Ribosomes, first studied by
Palade, are some of the smallest structures suspended in the cytoplasm of a
cell and can only be seen under an electron microscope. They are roughly
spherical granular bodies that exist in two forms: (1) attached to the Rough
Endoplasmic Reticulum (RER) or (2) freely dispersed in the cytoplasm. Ribosomes
are composed of equal amounts of RNA and protein, making them
ribonucleoproteins.
In eukaryotes, all ribosomes
are made up of two subunits of different sizes, a larger one called the 60S
particle and a smaller one called the 40S particle. When these two subunits
attach to each other, they form an 80S particle. This attachment is controlled
by the presence of magnesium ions or the formation of salt bonds between the
phosphate group of RNA and the amino group of amino acids, or a combination of
both involving magnesium ions and salt bonds.
When several ribosomes are
attached to one mRNA strip, it is called a polysome, derived from
"poly" meaning many and "soma" meaning body.
Ribosomes are formed in the
nucleolus and then transported to the cytoplasm through the nuclear pores.
The main function of
ribosomes is to serve as the sites of protein synthesis, where the information
encoded in mRNA is used to synthesize proteins by linking amino acids together
in a specific sequence according to the genetic code.
No comments:
Post a Comment