Protein is one of essential macro molecule in our body made from amino acid polymers by peptide bond

1. CLASSIFICATION OF PROTEINS
• Proteins are classified into two major groups based on their
shape. As the name suggests, fibrous proteins are long, rod-
shaped molecules that are insoluble in water and physically
tough. Fibrous proteins, such as the keratins found in skin,
hair, and nails, have structural and protective functions.
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2. Cont.
• Globular proteins are compact spherical molecules that are
usually water- soluble. Typically, globular proteins have
dynamic functions. For example, nearly all enzymes have
globular structures. Other examples include the
immunoglobulins and the transport proteins hemoglobin and
albumin (a carrier of fatty acids in blood)
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3. Cont.
• On the basis of composition, proteins are classified as simple
or conjugated. Simple proteins, such as serum albumin and
keratin, contain only amino acids. In contrast, each
conjugated protein consists of a simple protein combined
with a nonprotein component.
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4. Cont.
• The nonprotein component is called a prosthetic group. (A
protein without its prosthetic group is called an apoprotein. A
protein molecule combined with its prosthetic group is
referred to as a holoprotein) Prosthetic groups typically play
an important, even crucial, role in the function of proteins.
Conjugated proteins are classified according to the nature of
their prosthetic groups
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5. Conjugated proteins
• Glycoproteins
• Mucoproteins
• Nucleoproteins
• Lipoproteins
• Metalloprotein
• Phosphoproteins
• Hemoproteins
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7. Functions of protein
• Catalysis
• Structure
• Regulation
• Contractile
• Movement
• Defense
• Transport
• Storage
• Stress response
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8. PROTEIN STRUCTURE
 Primary Structure : The sequence of amino acids in a protein
is called the primary structure of the protein.
 Understanding the primary structure of proteins is important
because many genetic diseases result in proteins with
abnormal amino acid sequences, which cause improper folding
and loss or impairment of normal function.
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9. Cont.
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10. SECONDARY STRUCTURE
• The polypeptide backbone does not assume a random three-
dimensional structure, but instead generally forms regular
arrangements of amino acids that are located near to each other
in the linear sequence. These arrangements are termed the
secondary structure of the polypeptide. The α-helix, β-sheet,
and β-bend (β-turn) are examples of secondary structures
frequently encountered in proteins.
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11. Cont.
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13. TERTIARY STRUCTURE
• Although globular proteins often contain significant numbers
of secondary structural elements, several other factors
contribute to their structure. The term tertiary structure refers
to the unique three-dimensional conformations that globular
proteins assume as they fold into their native (biologically
active) structures and prosthetic groups, if any, are inserted
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14. Cont.
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15. QUATERNARY STRUCTURE
• Many proteins, especially those with high molecular weights,
are composed of several polypeptide chains. As mentioned,
each polypeptide component is called a subunit. Subunits in a
protein complex may be identical or quite different.
Multisubunit proteins in which some or all subunits are
identical are referred to as oligomers
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17. Protein denaturation
• Considering the small differences in the free energy of folded
and unfolded proteins, it is not surprising that protein structure
is especially sensitive to environmental factors. Many physical
and chemical agents can disrupt a protein’s native
conformation
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18. Cont.
• The process of structure disruption, which may or may not
involve protein unfolding, is called denaturation.
(Denaturation is not usually considered to include the
breaking of peptide bonds.) Depending on the degree of
denaturation, the molecule may partially or completely lose its
biological activity
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19. Denaturing agents
• Strong acids or bases
• Heat
• Organic compounds
• Heavy metal ions
• Mechanical stress
• Detergents
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