sri harshini degree&pg college

1. B.Sc BIOTECHNOLOGY – Semester II
SRI HARSHINI DEGREE & PG COLLEGE.
ONGOLE-523001.
Dr. Vemu Anil kumar M.Sc, Ph.D.nanobiotechanil@gmail.com

2. Introduction:
Amino acids
Amino group
(-NH2)
Carboxyl
group (COOH)
• AMINO CARBOXYLIC ACIDS.
• Building blocks of proteins.
• Total 200.
• Human 60.
• Use in protein synthesis 20 – Proteogenic aminoacids.

3. Proteogenicaminoacids

4. Classification:
1. Based on Incorporation in Proteins :
I. Proteogenic or Proteinogenic.
a. Manjor amino acids – Synthesis of proteins
b. Rare amino acids – Derivatives of major amino acids.
Eg: Hydroxyproline, Hydroxylysine, Aminocitric acid, Asparagine and
Glutamine.
II. Non-proteogenic.
Do not participate in protein synthesis.
Eg: Ornithine, pantothenic acid etc…

5. 2. Based on Structure of Side chain:
I. Aliphatic amino acids.
a. Monoamino monocarboxylic acids.
Glycine, Alanine, Serine, Cystine, Threonine, Methionine, Valine,
Leucine and Isoleucine.
b. Monoamino dicarboxylic acids.
Aspartic acid and Glutamic acid.
c. Diamino monocarboxylic acids.
Lysine and Arginine.
d. Diamino dicarboxylic acids.
Cystine – Dicystine.

6. 2. Based on Structure of Side chain:
II. Aromatic amino acids.
• Contain Aromatic ring.
• Monoamino monocarboxylic acids and Neutral in reaction.
• Phenylalanine, Tryptophan, Tyrosine.

7. 2. Based on Structure of Side chain:
III. Heterocyclic amino acids.
• Contain Heterocyclic ring – Imidazole ring , Indole ring.
• Proline, Hydroxyproline, Histidine.

8. 3. Based on the position of the NH2 group:
I. α - amino acids.
• C atom next to acid group.
• -NH2 is attached to α C.
• Alanine
II. β - amino acids.
• Second C atom from the acid group.
• -NH2 is attached to β C.
• Βamino propionic acid.

9. III. γ - amino acids.
• Third C atom from the acid group.
• -NH2 is attached to γ C.
• γ – amino butyric acid.
4. Based on the Reaction in solution.
I. Neutral amino acids.
• Do not contain Amino or Carboxylic group in R – side chain.
• Glycine, Alanine, Serine etc…
II. Acidic amino acids.
• Contain additional Carboxylic group in R – side chain.
• Aspartic acid, glutamic acid etc…
III. Basic amino acids.
• Contain additional Amino group in R – side chain.
• Lysine, arginine etc…

10. 5. Based on the Polarity of the side chain – Tendency to react with Water.
I. Hydrophilic amino acids.
• Side chain have high affinity to water – Charged or Uncharged
• Charged side chains attract Water dipoles.
• Positively Charged or Basic – Lysine, arginine etc…
• Negatively charged or Acidic – Aspartic acid, glutamic acid etc…
• Uncharged side chain forms Hydrogen bonds with water – Glycine, Serine…
II. Hydrophobic amino acids.
• Side chain have do not interact with water.
• Aliphatic amino acid – Alanine, valine, leucine, isoleucine.
• Aromatic amino acid – Phenylalanine, tyrosine, tryptophan etc…
• Imino acid – Proline.

11. 6. Based on the Biological importance.
I. Essential amino acids / Conditionally essential amino acids.
• Cannot be synthesised – To be included in diet – about 10 in Human.
II. Non - essential amino acids.
• Can be synthesised – Need not to be included in diet – about 10 in Human

12. 6. Based on the Configuration.
I. D - amino acids (+).
II. L - amino acids (-).
• Most common – Natural amino acids

13. Physical and Chemical properties of Amino acids
1. Solids :
• Form crystals - slender needles (tyrosine) to hexagonal plates (cystine).
2. Colour :
• Colourless.
3. Taste:
• Tasteless – Tyrosine
• Sweet – Alanine and Glycine
• Bitter – Arginine.
• Sodium glutamate – Flavoring agent.

14. 4. Solubility:
• Soluble in Water – changes with Cold/hot water.
• Soluble in dilute acids and bases.
• Slightly soluble in Alcohol.
• Insoluble in Ether.
5. Melting points:
• High MP – above 200°C, some are 300°C.
• Decompose at or near MP.
6. Optical activity:
• Optically active – Except Glycine.
• Asymmetric C atom.
• Levo rotatory (-) or Dextro rotatory (+).
• Based on pH – solvent as water or acid, Based on Cation/Anion.

15. 7. Amphoteric or Ampholyte Nature:
• Acts as Weak Acid/Base – COOH/NH2.
• Capable of Donating / Accepting Electrons.

16. 8. Zwitter ion:
• Posses both + and - charges.
• pH at which amino acid has no tendency to move either to the positive or
negative electrode – Isoelectric point (pI), Aspartic acid 2.77, Tyrosine 5.66,
Histidine 7.59, Arginine 10.76.

17. PROTEINS
• Macromolecule composed of one or more polypeptide chains or Polymer of
amino acids - Building blocks of proteins.
• Amino acid in a polypeptide is called Residue.
• Polypeptide chain with Amino group end – Amino terminal or N-terminal.
• Polypeptide chain with Carboxyl group end – Carboxyl terminal or C-terminal.
• Terminal amino acid with Free amino group is called N-terminal amino acid.
• Terminal amino acid with Free carboxyl group is called C-terminal amino acid.
• Amino acids are numbered from N – terminal.

18. Peptide bond:
• Chemical bond (Covalent) in between two amino acids.
• The α – carboxyl group of one amino acid bond to the α – amino
group of another amino acid.
• Peptide bond – Amide bond.
• Condensation or dehydration synthesis reaction.
• Dipeptide – one peptide bond, two amino acids.
• Oligopeptide – less than 10 amino acids.
• Polypeptide - more than 10 amino acids.

20. Structure of Protein
• Linderstrom – Lang : Four structural organisation.
1. Primary structure.
2. Secondary structure.
3. Tertiary structure.
4. Quaternary structure.

21. I. Primary St ruct ure:
• Linear sequence of amino acid residues making up its polypeptide chain.
• One – dimensional, not folded.
• Non – functional.
• AA arranged in a sequence (according to Genetic code).
• AA linked by Covalent bonds.
• Intermediate products of Translation - Protein synthesis.
• Formed on ribosomes.
• Precursor for secondary, tertiary and quaternary structures.

23. II. Secondary St ruct ure:
• Polypeptide chain is folded.
• Non – linear chain.
• 3 – dimensional, atoms arranged in 3 dimensions and Functional chain.
• Intramolecular bonding of AA residues by :
• 1. Covalent bonds.
• 2. Electrostatic bonds.
• 3. Hydrogen bonds.
• 4. Van der walls bonds.
• 5. Disulfide bonds.
• Chaperone proteins (cytosol) may or may not promote folding.
• Gives rise to tertiary structure.

24. The secondary structure is of two types : 1. Helical structure 2. Pleated sheets.
1. Helical structure :
• Helical structure of protein is formed by hydrogen bonds between peptide
groups within the same polypeptide chain.
• Right handed – α helix.
i. Helix is formed by series of amino acids woven in to a spiral chain.
ii. Mobility of α- carbons.
iii. Hydrogen bond is formed between of every First and Fourth residues
(CO and NH) in a regular manner to make the Turns in a regularity.
iv. Shape of the helix is maintained by Hydrogen bonds.
v. Each coil contains 3.6 amino acid residues.

25. 1.Helicalstructure:

26. 2. Pleated sheet structure :
• Pleated sheet structure of protein is formed by Hydrogen bonds between two
peptide chains.
• Bonding leads to Sheets of Parallel chains.
i. Parallel – N terminal end points in same direction. Eg: Keratin.
ii. Anti parallel – N terminal end points in opposite direction. Eg: Fibroin.
• Secondary structures were proposed by Pauling and Corey.

27. 2.Pleatedsheetstructure:

28. III. Tert iary St ruct ure:
• One polypeptide chain is involved.
• It is non-linear, globular, 3-dimensional, functional.
• Polypeptide chain is packed in to Globular structure.
• Chaperone proteins promote folding.
• Non – covalent bonds produce folding.
i. H-bond ii. Ionic bond iii. Dipole-dipole interactions iv. London dispersion forces.
• Disulfide bonds produce folding.
• R – groups are also linked addition to amino acids.
• Hydrophobic groups are packed in the core and Hydrophilic groups are
exposed.
• Give rise to Quaternary structure.

29. Eg : Myoglobin , ribonuclease.

30. IV. Qut ernary St ruct ure:
• More than One polypeptide chain is involved by Linking and Interaction.
• Intramolecular (within the polypeptide chain) and Intermolecular bonding.
• Polypeptide chains are packed in to Globular or Fibrous proteins.
• Hydrophobic part are packed in the core and Hydrophilic parts are exposed to
the surface.
• Covalent and Non-covalent bonds are involved.
i. Hydrogen bonds. ii. Ionic bonds. iii. Dipole-dipole interactions. iv. London
dispersion forces. v. Disulfide bonds. vi. Polar – non polar interactions. vii.
Hydrophilic and Hydrophobic interactions.
• Chaperone proteins promote folding.
• Non-linear, 3-dimensional, functional.

31. The quaternary structure is of two types :
1. Homogenous: Polypeptide chains are identical. Eg: Lactic acid
dehydrogenase etc.
2. Heterogenous: Polypeptides are non-indentical. Eg: Haemoglobin etc.