RIBOSOMES

RIBOSOMES

Ribosomes are the sites of protein synthesis. All structural and functional proteins (enzymes) coded by the nuclear DNA, are synthesized upon cytoplasmic ribosomes. The DNA codes are transcripted into messenger RNA (mRNA) molecules in the chromosomes of the nucleus. mRNA molecules diffuse out  into the cytoplasm and each becomes attached to several ribosomes which thus from a group called polyribosome or polyribosomes. In this way each mRNA molecule brings about polymerization of specific protein molecules, with the help of ribosomes from amino acid molecules found in the Cytosol.

Ribosomes are responsible for assembling the proteins of the cell depending on the protein production level of a particular cell, ribosomes may number in the millions. Ribosomes are typically composed of two subunits, a large subunit and small subunit. These subunits are synthesized by the nucleolus.

                                                                       Fig: Ribosomes

Note :

• Ribosomes are spherical in shape and consist of two parts – In (80S; 60S and 40S) while in 70S (60S and 30S) are the subunits, in which 60S and 50S are the main subunits which are dome shaped while 40S and 30S are cap like structures.
• Eukaryotic ribosomes are 80S & 70S ribosomes.
• Universal cell organelles - Ribosomes.
• Ribosomes are the smallest cell organelles (230Å in diameter).
• Ribosomes were discovered and named by Palade (Hence called Palade granules).
• Membrane less cell organelles - Ribosomes.

Related Topics 

• Cell Wall
• Nucleus