Page 62 - Biology_F5

Cytology

Intermediate proteins: These are fibrous, Simple proteins: These are proteins made
soluble proteins. A typical example of up of only amino acids, and are mostly
intermediate proteins is fibrinogen, which globular. When decomposed by acids,
forms an insoluble fibrin during blood these proteins liberate their constituent
clotting. amino acids. Examples of simple proteins
are albumins, globulins, and histones.
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(b) Classification of proteins based on
their composition Conjugated proteins: These are proteins
Based on their composition, proteins can made up of amino acids and other organic
compounds. They have a non-amino
be classified as simple and conjugated or acid group termed as prosthetic group.
complex proteins. Examples of conjugated proteins and their
prosthetic groups are shown in Table 1.6.

Table 1.6: Conjugated proteins: their prosthetic groups, and locations

Name Prosthetic group Location

Phosphoprotein Phosphoric acid Casein of milk and vitelline of egg yolk

Glycoprotein Carbohydrate Cell membrane, and mucin (component of
saliva)

Nucleoprotein Nucleic acid Component in the structures
of viruses, chromosomes and
ribosomes

Lipoprotein Lipid Cell membrane and lipids transported in
blood as lipoprotein

(c) Classification of proteins based on the polypeptide chain (Figure 1.37). Its
their level of organisation sequence is determined by the sequence of
There are four types of proteins based nucleotide bases of the DNA in the genetic
on the level of structural organisation, code. The amino acid sequence determines
namely primary, secondary, tertiary, and
quaternary structures of proteins. the positioning of different R-groups
relative to each other. The positioning also

Primary structure of proteins: The determines the way the protein folds and
primary structure of protein is a linear the final structure of the molecule.
sequence of amino acids that make up

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