Proteins contain the elements carbon, hydrogen, oxygen and nitrogen. They are made from long chains of amino acids. Amino acids have a carboxyl group (COOH) and amino group (NH2).
Glycine is the simplest structure of an amino acid.
Proteins and diet
Proteins can be found in eggs, milk, cheese, peanuts, meat and fish and is an important requirement for the growth and repair of tissues. There are 20 amino acids found in proteins and these can be divided into two groups:
- Non-essential amino-acids, (which are made by the liver)
- Essential amino acids, (which can not be made by the body and must be obtained from food)
Digestion of proteins
Protein digestion starts in the stomach. It produces the enzyme pepsin which breaks down proteins into polypeptides. These polypeptides are broken down further in the duodenum by the pancreatic enzymes trypsin, chymotrypsin and carboxypeptides into smaller polypeptides and amino acids. The amino acids are absorbed into the epithelial cells of the small intestine and transported to the liver.