category: nutrition science: nutrients

Protein, de.: Eiweiß, Protein, fr.: protéines, it.: proteine, es.: proteína

Proteins contain, similar to carbohydrates and fat, the elements carbon (chem. symbol: C), hydrogen (chem. symbol: H) and oxygen (chem. symbol: O). They also contain nitrogen (chem. symbol: N) and some proteins sulphur (chem. symbol: S) or phosphorus (chem. symbol: P). These elements are combined to amino acids which are the essential components of all living: leucine, isoleucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.

In vegetables and fruits these amino acids can be found in high concentrations. Many people wrongly believe that vegetables do not supply us with enough proteins and the best protein source is meat. In contrast to meat vegetables have the advantage that they contain all essential amino acids.

Amino acids form long compounds that take a spiral form. Where proteins contain only amino acids they are called simple proteins. If other chemical components are added to the amino acid chains the proteins are called conjugated proteins and the added component prosthetic group. Examples of prosthetic groups are the iron in the haemoglobin of our blood and calcium in the caseinogen of milk.

Amino acid spirals fold up when they combine to proteins. Some develop into globelike shapes and are then called globular proteins or spheroproteins. Others form long strands and are called fibrous proteins. Albumin (contained in milk, eggs, fish, meat and potatoes), globulin (in meat, fish and pulses) and gluten (in cereals) are examples for globular proteins. One example of fibrous proteins are collagens that form the connective tissues of our body.

Three varieties of amino acids

Essential amino acids like isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine are essential for the composition of proteins in the body and cannot be synthesized. They therefore have to be supplied by our diet.

Conditionally essential amino acids like arginine, histidine, tyrosine and cystine/cysteine are not normally essential in our diet. In certain circumstances they may replace some essential amino acids though. Furthermore their supply in our diet may be necessary in some development stages or when a person suffers from certain diseases.

Non-essential amino acids like alanine, aspartic acid, aspartate, glutamic acid, glycine, serine and proline do not have to be supplied by out diet. The human body may synthesize them of other amino acids or other chemical compounds like keton acids.