of ribosomes in cells. In eukaryotes, there can be millions in one cell alone. As ribosomes are so small, (it has a diameter of 25-30 nm approximately) Becker, Wayne M., Kleinsmith, Lewis J., Hardin, Jeff., Bertoni, Gregory Paul. (2009) The World of the Cell, 7th Edition, San Francisco: Pearson Benjamin Cummings. P95., an electron microscope is needed to see it. Ribosomes are made up of two subunits, one larger than the other. The two subunits join together when attached to mRNA to make a protein in protein synthesis. Ribosomes are also found in mitochondria and chloroplasts and carry out protein synthesis, specifically for these organelles.