No living organisms are stable. They
are in a continual state of chemical change. All the time that we are alive we
are continually dying and being reborn. About three million of our blood
cell die while we read a sentence, and at the same time three million more
cells are made.
word metabolism is used to signify the chemical changes which take place in
living organisms. By using of suitable measuring instruments it is possible to
follow the blood cells in the body and to find out how long they live. This
work has revealed that the average life of each blood cell is about a
fortnight. Even bones are much less stable than we might expect. It is clear
that since the living body is in a state of constant change, the chemical
changes must be precisely controlled.
now know that each of the many thousands of chemical reactions which take place
in a living body is controlled by a particular enzyme. Enzymes are organic
catalysts which take part in the chemical processes occurring in living bodies.
The change of one form of sugar into another, a reaction which is common in
living organisms, is a simple instance of the action of an enzyme. This means
that in the presence of water a molecule of sucrose may split into two smaller
molecules, one of glucose and the other of fructose. These are sugars which
each have the same molecular formula but the atoms are arranged differently in
great number of enzymes bring about hydrolysis - that is a chemical reaction in
the presence of water. The process of digestion is brought about by hydrolyzing
enzymes. Another group of enzymes brings about oxidation’s. i.e. reaction
during which pairs of hydrogen atoms are removed from molecules and are
combined with oxygen atoms to make water. It seems probable that a single cell
may contain a thousand or more different enzymes which bring about a similar
number of chemical reactions.
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