Переведите письменно текст. protein (complete, partially complete, incomplete); to vary variation; to link, to maintain, maintenance

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protein (complete, partially complete, incomplete); to vary variation; to link, to maintain, maintenance, to value, value, valuable; to support; to classify; to result in; to base upon; adequate; to be able, ability.

«PROTEINS»

Proteins differ from carbohydrates in that, besides the elements present in sugar and starches, they also contain nitrogen and in most cases sulphur. Phosphorus and iron are also found in some proteins. The importance of nitrogen content commonly varies from 10 to 18 per cent. Proteins are found in foods of both animal and plant origin. Meat, eggs, milk, nuts and certain of cereal foods are high in protein. All those foods contain more than one protein. Milk, for example, contains the proteins, lactalbumin and casein, as well as others of lesser importance.

Proteins are complex in nature, they are composed of a number of amino acids or “building blocks”, linked together, and also of amino acids linked with other substances. Proteins vary in the kind and number of amino acids present. Certain amino acids the body is unable to build. These are known as essential amino acids and must be supplied by the foods eaten.

Variation in the quality of proteins has resulted in their classification as complete, partially complete, and incomplete, based upon their ability to support normal growth and to maintain life even if it is the only protein in the diet. A partially complete protein is one that maintain life but does not support normal growth. An incomplete protein, although valuable in the diet, will by itself neither support normal growth nor maintain life. Most animal proteins are complete. Plant proteins are more or less incomplete, although the soya bean and the wheat grain contain proteins that are complete. Valuable sources of protein are: cereals and cereal products, cheese, eggs, fish, meat, milk, nuts.

Ответьте письменно на вопросы.

1. What is the composition of proteins? 2. What foods are valuable sources of proteins? 3. What is the basis of protein classification?