Page 68 - Biology_F5

Cytology

protein and glycoprotein form the cell Biochemical test for proteins
surface membrane. Proteins are complex organic structures
made up of polypeptide chains of amino
(f) They take part in various metabolic acids, which have different amino
processes in the body. For example acid sequences and three dimensional
enzymes catalyse different configuration to define a particular type
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physiological activities in the body. of protein. An amino acid is a class of

(g) Proteins such as hormones act as organic compounds with a carboxyl
chemical messengers and regulate group (-COOH), an amino group (NH )
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body metabolites. Examples of such and a side group, all attached to a central
proteins are insulin and glucagon, carbon atom. Proteins differ from each
which regulate the level of blood other in terms of their type, number and
sugar in mammals. sequence of amino acids that make up
(h) Proteins, such as anti-bodies protect the polypeptide backbone. Therefore,
the body against infections. different proteins have different molecular
(i) Proteins, such as myosin and actin structures, nutritional attributes and
are contractile; therefore, they physico-chemical properties. There are
interact to bring about contraction several methods used to test for proteins.
and relaxation of muscles, hence, The most common method is chemical
bringing about movement of the body method. Chemical method relies on the
parts and locomotion of animals. properties of amino acids or peptide bonds
(j) Proteins, such as haemoglobin and that are common to all proteins. The biuret
myoglobin transport oxygen in the test is a chemical assay that is widely used
blood. to detect the presence of proteins and
(k) Proteins, such as fibrinogen are amino acids in a sample. The test relies
important for blood clotting, hence, on a color change to confirm the presence
they help in healing wounds by of proteins. If proteins are present, the
forming fibres over injured parts to sample will turn violet (Table 1.7).
prevent excessive loss of blood and
water, as well as entry of germs. The basis for protein tests
(l) Proteins such as ovalbumin of egg Biuret test is the chemical test used to
white and casein of milk are storage detect the presence of peptide bond as a
in function. For example, albumin general test for detection of proteins. In
supplies food to a developing embryo. the presence of dilute copper (II) sulphate
(m) Proteins help to build and improve (CuSO ) in alkaline solution (medium),
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the body immune system. This nitrogen atoms in the peptide chain form
explains why children suffering a purple complex with Copper (II) ions
2+
from kwashiorkor are vulnerable to (Cu ).
various opportunistic diseases.

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