The document provides an extensive overview of proteins, covering their structures, functions, classifications, and the role of amino acids in protein synthesis. It explains the importance of proteins in bodily functions, their classification into simple, conjugated, and derived proteins, and highlights the consequences of protein malnutrition such as kwashiorkor and marasmus. Various tests for protein identification, as well as the properties of amino acids, are also discussed.

1. Prepared by
Shivanee Vyas
Assistant Professor
PROTEIN

2. INTRODUCTION to PROTEINS
Proteins are naturally occurring polymers made up of amino acids and linked
together by peptide bonds.
• Proteins are the most abundant organic molecules in the living system.
• The term protein is derived from the Greek word proteios, meaning holding the
first place.
• These are nitrogenous organic compounds that have large molecules weight of
one or more long chains of amino acids.
• Proteins are made from 20 ɑ-amino acids. (chains of amino acids)
• A single unit of amino acid is known as a monomer when many monomers
combine together they form polymers.
• On hydrolysis, proteins give amino acids.
• They are found in every cell in the body. They are involved in most of the body’s
functions and life processes.

3. Functions
of
PROTEINS
02

4. 1. They are responsible for the strength and structure of cells, tissue organs & body such
proteins are known as structural proteins. (e.g..- elastin & collagen)
2. The biochemical reactions taking place in the body are catalyzed by proteins called enzymes
(which participate in a chemical reaction and make the process fast).
3. Proteins are responsible for the transportation of metabolites known as transport proteins.
(also responsible for respiration)
4. Proteins that regulate metabolic pathways are known as regulatory proteins. (example:
insulin)
5. Proteins protect the body from infection and other toxins such proteins are known as defence
proteins. (Example: antibodies, immunoglobulins)
6. Some proteins are required for mechanical work and are known as muscle proteins.
7. The pH of various body fluids, osmotic pressure, temperature, & electrolyte balance is
regulated by various proteins.

5. CLASSIFICATION
OF
PROTEIN
03

6. Classification of Protein

7. 1. SIMPLE PROTEINS: They are composed of only amino acid residues.
A. Globular proteins: These are spherical or oval in shape, and soluble in water or other solvents.
i. Albumins and Globulins: These are globular proteins found in cells. e.g. serum albumin,
ovalbumin (egg), lactalbumin (milk), (egg yolk).
ii. Glutelins: Mostly found in plants e.g. glutelin (wheat), and oryzenin (rice).
iii. Prolamines: Soluble in 70% alcohol e.g. gliadin (wheat), zein (maize).
iv. Histones: These are basic proteins with higher molecular weight. They are heat coagulable.
Widely distributed in the body.
v. Globins: These are generally considered along with histones.
vi. Protamines: They are strongly basic and resemble histones but are smaller in size and soluble
in NH4OH. Protamine's are also found in association with nucleic acids e.g. sperm proteins.
vii. Lectins are carbohydrate-binding proteins and are involved in the interaction between cells
and proteins. They help to maintain tissue and organ structures. e.g., agglutinin

8. B. Fibrous proteins: These are fibre-like in shape, and insoluble in water.
i. Collagens They are connective tissue proteins and on boiling with water become
soluble and digestible.
ii. Elastins: These proteins are found in elastic tissues such as tendons and arteries.
iii. Keratins: These are proteins of skin, hair and nails.

9. 1. CONJUGATED PROTEIN: Besides the amino acids, these proteins contain a
non-protein moiety known as the prosthetic group or conjugating group.
i. Nucleoproteins: These are formed by the combination of histone with RNA or DNA.
ii. Chromo-proteins: These are soluble proteins combined with a chromophoric (coloured)
group. The coloured group is haem and riboflavin.
iii. Phosphoproteins Along with amino acid contain a phosphate group. Milk casein is an
example.
iv. Glycoproteins: Consists of amino sugars (carbohydrate and amino acids), sulphate and
sugar acids.
v. Lipoproteins: Combination of proteins with lipids found in the brain and membrane.
vi. Metalloprotein: Various metals (Fe, Co, Zn) are attached to simple proteins.

10. 3. DERIVED PROTEINS: These are the denatured or degraded products of
simple and conjugated proteins. The class are further subdivided into different
groups:
(a) Primary-derived proteins: The primary derived are the denatured or coagulated or first
hydrolyzed products of proteins.
i. Coagulated proteins: These are denatured proteins produced by heat, acids or alkalies.
Example: albumin (egg white)
ii. Proteans: These are the 1st or the earliest products of protein hydrolysis by enzymes,
dil. acids, alkalies. Example: fibrin from fibrinogen.
iii. Metaproteins: These are 2nd products of protein hydrolysis. In this stronger acids are
used. Example: acid and alkali metaproteins
(b) Secondary-derived proteins: The secondary derived are the degraded (due to the
breakdown of peptide bonds) products of proteins.

11. PROTEINS &
ITS
STRUCTURE

12. PROTEINS & ITS STRUCTURE
• Proteins are polymers of α-amino acids.
• Proteins have a complex structure and can be divided into four structures.
• The term protein is used for polypeptides containing more than 50 amino acids.
a) Primary structure: It is a linear structure of protein and forms the backbone of
proteins.
b) Secondary structure: It is the arrangement of protein structure in space (spatial
arrangement) by twisting the polypeptide chain.
c) Tertiary structure: It is the three-dimensional structure of proteins.
d) Quaternary structure: Composed of two or more polypeptide chains known as
subunits the spatial arrangements of these subunits is known as quaternary
structure.

14. PRIMARY STRUCTURE OF PROTEIN
• The primary structure of proteins is responsible for functions.
• Each protein has a unique sequence of amino acids linked together by peptide bonds.
• Abnormal amino acid sequencing causes various illnesses.
• Peptide bonds form when amino and carboxyl groups of two amino acids interact.

15. • The secondary structure is the shape of the polypeptide chain through twisting and folding.
• There are two types of secondary structures:
1. ɑ-helix (alfa-helix)
2. β-sheet (beta-sheet)
SECONDARY STRUCTURE OF PROTEIN
1. Alfa-helix
• It is the most common spiral
structure of the protein in which
the amino acids are tightly
packed and coiled.
• The formation of alfa-helix
requires the lowest energy.

16. 2. Beta-sheet or beta-pleated sheet
• In this, hydrogen bonds are formed between the
neighbouring segments of polypeptides.
• The peptide is held together giving a sheet-like
structure.
• Can be parallel (same direction) or antiparallel
(opposite direction).

17. • It is the three-dimensional arrangement of protein structure.
• In this, the hydrophobic side chain is held inside and hydrophilic groups are held outside
(surface).
• The above arrangement gives stability to the molecule.
• The interactions include:
 Hydrogen bonds
 Hydrophobic bonds
 Ionic bonds
 Di-sulphide bonds
TERTIARY STRUCTURE OF PROTEINS

18. • Some proteins contain 2 or more polypeptides held together by non-covalent bonds.
• These 2 polypeptide chains are called oligomers and a single polypeptide is called a
monomer.
• Haemoglobin has 4 polypeptides.
• Bonds can be hydrogen, ionic or hydrophobic.
QUATERNARY STRUCTURE OF PROTEINS

19. PROPERTIES
OF
PROTEINS

20. PROPERTIES OF PROTEINS
• Solubility: Proteins have huge sizes and therefore form a colloidal solution in water.
• Molecular weight: The molecular weight of proteins varies depending on the number of amino
acids. They have high molecular weight. The molecular weight ranges from 40-40,000.
• Shape: Their shape varies. Insulin has a globular shape, albumin has an oval shape, and
fibrinogen has an elongated shape.
• Zwitterion: An ion carrying both a positive and a negative charge in different parts of the
molecule.
• Precipitation: proteins get dehydrated when salts such as ammonium sulfate are added.
Dehydration also results from the addition of salts of heavy metals like Pb2+, Zn2+ etc. Alcohol
also dehydrates protein. Tannic acid and picric acid also dehydrate protein. Dehydration of
protein results in the precipitation of proteins.
• Coagulation: It is a semisolid or solid precipitate of protein that is irreversible. Example:
albumin.

21. AMINO ACID
04

22. • Amino acids are a group of organic compounds containing two functional groups:
a) Amino (-NH2)
b) Carboxyl (-COOH)
• These functional groups are attached to Alfa-carbon and therefore are called ɑ-amino acids.
• There are more than 300 amino acids in nature but out of these only 20 are known as
standard amino acids.
• In the structure given below R represents a side chain attached to α carbon and each of the 20
amino acids has a different R group or side chain i.e. all the amino acids differ in the structure
of the side chain.
AMINO ACIDS

23. AMINO ACID
Based on
structure
Based on
polarity
Nutritional
classification
1. Aliphatic amino acid
2. Aromatic amino acid
3. Amino acid-
containing hydroxyl
group
4. Sulfur containing
amino acid
5. Acidic amino acid
6. Basic amino acid
7. Imino acids
1. Non-polar amino
acid
2. Polar amino acid
1. Essential amino
acid
2. Non-essential
amino acid

24. 1. Aliphatic amino acids: e.g., alanine, glycine, valine, leucine, isoleucine.
2. Aromatic amino acids: e.g. phenylalanine, tyrosine, tryptophan.
1. STRUCTURAL CLASSIFICATION OF AMINO ACID
valine

25. 3. Hydroxyl group-containing amino acids: serine, threonine
4. Sulphur containing amino acids: e.g. cysteine, methionine.

26. 5. Acidic amino acids: e.g. glutamic acid, aspartic acid.
6. Basic amino acids: e.g. histidine, lysine, arginine.

27. 7. Imino acids: e.g. proline.
proline

28. 2. CLASSIFICATION OF AMINO ACIDS BASED ON POLARITY
1. Nonpolar amino acids: These amino acids are also known as hydrophobic or water-
hating. They have no charge on the R group. Examples: alanine, valine, and leucine.
2. Polar amino acids: These amino acids are also known as hydrophilic or water-loving.
They have a charge on the R group. Examples: glycine, serine, cysteine.
3. CLASSIFICATION OF AMINO ACID – ESSENTIAL AND NON
ESSENTIAL
1. Essential amino acids: These amino acids cannot be synthesized in the body and
therefore be supplied through the diet. It is required for proper growth and maintenance.
Examples: Valine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine,
tryptophan, Arginine, and histidine.
2. Nonessential amino acids: These amino acids are synthesized in the body. They need
not be consumed in the diet. The body can synthesize 10 amino acids. Examples: glycine,
alanine, serine, cysteine, aspartate, asparagine, glutamate, glutamine, tyrosine, proline

29. 1. Physical properties: Colourless, and crystalline.
2. Solubility: All amino acids are soluble in water but the extent to which they are soluble
varies. R group determines the solubility. Polar amino acids are highly soluble in water.
Nonpolar amino acids are soluble in organic solvents (chloroform).
3. Melting point: As they are high molecular weight compounds they have higher melting
points. Mostly above 200°C.
4. Taste: Amino acids can be sweet (glycine), bitter (arginine) or tasteless (leucine)
5. Optical activity: All amino acids except glycine are optically active.
PROPERTIES OF AMINO ACIDS

30. 1. Build Protein: When cells need protein, they follow instructions from DNA that
define the specific amino acids and the order in which they must connect to build
the protein.
2. Synthesize Neurotransmitters: Several amino acids produce
neurotransmitters like GABA
3. Protect Cardiovascular Health: the body uses the amino acid arginine to make
nitric oxide. Nitric oxide helps lower blood pressure by relaxing muscles in your
blood vessels.
Functions of Amino Acid

31. 1. Heat test: When protein solution is heated in a boiling water bath, it gets coagulated and loses
their biological activity. This is called the denaturation of protein. As heat causes denaturation, it
is called thermal denaturation.
2. Test with trichloroacetic acid (TCA): TCA is used to precipitate proteins from their solution.
Due to the addition of acid, proteins get denatured.
3. Biuret test: Biuret reagent contains copper sulphate in an alkaline solution. Also contains
sodium Potassium tartrate. Proteins reduce the cu2+ ions to cu+ ions. When proteins are treated
with biuret regent it gives a violet colour. This test is used for the identification of proteins.
4. Hydrolysis test: Proteins on hydrolysis give amino acids. Hydrolysis can be carried out by acids
like hydrochloric acid, and conc. Sulphuric acid etc.
5. Xanthoproteic reaction: Same as amino acids. Nitration of aromatic amino acids will give
yellow colour which in addition to alkali turns orange.
6. Millons test: Proteins react with mercuric sulphate in presence of sodium nitrite and sulphuric
acid to give red colour.
REACTIONS OF PROTEINS

32. A deficiency of protein from early childhood is regarded as a
disease.
1. Kwashiorkor is a severe protein malnutrition disease.
Appears at the age of 1-4 years.
• Symptoms: Retarted growth, Edema (excess water in the body
tissues which results in swelling of the body), Alterations in the
skin. (patches or redness on the skin) Hair pigmentation and
texture changes. (which means the colour of the skin becomes
dark or changes), Liver enlargement Vomiting and diarrhoea
and stools contain undigested food.
• Causes: Poor maternal (mothers) health, Large family size
Termination, or delayed breastfeeding. Environmental
conditions. Over diluted cow’s milk.
• Cure: Diet rich in protein such as milk and eggs. Soya beans
are the best vegetable source of protein.
DISORDERS OF PROTEIN DEFICIENCY

33. 2. Marasmus: This disease is the same as kwashiorkor but
occurs before in infants i.e. below 1 year of age.
• Causes: Due to nutritional deficiency in carbohydrates, proteins,
etc. Stoppage of early breastfeeding is the most important
cause.
• Cure: Providing a diet rich in proteins.
3. Nutritional oedema: It is a swelling caused due to
insufficient protein intake.
• Causes: Long continuous deprivation of proteins in the diet. This
deficiency in adults is rare.
• Symptoms in adults: Loss of weight, Anemia, Constant
infection, Frequent loose stools, and Delay in healing wounds.
• Cure: Diet rich in proteins, Soyabean, milk and eggs in the diet.

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