Unit 2.1 - Topic 7

Proteins from amino acids.

Dipeptides, polypeptides and proteins.

Two amino acids joined together form a dipeptide. As more and more amino acids join together by peptide bonds, a polypeptide is formed.

A protein may consist of one polypeptide chain of hundreds of amino acids. However, some proteins consist of more than one polypeptide chain bonded to form an 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 the 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 ( mRNA) 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 chain of amino acids. The sequence amino acids produced is determined by the mRNA. To…