Proteins are made up of amino acids and play many critical roles in the body. They have a primary structure formed by a linear chain of amino acids and can fold into secondary and tertiary structures. Proteins are classified based on their composition, structure, and function. They serve as enzymes, structural components, nutrients, regulators, defense agents, transporters, and storage molecules essential for growth, repair, movement, signaling, immunity, and all biochemical reactions in the body.

1. PROTEINS
Mrs.A.JEEVARATHINAM
ASSISTANT PROFESSOR
DEPARTMENT OF HOME SCIENCE
V.V.VANNIAPERUMAL COLLEGE FOR WOMEN
VIRUDHUNAGAR

2. INTRODUCTION
• Protein is one of three macronutrients, which are
nutrients the body needs in larger amounts.
• Proteins are large, complex molecules that play
many critical roles in the body.
• It is a part of every cell in the body.
• They are made up of hundreds or thousands of
smaller units called amino acids, which are
attached to one another in long chains.
• Proteins are the essential building blocks of our
body and the vital nutrients in our diet.

3. STRUCTURE OF PROTEINS
• Protein is made up of amino acids. Each amino
acid is an organic molecule consisting of a
central carbon atom attached to an amino
group, carboxyl group, hydrogen atom and a
variable side chain (R group). There are 20
amino acids common to most proteins and
fewer common ones.

4. STRUCTURE OF PROTEINS
• Each amino acid is linked with the next one
through a covalent bond called a peptide
bond. Many such amino acids join to form a
linear chain. This linear chain is called
a polypeptide. Biologically occurring
polypeptides vary in size and consist of two to
three thousand amino acids. The linear chain
of amino acids, i.e., polypeptide, becomes
the primary structure. It may consist of one or
many polypeptides.

5. STRUCTURE OF PROTEINS
• When the amino acids join, the side chains or R
groups acquire a particular spatial arrangement,
called conformation. Such conformations decide
the secondary and tertiary structures. Due to
intermolecular attractions between the R groups,
the polypeptide chains fold onto themselves in
characteristic ways. The foldings form two
patterns called α–helix and β–sheets.
These stable foldings make the secondary
structures of a protein. The three-dimensional
arrangement of helices and sheets makes the
tertiary structure.

6. PROTEIN STRUCTURE

7. SOURCES OF PROTEIN
The guidelines classify the following foods as protein foods:
• seafood
• lean meats and poultry
• eggs
• legumes, which include beans and peas
• nuts
• seeds
• soy products
• Dairy products, such as milk, cheese, and yogurt, also
contain protein. Whole grains and vegetables contain some
protein, but generally less than other sources.

8. FUNCTIONS OF PROTEINS
• Proteins are required for the growth and repair of body tissues.All our body muscles are
made up of proteins.
• Roughly 30 per cent of our body is muscles.
• Proteins provide the essential structure to the body.
• They provide elasticity, rigidity, and shape to many internal and external organs.
• All enzymes in our body are made up of proteins. So, all biochemical reactions in the body
are carried by proteins.
• Every cell has a membrane composed of different proteins essential for all vital functions.
• Many messengers of the body, i.e., hormones, are proteins. Thus, they act as messengers
too.
• Proteins contribute to our blood in a greater way:
a. 6−8 per cent of blood plasma is proteins.
b. The Hemoglobin of RBCs is protein.
c. Many proteins present in the blood plasma like albumin, globulin maintain the osmotic
pressure and pH of the blood and thus keep the body fluids of the entire body.
d. Proteins boost our immunity by making up the immunoglobulins (antibodies) and
complement proteins in our blood.
e. They help in blood clotting.
• It transports different types of substances across the body through blood
• Proteins also provide the energy required by our body for various functions.

9. CLASSIFICATION OF PROTEINS
• Proteins can be classified based on
i)composition
ii)structure
iii)function.

10. BASED ON COMPOSITION
• Simple proteins are made up of amino acids only, and no other
chemical group is attached to them. Their structures are relatively
simple. Few examples are albumin, globulin, histones, protamines,
etc.
• Complex or Conjugate proteins have the non-protein moiety
(prosthetic group) attached to them to become functional. Thus,
they have both protein and non-protein components in them.
Based on the nature of the prosthetic group, attached proteins can
further be classified as
:
a. Metalloproteins: Prosthetic group is a metal ion and essential for
the functioning of the protein. Examples: Cytochrome c oxidase,
peroxidase, nitrate reductase, urease, carbonic anhydrase etc.
b. Chromoproteins: When the prosthetic group is a pigment or
chrome (colouring substance), protein is called chromoprotein.
Examples: Haemoglobin (Fe gives red colour) and chlorophyll
(tetrapyrrole rings give the green colour).

11. BASED ON COMPOSITION
• c. Glycoproteins: Also known as mucoproteins, these have
carbohydrates as a prosthetic group. Examples: Antibodies,
Heparin, Hyaluronic acid.
• d. Lipoproteins: The prosthetic group of these proteins is
lipid. Examples: Lipovitelline, chylomicrons, etc.
e. Phosphoproteins: The prosthetic group is a phosphate
molecule. Examples: Casein (milk protein) and ovo-vitelline
(egg yolk protein).
f. Nucleoproteins: Here, the prosthetic group is a nucleic acid.
Examples: Proteins in chromosomes and ribosomes.
g. Flavoproteins: The prosthetic group is FAD (Flavin Adenine
Dinucleotide). Examples are proteins of the electron transport
chain.
• Derived proteins are those which are either derived from
simple proteins or complex proteins. Heat, enzyme action or
chemical actions may produce derived proteins. Examples:
Proteins, peptides, and some artificially produced proteins.

12. BASED ON STRUCTURE
Based on the structure, proteins can be classified as:
• Fibrous Proteins have long fibre-like structures. Their
length to breadth ratio (axial ratio) is more than 10. Fibrous
proteins have more structural roles.
Examples: Keratin, collagen, elastin, fibroin, etc.
• Globular Proteins have spherical or rounded structures, as
their name suggests, and their axial ratio is always less than
10. Globular proteins have more functional roles.
Examples: Albumin, globulin, histones, etc.
• Intermediate Proteins have their structure intermediate
between fibrous and globular proteins. They are short and
more or less linear-shaped. An example is a fibrinogen.

13. BASED ON FUNCTIONS
• Catalytic Proteins: These carry out all biochemical and catalytic functions and a
typical example includes all enzymes and coenzymes.
• Structural Proteins: These make up the structural components of connective
tissue, bones, cartilage, tendons, ligaments, skin, hair, feathers, nails and horns.
Example: Collagen, elastin, keratin, etc.
• Nutrient Proteins: These have nutritional values and provide nutrition.
Example: Albumin, casein, etc.
• Regulatory Proteins: These regulate metabolic and cellular activities in the body.
Examples: Hormones, cell signaling molecules and membrane proteins.
• Defense Proteins: These provide immunity to the body against pathogens.
Example: Antibodies and complement proteins
• Transport Proteins: Helps transport various substances across the body. They
transport nutrients, vitamins and even respiratory gases like oxygen and carbon
dioxide. Haemoglobin is a classic example of transport protein that transports
oxygen to every cell of the body. Other examples include globulins, albumin, etc.
• Storage Proteins: They act as a storehouse of many ions and molecules.
Example: Ferritin (which stores ions), albumin, etc.