Protein Synthesis

Protein Synthesis

Before a protein molecule can be synthesized, the correct amino acids must be present in the cytoplasm to serve as building blocks Furthermore these amino acids must be positioned in the proper locations along a strand of messenger RNA . 

The positioning of amino acid molecules is the function of a second kind of RNA molecule called transfer RNA (tRNA). which consists of about KO nucleotide. Since 20 different kinds of amino acids are involved in protein synthesis, there must be at least 20 different kinds of transfer RNA molecules to serve as guides. However, before a transfer RNA molecule can pick up its particular kind of amino acid, the amino acid must be activated. 

In cell process 

This is a function of ATP, which provides the energy needed to form a bond between the amino acid and its transfer RNA molecule. Each type of transfer RNA includes a special region that contains 3 nucleotides in a particular sequence. These nucleotides can only bond to the complimentary set of 3 nucleotides of a messenger RNA molecule In this way . the transfer RNA carries its amino acid to a correct position on a messenger RNA strand. These actions occur on the surface of ribosomes. Each ribosome is a tiny particle of 2 unequalsized subuniis composed of rihosonuil RNA (rRNA) and protein. By its smaller subimit a ribosomc binds to a molecule of messenger RNA near a set of 3 nucleotides. This action allows a transfer RNA molecule with the complementary set of 3 nucleotides to recognize its correct location on the messenger RNA. 

The transfer RNA molecule brings the amino acid it carries into position and becomes temporary joined to the ribosome Then the transfer RNA molecule releases its amino acid and returns to the cytoplasm. This process is repeated again and again as the messenger RNA moves through the ribosome, and the amino acids, which are released by the transfer
RNA molecules, are added one at a time to a developing protein molecule. The enzymes necessary for the bonding of the amino acids are found in the larger sub unit of the ribosome. 

This sub unit also seems to hold the growing chain of amino acids as it develops. Actually, a molecule of messenger RNA is usually passing through several ribosomes at the same time. Thus, several protein molecules, each In a different stage of development, may be present at any given moment. As the protein molecule develops, it folds into its unique shape, and when it is completed it is released to become a separate functional molecule. The transfer RNA molecules can pick up other amino acids from the cytoplasm, and the messenger RNA molecules can function again and again.

Protein Synthesis 

ATP molecules provide the energy needed to form the various chemical bonds in this process. A complete protein molecule may consist of many hundreds of amino acids, and the energy from 3 ATP molecules is required to link each amino acid to the growing chain. Consequently, a large proportion of a cell's energy supply is needed to support
protein synthesis, especially if the cell is young and growing.