Proteins are made up of amino acids and perform important functions in the body. They can act as enzymes, hormones, antibodies, and structures. Amino acids are the building blocks of proteins, containing an amino group, a carboxyl group, and an R group that determines their properties. Amino acids can be classified based on their R group, charge, and essential/nonessential status. Key amino acid properties include acid-base behavior, isoelectric point, and ability to form zwitterions. Common reactions used to identify amino acids include ninhydrin, FDNB, Dansyl, and Edman reactions.

1. Protein And Their
Biochemical Role
Ms. Shalini Barad
Associate Professor
Appasaheb birnale college of Pharmacy

2. • Protein:
• Proteins are naturally occurring nitrogen containing complex
substance that consist of large number of α amino acid residues
joined by peptide linkage (CO-NH) found in all living system.
• Function:
1. Some proteins act as hormones and hence regulate various
metabolic process e.g. insulin is responsible for maintaining blood
sugar level, hormones receptor, etc.
2. Some proteins act as catalyst for biological reaction.
3. Nucleoproteins act as carrier of genetic characters.
4. Proteins are responsible for transportation of metabolite or gases
(like oxygen, CO2
) are called transport protein.
5. Some blood proteins help to form antibodies which provide
resistance to disease so called as antibodies or defense proteins.
6. Protein Which are required to give strength to cell or tissues called
structural protein viz collagen in connective tissue,keratin in hair.
7. Protein which are required to carry out mechanical work are called
muscle protein. ]
8. Haemoglobin acts as a oxygen carrier in mammals.

3. • Amino Acid
These amino acid- these are defined as a group of
organic compounds containing two functional
groups, amino group (-NH2) and carboxyl group
(-COOH) attached to α- carbon atom .
Amino acid are building blocks of proteins as protein
are the chain of the amino acid which are attached
covalently through peptide bond.
General formula of Amino acid: ( R- alkyl group)

4. All are naturally occurring amino acid have
L-configuration.
Amino acid are usually classified in α, β, γ
amino acid depending on position of
functional group from which only α amino acid
are monomer or building block of proteins.
Other way of amino acid classification based
on:

5. 1. Nature of their R group.
a) Neutral amino acid
b) Acid amino acid
c) Basic amino acid
2. On basis of their Polarity:
a) Polar side chain ( Hydrophilic nature)
-Polar amino acid with neutral charge
-Polar amino acid with positive charge
-Polar amino acid with negative charge
b) No polar side chain (hydrophobic nature)
3. On the basis of requirement:
a) Essential amino acid
b) Non Essential amino acid

6. 1. On basis of nature of R group
a) Neutral amino acid:
This is the largest group of amino acid which contains
one –COOH & one –NH2 group.
They are further divided as follow:
1. Aliphatic amino acid
These amino acid show presence of simple or branched
aliphatic side chain in R group.
Eg: Glycine (optically inactive) Leucine, Isoleucine,
Alanine, Valine, : Serine, Threonine, Asparagine,
Glutamine
2. Aromatic amino acid
This class of amino acids contain aromatic ring structure
in R group.
Eg: Phenylalanine, Tyrosine, Tryptophan

7. 3. Heterocyclic / Imino acids amino acid
This type of amino acid contain imino group (=NH) in place of
amino group (-NH)
Eg: Proline, Histidine
4. Sulphur containing amino acid
This class of amino acid contain sulphur atom in the structure.
Eg: Cysteine, Methionine
5. Hydroxyl group containing amino acid:
This type of amino acids show presence of hydroxyl group in the
structure.
Eg: Serine , Threonine

8. • Aliphatic amino acid:

9. • Aliphatic polar amino acid:

10. • Aromatic amino acid:

11. • Heterocyclic amino acid:

13. • Sulphur containing amino acid:

14. b) Acidic amino acid:
These amino acid contains two –COOH (carboxylic
group) & one –NH2 (Amino group).
Acidic amino acid are also called
monoamino-carboxylic acid.

15. c) Basic Amino Acid:
These amino acid contain one –COOH & two
–NH2 (amino group).
Basic amino acid are also called as diamino
monocarboxylic acid.

16. 2. On the basis of polarity:
1.Non polar amino acid:
Eg: Glycine (optically inactive) Leucine, Isoleucine, Alanine, Valine,
Phenylalanine, Tryptophan, Proline, Methionine.
2. Polar amino acid with no charge:
Eg: Serine, Threonine,
3.Polar amino acid with positive charge: they have more amino group
as compared to carboxyl groups making it basic .
Eg: lysine, arginine & histidine
4.Polar amino acid with negative charge: they havemore carboxylic
group as compared to amino group making it acidic.
Eg: Aspartic acid , Glutamic acid

17. 3. On the basis of requirement:
a) Essentials amino acid:
The amino acid which cannot be synthesized in the body but
are required for normal functioning of body are called as
essential amino acid. These are supplied through diet.

18. b) Non essential amino acids:
Amino acids which are synthesized in the body
& hence are not very essential for normal
functioning of body are called as non
essential amino acid.

20. • Physical Properties of Amino acid:
1. Amino acid are colourless, crystalline compounds.
2. They are soluble in water, acids & alkalies.
Polar amino acid are highly soluble in water.
Non polar amino acid are highly soluble in organic
solvents like Chloroform, ether.
3. Due to presence of basic & acidic group in the same
molecule they may be regarded as salt so most of
them posses higher melting point or melt with
decomposition
4. Except glycine all amino acid contain atleat one
asymmetric carbon atom & so they are optically
active & can exist in levo & dextro form.

21. • Acid base behaviour:
AA(amino acid) contain acidic carboxylic group & the basic
amino group, hence they are amphoteric in nature.
The amino group (NH2) can accept proton (H+) and form
cation (NH3+) & behave as base.
The carboxyl group can donate H+ and for anion (COO-).
& behave as acid.
At acidic pH the amino acids are positively charged & act as
Cation.
At basic pH they are negatively charged & act as Anion

22. • At intermediate pH, the net charge is zero, it
carries both positive and negative charges.
This pH is called Isoelectric pH.
• At the isoelectric pH, the amino acid exists as
Zwitter ion which carries equal number of
positive and negative charges and net charge
becomes zero .
• At the Isoelectric point that amino acid
becomes insoluble and precipitates out.

23. • Isoelectric(PI) pH of amino acids.
1. i.Amino acids are amphoteric in nature
2. ii. The amino group (NH2) can accept proton (H+) and form cation
(NH3).
3. iii. The carboxyl group can donate H+ and form anion (COO-).
4. iv. At acidic pH the amino acids are positively charged.
5. v. At basic pH they are negatively charged.
6. vi. At intermediate pH, it carries both positive and negative charges,
the net charge is zero, this pH is called as isoelectric pH.
7. This pH is called isoelectric pH of amino acid. Isoelectric pH is specific
for every amino acid.
8. vii. At the isoelectric pH, the amino acid exists as Zwitter ion which
carries equal number of positive and negative charges.

24. • It is calculated by following formula:
• PI = 1/2 (pKa1
+ pKa2
).
• At the Isoelectric point that amino acid becomes insoluble and
precipitates out.

25. • Zwitter ion :
• It can be defined as hybrid molecule consisting
of positive & negative ionic groups.
• AA can exist in as zwitter ion form in solution.

26. It act as acid: when donate proton
It act as base: when accept proton

27. Chemical properties of Amino acid:
1. Ninhydrin Reaction
2. 1-Fluoro 2,4-dinitro benzene (FDNB)
3. Reaction with Pheylisothiocynate (PITC)
4. Reaction with Dansyl Chloride
5. Reaction with formaldehyde
6. Reaction of Carboxyl group (-COOH)
a) Amide Formation
b) Decarboxylation
c) Ester formation

28. 7. Reaction of R group
a) Xanthoproteic reaction
b) Millon’s test
c) Glyoxylic acid test
d) Sakaguchi test
e) Sodium Nitroprusside test

29. Chemical properties of Amino acid:
1. Ninhydrin Reaction-
• AA react with ninhydrin oxidatively give
purple-violet colour.
• Paper chromatography is one of the important
technique for identifying AA using ninhydrin
reagent.

31. 2. Reaction with 1-fluoro-2,4-dinitro
benzene (FDNB)
• FDNB is called as Sanger’s Reagent.
• It react with amino group to form dinitro
phenyl derivative of amino acid

32. 3. Reaction with
phenylisothiocynate (PITC)
• PITC is called Edman’s reagent.
• It react with free amino group.
• This reaction is used to find out N-terminal
amino acid residue of polypeptides &
sequence of amino acid upto 12 to 15 amino
acid residue.

34. 4. Reaction with Dansyl Chloride:
• This reagent is used to determine the
N-terminal amino acid residue of
polypeptides.
• Amino group of free amino acid also react
with dansyl chloride.

37. 6. Reaction of carboxyl group:
1) Amide Formation
2) Decarboxylation
3) Ester formation

38. • 1) Amide formation:
• Carboxyl group of amino acid reacts with
ammonia to form amides.
• The carboxyl group of aspartic acid & glutamic
acid reacts with ammonia to form asparagine
& glutamine respectively

40. 2) Decarboxylation

41. 3) Ester formation

42. 7. Reaction of R group
a) Xanthoproteic reaction
b) Millon’s test
c) Glyoxylic acid test
d) Sakaguchi test
e) Sodium Nitroprusside test

43. 1. Xanthoproteic reaction
• This is shown by aromatic amino acid.
• AA are treated with conc. HNO3 & reaction
mixture is heated.
• Yellow colouration, on treatment with NaOH,
changes to deep orange colour.
• This is due to nitration of aromatic amino acid.
• Eg: Tryptophan, Phenylalanine & tyrosine

44. • B) Millon’s test:
• The hydroxy benzyl radical of the amino acid
react with mercuric sulphate to give red
colour.
• tyrosine give this test positive

45. C) Glycoxylic acid:
• The indole group of amino acid (tryptophan)
reacts with glycoxylic acid, in the presence of
conc. H2SO4 to give a violet ring at the
junction of H2SO4 & amino acid solution.
d) Sakaguchi reaction:
• The guanidine group of argenine react with
α-naphthol, in the presence of an alkali.
• On addition of alkaline hypobromide, it give
an intense red colour.

46. Arginine Tryptophan

47. e) Sodium nitroprusside test:
• The thiol group containing amino acid reacts
with sodium nitroprusside to give a red colour.
• Thiol group containing amino acid is cysteine.

49. Imp Questions
1. Define Protein? Give its function/ Properties?
2. Define amino acid?
3. Explain in detail classification of amino acid with
structure?
4. Explain in detail classification of amino acid on basis
of their requirement with example?
5. Draw structure of amino acid containg sulphur
atom?
6. Draw structure of amino acid which are aromatic in
nature?
7. Draw the structure of amino acid containing
hydroxyl group?

50. 8. Draw the structure of essential amino acid? (
any 4)
9. Draw the structure of optically inactive amino
acid?
10. Explain acid base behaviour of amino acid?
11. Explain the isoelectric pH of amino acid?
12. Explain zwitter ion species of amino acid?
13. Explain 1. ninhydrin
2.FDNB(Sangers reaction)
3.Dansyl reaction
4.Edman’s reaction