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Structure and function of proteins, Classification of Amino Acids based …
Structure and function of proteins
Chemical and Physical Properties of
Amino Acids
Acid-Base and Buffer Properties of Amino Acids
The breakdown of carboxylic and amino groups makes amino acids a Zwitterion or dipolar ion in solution, depending on the pH of the medium
Amino acids = Amphoteric Compound
At physiological pH of 7.4, both carboxyl and amino groups of amino acids are completely ionized
Isoelectric point or pI
The pH at which the molecule carries no net charge
No mobility in an electrical field
Solubility and buffering capacity will be minimum at iso-electric pH
Optical Activity
Amino acids having an asymmetric carbon atom exhibit optical activity: D and L isomers
The L-amino acids occur in nature 'Natural amino acids'
D-amino acids are seen in small amounts in microorganisms and as constituents of certain antibiotics
General Reactions of Amino Acids
Due to Carboxyl Group
Decarboxylation, Amide formation
Reactions Due to Amino Group
Transamination, Oxidative deamination, Formation of carbamino compound
Reactions Due to Side Chains
Transmethylation, :Ester formation by the OH group, Reaction of the amide group, Reactions of SH group
Classification of Amino Acids
Aromatic amino acids
Phenylalanine
Tyrosine
Heterocyclic amino acids
Tryptophan
Histidine
Aliphatic amino acids
Mono amino dicarboxylic acids
Di basic mono carboxylic acids
Mono amino mono carboxylic acids
Imino acid
Proline
Classification of Amino Acids based on Nutritional Requirements
Partially essential or Semi-essential
amino acids
Histidine and arginine
Essential or Indispensable amino acids
Isoleucine, Leucine, Threonine, Lysine,
Methionine, Phenylalanine, Tryptophan, Valine
Nonessential or Dispensable amino acids
Asparagine, Aspartate, Glutamine, Glutamate,Cysteine, Glycine, Serine, Alanine, Tyrosine,Proline
Protein Structure
Secondary structure
Hydrogen bond
Two main types of secondary structure
α helix
β conformation
Parallel
Anti-Parallel
Tertiary structure
Disulfide bonds between cysteine residues
Hydrogen bonds
Ionic bonds between + ve and -ve groups.
Hydrophobic interactions between
hydrocarbon side chain of amino acids
Primary structure
N-terminus
amino group
C-terminus
carboxyl group
Linking with peptide bond
Quaternary structure
Ex. Collagen , Hemoglobin
Made up of multiple polypeptide chains
Biological Function of Protein
function
Hormonal proteins
Insulin
Regulator proteins
Membrane proteins
Transport proteins
Hemoglobin
Contractile proteins
Actin & Myosins
Storage proteins
Ovalalbumin, Casein
Defensive proteins
Antibodies
Structural proteins
Silk, Collagen, Elastin, Keratin
Enzymatic protein
DNA polymerase
Classification of Protein
Solubility properteis
Soluble in water
Ex. Albumins , Protamines
Insoluble in water
Ex. Globulins,Prolamines,Scleroprotein
Chemical composition
Simple protein
Conjugated proteins
Ex. Glycoprotein, Lipoprotein,Nucleoprotein,
Phosphorprotein,Matalloprotein,Chromoprotein
Protein configuration
Fibrous proteins
Ex,Keratin,Fiboin,Collagen
Globular proteins
Ex,Albumins,Globulins,Protamines,Enzymes,
Hormones,Trasport protein
Biological functions
Peptide Bond Formation
Covalently join the a-carboxyl group (-COOH) of each amino group (-NH2) of another by dehydration or condensation reaction
Atoms in peptide bond from a rigid, planar unit
Peptide bond has no freedom of rotation
However, the bonds involving the a-carbon can rotate freely
How Protein Fold?
Proteins are composed of amino acids
Amino acids are linked by peptide bonds to from the primary structure of a protein
There are 20 different amino acid, each with unique side chains
Yhe squence of amino acids and the chemistry of the side chains determines how the protein fold which, in turn determines the protein structure and function
Classification of Amino Acids based
on Structure