The Building Blocks Of Proteins
The building blocks of proteins are amino acids. There are twenty different amino acids used by living cells to build proteins. They are linked together in a long, linear chain during the process of translation, which is carried out by the ribosomes inside cells. Proteins begin to take on their characteristic three-dimensional shape even while they are being made, folding and twisting as each new amino acid added to the chain tugs or pushes at the others added before it. Each amino acid has an amino group (-NH3+) and a carboxyl group (-COOH). Peptide bonds link the carboxyl group of one amino acid to the amino group of the next amino acid. On one end of a protein, therefore, there is a free amino group called the N-terminus, and on the other end is a free carboxyl group, called the C-terminus.
The process of determining a protein's order of amino acids is called protein sequencing. A protein's sequence can easily be deduced from its gene sequence, since the order of bases on a DNA strand specifies the order in which the amino acids are linked together during translation. The chemistry involved in DNA sequencing is less complex than that which is involved in determining the order of each amino acid in an amino acid chain. There are two primary reasons why effort would be put into sequencing a protein. The first is to provide the information needed to design a synthetic DNA probe that can be used to locate the gene that codes for the protein. The second is to prove that a protein that has been isolated or manufactured in the laboratory is what it is believed to be.