1) Amino acids are organic compounds that contain both amino and carboxyl groups. They can be classified as neutral, acidic, or basic depending on their side chains. Proteins are polymers of amino acids joined by peptide bonds. 2) Proteins have primary, secondary, tertiary, and sometimes quaternary structures that determine their shape and function. They can be simple proteins composed only of amino acids or conjugated proteins bound to non-protein groups. 3) Common protein tests include the Biuret test which detects peptide bonds and the Ninhydrin test which detects amino acids.

1. UNIT :I AMINO ACIDS AND PROTEINS:
a) Amino acids: Definition- classification- synthesis of α-amino
acid (Gabriel synthesis, Koop synthesis)- properties of amino
acids (isoelectric point, action of heat, peptide formation).b)
Proteins: Definition- classification (simple and conjugated
proteins)- structure of proteins (primary, secondary, tertiary and
quaternary)-properties of proteins (colloidal nature, isoelectric
point, denaturation, hydrolysis)- colour tests for proteins (biuret
test, ninhydrin test).

2.  Amino acids
Amino acids are bifunctional compounds containing both a
amino and a carboxylic acid group
Example:

3. Classification of amino acids
Classification based on reaction in solution
Neutral amino acids: The amino acids which do not contain any amino
group or carboxyl group in the side chain are called neutral amino acid
Example: Glycine, Alanine
Acidic amino acids: The amino acids containing additional carboxylic
groups in the side chain are called acidic amino acids
Example: Aspartic acid, Glutamic acid
Basic amino acids: The amino acids carrying an additional amino
group in the side chain are called basic amino acids
Example: Lysine, Histidine

4. Synthesis of α-amino acids
 Gabrial phthalimide synthesis
The treatment of an α-halo ester with potassium phthalimide and
subsequent hydrolysis of the product gives α-amino acid

5.  Koop synthesis
The treatment of α-keto acids with ammonia forms an imine which
on catalytic reduction gives amino acid
acid acid

6. Properties of amino acids
iso electric point
 When an ionized amino acid is placed in an electric field, it will actually migrate towards
the opposite electrode.
 Depending upon the pH of the medium, three things can happen
 The +ve form (II) will migrate to the cathode, the neutral form(zwitter ion) will not
migrate, while the –ve form (III) will migrate to the anode
 “ The pH at which the amino acid shows no tendency to migrate when placed in an
electric field is known as its isoelectric point”

8. Peptide formation
A molecule formed by joining amino acid together is called a peptide,
and the amide linkages in them are known as peptide formation

9. b) Proteins: These are complex organic nitrogenous
compounds found in all living systems.
Definition: condensation polymers of α-amino acids and
having peculiar overall structures which determines their
specific physico-logical functions in the living organism

10. Classification of Proteins
Based on the chemical nature, structure, shape and solubility, proteins are classified
as:
 Simple proteins: They are composed of only amino acid residue. On hydrolysis
these proteins yield only constituent amino acids. It is further divided into:
Fibrous protein: Keratin, Elastin, Collagen
Globular protein: Albumin, Globulin, Glutelin, Histones
 Conjugated proteins: They are combined with non-protein moiety.
 The non-protein part of the conjucated proteins is known as the prosthetic group.
so the conjugated proteins on hydrolysis yield non-protein substance in addition to
amino acids
Eg. protein prosthetic group examples
Nucleoprotein Nucleic acid nuclein
Phosphoprotein Phosphoric acid caesin
Metalloprotein metal chlorophyll

11. Protein Structure
 The primary structure of a protein consists of the amino acid sequence along the
polypeptide chain.
 Amino acids are joined by peptide bonds (-CO-NH-)
 the order of amino acids in the polypeptide chain is referred as the primary structure
 example: oxytocin contains 9 amino acid residues cysteine(2 molecules), glycine,
leucine, isoleucine, proline, asparagine, glutamine and tyrosine
 the sequence of amino acids is
cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leo-Gly amide
S S
The structure of proteins can be divided into four levels of organization:
1. Primary Structure

12. Secondary structure of protein:
 The arrangement of the polypeptide chain in space is called the secondary
structure of proteins
 The stability of the polypeptide chain against the steric strain imposed by the
bulky groups when arranged in a linear fashion linus pauling proposed a
longitudinally coiled conformation called α-helix.
 The salient features of the model are,
i. The polypeptide chain is twisted (or) coiled into a α-helix. It may be right
handed (or) left handed.
ii. The right handed α-helix is the conformation of all naturally occurring proteins.
iii. The helical arrangement brings the N-H group of one-amino acids into the close
proximity of the c=o group of the fourth amino acid in the chain.

13.  Hydrogen bonds are formed between the N-H and C=O groups which
stabilise the α-helix
 The bulky groups are projected away from the helix axis so that the helix is
rigid and free from steric strain
 each turn of the helix contains 3.6 amino acid residues and is 5.4 Ao long

14. Tertiary structure:
 The polypeptide Chain is pent or folded in three dimensions to form compact globular
domains
 A domain is the smallest unit of protein tertiary structure of independent function
 the tertiary structure is stabilised by
1. H-bonds between peptide groups
2. ionic bonds between COO- and NH3
+ groups
3. non-ionic hydrophobic bonds between non- polar R groups
4. disulphide bonds between sulphur containing anion acid residues

15. Quaternary Structure
 Quaternary Structure refers to the structure of a protein macromolecule formed
by interactions between multiple polypeptide chains.
 Each polypeptide chain is referred to as a subunit. Proteins with quaternary
structure may consist of more than one of the same type of protein subunit.
 They may also be composed of different subunits.
 Hemoglobin is an example of a protein with quaternary structure. Hemoglobin,
found in the blood, is an iron-containing protein that binds oxygen molecules.
 It contains four subunits: two alpha subunits and two beta subunits.

16. properties of proteins :
colloidal nature:
 Globular proteins form colloidal dispersions in water readily as their molecules are
very large(25Ao to 200 Ao in diameter)
 They cannot pass through the cell membranes, while true solute can urine in this
way filtered (or) dialysed and protein are retained in the blood stream
Isoelectric point:
 Like amino acids, proteins also exist as zwitter ions and have definite isoelectric
point
 The isoelectric point of a protein depends up on the nature of amino acids present
in it
Example: serum anbumin which has many acidic amino acids, has a low
isoelectric point of 4.7

17. Denaturation:
Proteins are precipitated from aqeous solution by heat, addition of acids, alkalies (or)
salt solutions and lose their activity. This is termed denaturation
Example: the boiling of egg
Hydrolysis :
Proteins are hydrolysed by acids, alkalies (or) enzymes to yield amino acids

18. Colour test for proteins
Biuret test:
 The alkaline solution of a protein gives a violet colour when treated with a few
drops of dil.copper sulphate solution
 The colour is due to the formation of a copper complex between cu2+ ions and the
peptide bonds
 A biuret is likely to form intermediate and hence the name
 This test answered by all proteins
Ninhydrin test:
 When 1 ml of Ninhydrin solution is added to 1 ml protein solution and heated,
formation of a violet colour indicates the presence of α-amino acids.
 If the amino group is substituted, different colours are produced depending on the
nature of substituent
Example: proline and hydroxy proline give yellow colour with nin hydrin