Vitamin c, the antiscorbutic vitamin

Vitamin C is water-soluble and is found chiefly in fresh fruits and vegetables, but its distribution is not very uniform. Lemon juice is very easily oxidized, particularly in alkaline solution. Lemon juice left exposed to the air loses all its vitamin C in three hours. It is readily destroyed by heat, but is sometimes present in canned or dried food if these are acid and have been preserved in the absence of air.

It has been synthesized from d-galactose, and exists in an oxi­dized and reduced form.

Most animals can manufacture it themselves, but they cannot make it in sufficient quantities and still need an outside supply for a healthy life.

The ease with which it is oxidized suggested that it acts at some point in tissue respiration and its absence leads to a break­down of protoplasmic structure. The chief deficiency disease, asso­ciated with it, is characterized by haemorrhage of the limbs and jaws. This is presumably caused by an increased permeability of the walls of the blood vessels.

Ascorbic acid is normally excreted in the urine, but in certain infectious diseases it is found there in smaller quantities than nor­mal, which suggests that it is being used up in the body. It has recently been shown that it inactivates diphtheria and vaccinia injected into rabbits. These facts say that its absence leads to a reduced resistance to infections. It is possible that it is used in the formation of antibodies.

Ex.11. Make up a short summary of text B out of the topical sentences. Use any of the following phrases:

1. The subject of the text is …

2. The author of the text says that …

3. He points out that …

4. Next the author emphasizes the idea that …

5. The author goes on saying that …

6. The text ends with …

7. The author concludes that …

Unit 13 Grammar: when, if + Participle II

Translate the following words and word combinations and remember them:

1. carbohydrate [‘ka:bou’haidreit]

2. polysaccharide [,poli’sækəraid]

3. starch [sta:t∫]

4. inulin [‘injulin]

5. cellulose [‘seljulous]

6. glucose [‘glu:kous]

7. fructose [‘frΛktous]

8. sucrose [‘sΛkrous]

9. to derive [di’raiv]

10. elimination [I,limi’nei∫n]

11. enormously [I’no:məsli]

12. sulphuric acid [sΛl’fjurik ‘æsid]

13. non-reducing [,nonri’dju:siŋ]

14. deoxy sugars [di’oksi ‘∫ugez]

15. explosive [iks’plousiv]

16. brewing [‘bru:iŋ]

17. to sweeten [swi:tn]

18. bitter taste [‘bitə’teist]

19. bloodstream [‘blΛdstri:m]

20. conventional practice [kən’ven∫ənl ‘præktis]

Carbohydrates

For years scientists have considered proteins the most essential constituent of all living tissues. Yet, there is another point of view today. As scientists learn more about other chemical constituents of living bodies, viz. carbohydrates and fats, they start speaking about the “three whales”, on which the life is based.

Carbohydrates are compounds containing the elements of carbon, hydrogen and oxygen, the last two elements being usually present¹ in the proportion, in which they are found in water (H₂O). The group includes sugars of different degrees of complexity and polysaccharides such as starch, inulin and cellulose.

Classification of carbohydrates:

1. Monosaccharides. These sugars contain three to nine carbon atoms, those with five and six carbon atoms (pentoses and hexoses) being the most important.

2. Di-, tri-, and tetra-saccharides. These sugars are theoretically derived from two, three or four monosaccharide molecules of water.

3. Polysaccharides. These are derived from sugar molecules by condensation with the elimination of water.

This group of compounds plays a vitally important part in the lives of plants, humans and animals, both as structural elements and one of the major sources of food. Cane and beet sugar, glucose, fructose, starch are typical representatives. Many of this group are of great commercial importance².

The properties of many carbohydrates differ enormously from one substance to another. The sugars, such as glucose and sucrose, are easily soluble, sweet-tasting and crystalline; the starches are colloidal and paste-forming, and the more complex cellulose is completely insoluble.

All carbohydrates give a violet colour when treated with alphanaphtol followed by concentrated sulphuric acid. Some carbohydrates are reducing. Non-reducing carbohydrates such as sucrose and the polysaccharides can be hydrolysed when boiled for about half an hour with a little dilute acid. The process of hydrolysis is a reversible one and more complex carbohydrates are synthesized in plants from sugar units. In addition to the sugars referred to above there are some relatively rare deoxy sugars, which have so far³ only been found in nature in cardiac glycosides. They include rhamnose, digitoxose, and cymarose.

Among the undertakings dependent on carbohydrate materials are the food industry, the cotton industry, certain branches of explosives, brewing, and the manufacture of alcohol. Of the group, glucose is the most widely used in pharmacy and medicine. When used as a constituent of a medicine, glucose sweetens its bitter taste making it more comfortable to be taken by patients. On the other hand, when a person is unable to take food in the normal way, he is fed through his bloodstream. Injections of glucose have long been conventional practice, as it is easily assimilated by the system to produce energy and strength.

Glucose can be made by boiling the potato or maize starch with acid. The starch combines with water and glucose is formed. When fermented, glucose gives ethyl alcohol, a substance with a vast number of uses in all branches including pharmacy and medicine.

Notes

1.the last two elements being usually present – при цьому, останні два елементи, звичайно присутні

2.commercial importance – промислове значення

3.so far – поки, що; до цього часу.