The discovery dates of the vitamins and their sources
Year of discovery Vitamin Food source 1913 Vitamin А (Retinol) Cod liver oil 1910 Vitamin В1(Thiamine) Rice bran 1920 Vitamin С (Ascorbic acid) Citrus, most fresh foods 1920 Vitamin D (Calciferol) Cod liver oil 1920 Vitamin В2(Riboflavin) Meat, eggs 1922 Vitamin Е (Tocopherol) Wheat germ oil, unrefined vegetable oils 1926 Vitamin В12(Cobalamins) liver, eggs, animal products 1929 Vitamin К1(Phylloquinone) Leafy green vegetables 1931 Vitamin В5 (Pantothenic) Meat, whole grains, in many foods 1931 Vitamin В7(Biotin) Meat, dairy products, eggs 1934 Vitamin В6 (Pyridoxine) Meat, dairy products 1936 Vitamin В3(Niacin) Meat, eggs, grains 1941 Vitamin В9 (Folic acid) Leafy green vegetables

Vitamins are classified according to their biological and chemical activity, but not to their structure. Vitamins have diverse biochemical functions. Some have hormone-like functions as regulators of mineral metabolism (e.g., vitamin D), or regulators of cell and tissue growth and differentiation (e.g., some forms of vitamin A). Others function as antioxidants (e.g., vitamin E and sometimes vitamin C). The largest number of vitamins (e.g., B complex vitamins) function as precursors for enzyme cofactors, that help enzymes in their work as catalysts in metabolism. Vitamins may also be less tightly bound to enzyme catalysts as coenzymes, detachable molecules that function to carry chemical groups or electrons between molecules. For example, folic acid carries various forms of carbon group–methyl, formyl, and methylene– in the cell. Although these roles in assisting enzyme-substrate reactions are vitamins’ best-known function, the other vitamin functions are equally important.

The term vitamin was derived from “vitamine”, a combination word made up by Polish scientist Casimir Funk from vital and amine, meaning amine of life, because it was suggested in 1912 that the organic micronutrient food factors that prevent beriberi and perhaps other similar dietary-deficiency diseases might be chemical amines. This proved incorrect for the micronutrient class, and the word was shortened to vitamin.

Vitamins are classified as either water-soluble or fat-soluble. There are 13 vitaminsin humans: 4 fat-soluble (A, D, E and K) and 9 water-soluble (8 B vitamins and vitamin C). Water-soluble vitamins are dissolved easily in water and, in general, are readily excreted from the body. Fat-soluble vitamins are absorbed through the intestinal tract with the help of lipids (fats).

Vitamins are essential for the normal growth and development of a multicellular organism. Humans must consume vitamins periodically but with differing schedules, to avoid deficiency. Being overdosed, some vitamins cause side-effects such as nausea, diarrhea, and vomiting.

 

Task 1. Learn the following words and word combinations

amount [ə'maunt] количество
catalyst ['kæt(ə)lɪst] катализатор
cell [sel] клетка
compound ['kɔmpaund] смесь, соединение, составной
consume [kən'sju:m] потреблять
deficiency [dɪ'fɪʃ(ə)nsɪ] недостаток, недостаточность, дефицит
development [dɪ'veləpmənt] развитие
diverse [daɪ'vɜːs] разнообразный
enzyme ['enzaɪm] фермент
essential [ɪ'senʃ(ə)l] существенный, важный, необходимый, основной
growth [grəuθ] рост
intestinal tract [ɪn'testɪn(ə)l][trækt] желудочно-кишечный тракт
multicellular [mʌltɪsɛljʊlə] многоклеточный
nutrient ['nju:trɪənt] питательное вещество
obtain [əb'teɪn] получать
precursor [prɪ'kɜːsə] клетка- предшественник
prevent [prɪ'vent] предотвращать
quantity ['kwɔntətɪ] количество
require [rɪ'kwaɪə] требовать(ч.-л)
scientist ['saɪəntɪst] ученый
side-effect [saɪd][ɪ'fekt] побочное действие
tissue ['tɪʃu:] ткань

Дата: 2018-12-28, просмотров: 43.