GC: n

S: FAO – http://www.fao.org/docrep/W0073E/w0073e04.htm#P2096_237138 (last access: 2 January 2016); https://www.nlm.nih.gov/medlineplus/ency/article/002467.htm (last access: 2 January 2016).

N: 1. 1844, from French protéine, coined 1838 by Dutch chemist Gerhard Johan Mulder (1802-1880), perhaps on suggestion of Berzelius, from Greek proteios “the first quality,” from protos “first” + -ine.
Originally a theoretical substance thought to be essential to life, further studies of the substances he was working with overthrew this, but the words protein and proteid continued to be used in international work on the matter and also for other organic compounds; the modern use as a general name for a class of bodies arose in German. The confusion became so great a committee was set up in 1907 to sort out the nomenclature, which it did, giving protein its modern meaning and banishing proteid.
2. Like carbohydrates and fats, proteins contain carbon, hydrogen and oxygen, but they also contain nitrogen and often sulphur. They are particularly important as nitrogenous substances, and are necessary for growth and repair of the body. Proteins are the main structural constituents of the cells and tissues of the body, and they make up the greater portion of the substance of the muscles and organs (apart from water). The proteins in different body tissues are not all exactly the same. The proteins in liver, in blood and in specific hormones, for example, are all different.
Proteins are necessary

• for growth and development of the body;
• for body maintenance and the repair and replacement of worn out or damaged tissues;
• to produce metabolic and digestive enzymes;
• as an essential constituent of certain hormones, such as thyroxine and insulin.

Although proteins can yield energy, their main importance is rather as an essential constituent of all cells. All cells may need replacement from time to time, and their replacement requires protein.
Any protein eaten in excess of the amount needed for growth, cell and fluid replacement and various other metabolic functions is used to provide energy, which the body obtains by changing the protein into carbohydrate. If the carbohydrate and fat in the diet do not provide adequate energy, then protein is used to provide energy; as a result less protein is available for growth, cell replacement and other metabolic needs. This point is especially important for children, who need extra protein for growth. If they get too little food for their energy requirements, then the protein will be diverted for daily energy needs and will not be used for growth.

S: 1. OED – http://www.etymonline.com/index.php?term=protein (last access: 2 January 2016). 2. FAO – http://www.fao.org/docrep/W0073E/w0073e04.htm#P2096_237138 (last access: 2 January 2016).

SYN:
S:

CR: alanine, amino acid, enzyme, peptide, transferrin, translation (2), ubiquitin.