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Protein

Here you can learn all about proteins and follow links to main sources of protein in our natural diet, all here at itscooking.com.

Protein in food consists of a large number of organic compounds consisting of amino acids linked together by peptide bonds; these make up living organisms and are essential to their functioning. Proteins were first discovered in 1838 and are now recognized as the predominant ingredients of cells, making up more than 50 per cent of the dry weight of animals. The word protein is coined from the Greek proteios, or “primary.”

Protein molecules range from the long, insoluble fibres that make up connective tissue and hair to the compact, soluble globules that can pass through cell membranes and set off metabolic reactions. They are all large molecules, ranging in molecular weight from a few thousand to more than a million, and are specific for each species and for each organ of each species. Humans have an estimated 30,000 different proteins, of which only about 2 per cent have been adequately described. Proteins in the diet serve primarily to build and maintain cells, but their chemical breakdown also provides energy, yielding close to the same 4 calories per gram as do carbohydrates (see Metabolism).

Besides their function in growth and cell maintenance, proteins are also responsible for muscle contraction. The digestive enzymes are proteins, as are insulin and most other hormones, the antibodies of the immune system, and haemoglobin, which carries vital substances throughout the body. Chromosomes, which transmit all hereditary characteristics in the form of genes, are composed of nucleic acids and proteins.

 

Nutritional effects of Protein

Whether found in humans or in single-celled bacteria, proteins are composed of units of about 20 different amino acids, which, in turn, are composed of carbon, hydrogen, oxygen, nitrogen, and sometimes sulphur. In a protein molecule these acids form peptide bonds; bonds between amino and carboxyl (COOH) groups—in long strands (polypeptide chains). The almost numberless combinations in which the acids line up, and the helical and globular shapes into which the strands coil, help to explain the great diversity of tasks that proteins perform in living matter.

The primary structure of a protein is its amino acid sequence, formed when a peptide bond joins the carboxyl group (one Carbon atom, two Oxygen atoms, and a Hydrogen atom) of one amino acid to the amino group (N) of another. A long chain forms from many amino acids, with one molecule of water given off with the formation of each peptide “link”.

To synthesize its life-essential proteins, each species needs given proportions of the 20 main amino acids. Although plants can manufacture all their amino acids from nitrogen, carbon dioxide, and other chemicals through photosynthesis, most other organisms can manufacture only some of them. The remaining ones, called essential amino acids, must be derived from food. Eight essential amino acids are needed to maintain health in humans: leucine, isoleucine, lysine, methionine, phenylalanine, theonine, tryptophan, and valine. All of these are available in proteins produced in the seeds of plants, but because plant sources are often weak in lysine and tryptophan, nutrition experts advise supplementing the diet with animal protein from Meat, eggs, and milk, which contain all the essential acids.

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