1	"Proteins" Proteins, from the Greek proteios, meaning first, are a class of organic compounds which are present in and vital to every living cell.
2	"In the form of skin" In the form of skin, hair, callus, cartilage, muscles, tendons and ligaments, Proteins hold together, protect, and provide structure to the body of a multicelled organism.
3	"In the form of enzymes" In the form of enzymes, hormones, antibodies, and globulins, they catalyze, regulate, and protect the body chemistry.
4	"In the form of hemoglobin" In the form of hemoglobin, myoglobin and various lipoproteins, they effect the transport of oxygen and other substances within an organism.
5	"Proteins are generally regarded as..." Proteins are generally regarded as beneficial, and are a necessary part of the diet of all animals.
6	"Humans can become seriously ill..." Humans can become seriously ill if they do not eat enough suitable protein, the disease kwashiorkor being an extreme form of protein deficiency.
7	"Protein based antibiotics and vaccines..." Protein based antibiotics and vaccines help to fight disease We warm and protect our bodies with clothing and shoes that are often protein in nature (e.g. wool, silk and leather).
8	"The deadly properties of protein..." The deadly properties of protein toxins and venoms is less widely appreciated. Botulinum toxin A, from Clostridium botulinum, is regarded as the most powerful poison known. Based on toxicology studies, a teaspoon of this toxin would be sufficient to kill a fifth of the world's population.
9	"The toxins produced by tetanus..." The toxins produced by tetanus and diphtheria microorganisms are nearly as poisonous. A list of highly toxic proteins or peptides would also include the venoms of many snakes, and ricin, the toxic protein found in castor beans.
10	"Despite the variety of their..." Despite the variety of their physiological function and differences in physical properties— silk is a flexible fiber, horn a tough rigid solid, the enzyme pepsin water soluble crystals Proteins are sufficiently similar in molecular structure to warrant treating them as a single chemical family.
11	"When compared with carbohydrates and..." When compared with carbohydrates and lipids, the proteins are obviously different in fundamental composition.
12	"The lipids are largely hydrocarbon..." The lipids are largely hydrocarbon in nature, generally being 75 to 85% carbon. Carbohydrates are roughly 50% oxygen, and like the lipids, usually have less than 5% nitrogen (often none at all).
13	"Proteins and peptides" Proteins and peptides, on the other hand, are composed of 15 to 25% nitrogen and about an equal amount of oxygen. The distinction between proteins and peptides is their size. Peptides are in a sense small proteins, having molecular weights less than 10,000.
14	Natural α-Amino Acids Hydrolysis of proteins by boiling aqueous acid or base yields an assortment of small molecules identified as α-aminocarboxylic acids.
15	More than twenty such components have been isolated, and the most common of these are listed in the following table.
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17	Those amino acids having green colored names are essential diet components, since they are not synthesized by human metabolic processes.
18	The best food source of these nutrients is protein, but it is important to recognize that not all proteins have equal nutritional value. For example, peanuts have a higher weight content of protein than fish or eggs, but the proportion of essential amino acids in peanut protein is only a third of that from the two other sources.
19	"Other Natural Amino Acids" Other Natural Amino Acids The twenty alpha-amino acids listed above are the primary components of proteins. Many other naturally occuring amino acids exist, and the structures of a few of these are listed below. Some, such as hydroxylysine and hydroxyproline, These two amino acids are found only in collagen, a common structural protein.