The document discusses proteins and amino acids, emphasizing their structure, classification, and biological roles. It outlines the importance of proteins in various functions such as digestion, hormonal regulation, and defense, as well as the consequences of protein malnutrition, including diseases like kwashiorkor and marasmus. Various qualitative tests for proteins are also described, such as the biuret and xanthoproteic tests.

1. Proteins and Amino Acids
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By
Sukanta Debnath
Asst. Professor
Dept, of Pharmacy
Mata Gujri University

2. Introduction
 Proteins are large biomolecules and macromolecules that
consist one or more long chains of amino acid residues.
 A linear chain of amino acid residues is called
a polypeptide.
 Proteins contain carbon, hydrogen, oxygen, nitrogen, and
sulphur.
 Proteins are highly complex molecules that are actively
involved in the most basic and important aspects of life
like metabolism, movement, defence, cellular
communication.
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3. Structure of Protein
A peptide has two ends: the end with
a free amino group is called the N-
terminal amino acid residue. The end
with a free carboxyl group is called the
C-terminal amino acid residue.
Peptides are named from the N-
terminal acid residue to the C-terminal
amino acid.
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4. Classification based on composition
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Amino Acids
 These are organic compounds that have both group amino (-NH2) and
Carboxylic group (-COOH)
 At least 500 amino acids are there in nature
 They are the building blocks of proteins
 It derived from –NH2 and –COOH group that why its called amino acid.

6. Classification of amino acids based on Chemical composition
Amino Acid
Non-polar amino acids
Eg:- Alanine ,Glycine
Polar amino acids
Eg:- Cysteine, Serine
Positively charged amino
acids
Eg:- Histidine, Lysine
Negatively charged amino
acids
•Eg:-Aspartate, Glutamate
Aromatic amino acids
Eg:- tyrosine,
phenylalanine
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7. Classification of amino acids based on Nutrition
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8. Qualitative tests for proteins
 Biuret test:- Proteins are polypeptides of amino acids linked together by peptide
bonds. An alkaline solution of protein is treated with a drop of aqueous copper sulfate
and a bluish violet colour is obtained.
Formation of violet coloration confirms the presence of Proteins.
 Xanthoproteic test:- Proteins on treatment with nitric acid give a yellow or orange
colour. Concentrated nitric acid is used for nitration.
 Millions test:-Phenolic group of tyrosine of proteins reacts with mercuric sulfate in the
presence of sodium nitrite and sulfuric acid to give red color. Millon’s test is given by
proteins containing phenolic amino acids. The appearance of brick red color solution
confirms the presence of proteins.
 Ninhydrin test:- Proteins react with pyridine solution of ninhydrin and change to a
coloured solution from a deep blue to violet-pink or sometimes even to a red color.
Ninhydrin solution is prepared by dissolving 0.1gm of ninhydrin in about 100ml of
distilled water. But this solution of ninhydrin is unstable and can be kept for two days.
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9. Biological Role
• Digestive Enzymes:- Certain proteins act as digestive enzymes. In other words, they catabolize
nutrients into constituent monomeric units. Examples of digestive enzymes include pepsin and
amylase.
• Structural Intigrity:- Proteins are integral as they form components of certain structures.
Examples include keratin and tubulin.
• Hormonal Functions:- Hormones are paramount for regulating body functions. Insulin is one
such example.
• Transportation:-Proteins play a major role in transporting substances throughout the body.
Examples of such proteins include haemoglobin
• Defence and Protection:- Another major function of proteins is that they form a part of the
immune system and protect the body from pathogens. Example of such a protein is
immunoglobulin.
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10. Diseases related to malnutrition of proteins.
 Kwashiorkor
• This occurs due to the abandonment of
breastfeeding before the actual age due
to the birth of a younger sibling.
• Kwashiorkor may also be the outcome
of acute illness such as gastroenteritis
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11.  Marasmus
• Weight Loss
• Fat and muscle depletion
• Most common in developing countries.
• More common than Kwashiorkor
• Prevalent in children younger than those
affected by Kwashiorkor
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12. Other Symptoms of Protein Energy Malnutrition
• The symptoms of protein-energy
malnutrition or PEM are as follows:
• Apathy and irritability
• The patient becomes weak and
inefficient.
• Impaired cognition and consciousness.
• Temporary lactose deficiency
• Diarrhoea
• Hair fall
• Gonadal tissues atrophy
• Causes amenorrhea in women
• Causes libido in both men and women
• Weight loss
• Shrinking of muscles
• Protrusion of bones
• The skin gets thin, pale, dry, inelastic and
cold
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