Summary Proteins and amino acids

Proteins

 All enzymes are proteins
 Essential components of cell membrane – functions such as receptor
proteins and signally proteins
 Hormones – insulin and glycogen
 Oxygen carrying pigment in haemoglobin
 Antibodies
 Collagen – adds strength to animal tissues such as bones and walls of
arteries
 Keratin – hair, nails and surface layer of the skin
 Actin and myosin for muscle contraction
 Can be storage products

Amino acids

 Simplest amino acid is glycine
 All have a central carbon bonded to amine group –NH2, and a carboxyl
acid group –COOH
 3rd component - hydrogen always bonded
to the carbon atom
 20 different amino acids – all with
different R groups

Peptide bonds: 2 amino acids can join together,
1 loses a hydroxyl group –OH and the other
loses a H atom. Therefore the carbon can bond
with the nitrogen forming a peptide bond. The
remaining H2 and O form water.

The new molecule that has been formed is
called a dipeptide. A molecule made of many
amino acids is called a polypeptide. A complete
protein may have one
H2O polypeptide chain or
many more.


In cells, ribosomes are where amino acids are joined to make polypeptides and
the reaction is controlled by enzymes.

By hydrolysis (addition of water), the polypeptides can be broken down into
amino acids, by breaking the peptide bonds. This happens in the small
intestine and stomach during digestion so protein molecules can be
hydrolysed into amino acids to be absorbed.