Dipeptides, polypeptides and proteins:
Two amino acids joined together form a dipeptide. As more and more amino acids are joined together by peptide bonds, a polypeptide is formed.
A protein may consist of a single polypeptide chain of hundreds of amino acids. Some proteins consist of more than one polypeptide chain bonded to form and even larger molecule.
The amino acids in a polypeptide chain are sometimes referred to as amino acid residues, because part of the molecule is lost in the condensation reaction that produces a peptide bond.
Making polypeptides and proteins:
Polypeptides and proteins are made (synthesised) in cells on Ribosomes. This process is known as protein synthesis. It uses information in the form of a molecule called messenger RNA to put amino acids in the right order to make a specific polypeptide chain.
As the mRNA passes through the ribosome, amino acids are joined together one at a time. As each new amino acid joins, a condensation reaction occurs, forming a new peptide bond. This produces a longer and longer chain of amino acids. The sequence of amino acids produced is determined by the mRNA. To make different proteins, different mRNA molecules must pass through the Ribosomes.
An organism may contain 10 000 or so different proteins. Each protein has its own function within the organism. Each one is formed from amino acids joined by peptide bonds in a chain. A protein may be hundreds of amino acids long, but all proteins will have an amino group at the other.
The function of each protein is determined by its structure. The structure of each protein is determined firstly by it amino acid sequence. The unique amino acid sequence of a polypeptide or protein is called its primary structure.
Different amino acids have different properties.…