Учебно-методическое пособие по английскому языку для вузов. Кислякова Н.В - 15 стр.

                                      Proteins

   Proteins are the largest and the most complex molecules in the cell. They are
also nitrogenous organic substances of high molecular weight which form an
essential part of all living tissues. It is known that enzymes are proteins and all
the chemical processes involved in respiration metabolism are investigated and
controlled by enzyme activity. In living tissues, proteins are associated with
water and are present in colloidal state. Their individual behavior towards
environmental changes varies considerably.
  Proteins are classified chiefly according to their solubility; thus albumins are
soluble in water while globulins are insoluble in water but soluble in dilute salt
solutions. Both albumins and globulins are coagulated by heat. Hair and wool
consist of sclero-proteins which are characterized by their stability and
insolubility in water and salt solutions. All proteins are insoluble in organic
solvents and in alcohol. They are precipitated by the salts of heavy metals, by
the acids of high molecular weight. Another very sensitive test for proteins is
the formation of a film.
  Proteins have a great variety of structures and functions. The simple proteins
are composed of a large number of various amino-acids united together by
peptide bonds. They form molecules of colloidal dimension which may be
combined with other substances to form conjugated proteins. The main function
of proteins is to serve as a source of raw materials. The second function is to
provide cell energy.


Follow-up activities
IV. Agree or disagree with the following sentences:
1. Proteins are nitrogenous inorganic substances of low molecular weight.
2. They form an essential part of all living tissues.
3. All the chemical processes involved in respiration metabolism aren`t
investigated and controlled by enzyme activity.
4. Alkaloids are classified chiefly according to their solubility.
5. Sclero-proteins are characterized by their stability and insolubility in water.
6. A simpler function of proteins is to serve as a source of raw materials.


V. Read the text again and replace Russian words with their English equivalents
from the text.
1. Proteins are the largest and самые сложные молекулы in the cell.
2. Proteins are высокомолекулярны.
3. Proteins are present in колоидном состоянии.
4. Все протеины нерастворимы in organic solvents and in alcohol.
5. Amino-acids form molecules of коллоидного размера.
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