Amino Acids.pptx

Amino acids

1. Amino Acids By, Dr. Kayeen Vadakkan Assistant Professor, Department of Biotechnology St. Mary's College Thrissur, Kerala , India

2. Amino Acids Amino acids are a group of organic compounds containing two functional groups— amino and carboxyl . The amino group (—NH2) is basic while the carboxyl group (—COOH) is acidic in nature. Amino acids bind to each other by peptide bond and form proteins.

3. General structure of amino Acids Carboxyl group Amino group

4. Classification of amino acids The classification of amino acids are done in various criteria such as Based on Structure Based on Polarity Based on Nutritional requirements

5. Based of structure amino acids are classified into 7. 1. Amino acids with aliphatic side chains. ( Example: glycine, alanine, valine, leucine) 2. Hydroxyl group containing amino acids. ( Example :Serine, threonine) 3. Sulfur containing amino acids (Example : Cysteine) 4. Acidic amino acids (Example : Aspartic acid and glutamic acid) Classification of amino acids based on Structure

6. 5. Basic amino acids. ( Example: lysine, arginine) 6. Aromatic amino acids ( Example :Phenylalanine, tyrosine and tryptophan 7. Imino acids (It has an imino group (=NH), instead of an amino group (–NH2) (Example : proline)

7. Classification of amino acids based on Polarity Based on Polarity Amino Acids 1. Non-polar amino acids. (Example : alanine, leucine, isoleucine) 2. Polar amino acids with no charge on ‘R’ group . (Example: glycine, serine, threonine) 3. Polar amino acids with positive charge on ‘R’ group. (Example: lysine, arginine and histidine) 4. Polar amino acids with negative charge on ‘R’ group. (Example: glutamic acid )

8. Classification of amino acids based on nutritional requirements Based on nutritional requirements Amino Acids 1. Essential amino acids. (Example :Arginine, Valine, Histidine, ) 2. Non essential amino acids (Example: glycine, alanine, serine)

9. Peptide bond Formation The amino acids are held together in a protein by covalent peptide bonds or linkages. These bonds are rather strong and serve as the cementing material between the individual amino acids. The peptide bond is rigid and planar with partial double bond in character. It generally exists in trans configuration. Both –C=O and –NH groups of peptide bonds are polar and are involved in hydrogen bond formation. When the amino group of an amino acid combines with the carboxyl group of another amino acid, a peptide bond is formed

10. General Chemical reactions of Amino Acids The general reactions of amino acids are mostly due to the presence of two functional groups namely carboxyl (–COOH) group and amino (–NH2) group. 1. Decarboxylation Amino acids undergo decarboxylation to produce corresponding amines.

11. 2. Formation of Amide The carboxyl group of dicarboxylic amino acids reacts with NH3 to form amide 3. Transamination Transamination is the process by which amino groups are removed from amino acids and transferred to acceptor keto-acids to generate the amino acid version of the keto-acid and the keto-acid version of the original amino acid

12. 4. Oxidative deamination Deamination is the removal of an amino group from a molecule. Enzymes that catalyse this reaction are called deaminases. The amino group is removed from the amino acid and converted to ammonia.

13. Amphoteric property of Amino acids Amino acids contain both acidic (–COOH) and basic (–NH2) groups. They can donate a proton or accept a proton, hence amino acids are regarded as ampholytes. Zwitterion or dipolar ion Zwitter ion (or dipolar ion) is a hybrid molecule containing positive and negative ionic groups. The amino acids rarely exist in a neutral form with free carboxylic (–COOH) and free amino (–NH2) groups. In strongly acidic pH (low pH), the amino acid is positively charged (cation) while in strongly alkaline pH (high pH), it is negatively charged (anion). Each amino acid has a characteristic pH (e.g. leucine, pH 6.0) at which it carries both positive and negative charges and exists as zwitterion

14. Isoelectric pH (symbol pI) is defined as the pH at which a molecule exists as a zwitterion or dipolar ion and carries no net charge. Thus, the molecule is electrically neutral. The pI value can be calculated by taking the average pKa values corresponding to the ionizable groups.

15. Titration curve of alanine The existence of different ionic forms of amino acids can be more easily understood by the titration curves. At low pH, alanine exists in a fully protonated form as cation. As the titration proceeds with NaOH, alanine loses its protons and at isoelectric pH (pI), it becomes a zwitterion. Further titration results in the formation of anionic form of alanine.

16. Titration curve of alanine 9.7 6.0 2.34 Alanine exists as cation at pH 2.34 and anion at pH 9.7. At the isoelectric pH (pI=6.0), alanine is found as zwitterion. Thus the pH of the medium determines the ionic nature of amino acids.