Download - Protein chemistry 1
PROTEIN CHEMISTRY-1AMINO ACIDS
Dr. Vijay Marakala, MBBS, MD.
BIOCHEMISTRY
IMS, MSU.
OUTLINE
Introduction
General structure of amino acid
Classification of amino acids
Importance of amino acids
Peptide bond
Biologically important peptides
LEARNING OBJECTIVES
Know the general structure of an amino acid and the structures of the 20 different R groups.
Understand how peptide bonds link amino acid residues in a polypeptide
Biomedical importance of amino acids
PROTEIN CHEMISTRY-1AMINO ACIDSIntroduction
Proteins are the most abundant molecules in living systems
Every life process depends on this class of molecules. E.g:- digestion, absorption and metabolism etc
All proteins are linear polymers of AMINO ACIDS that are linked together by covalent PEPTIDE BONDS
AMINO ACIDS
More than 300 different amino acids have been described in nature
Only as constituents of mammalian proteins.
These 20 amino acids are called STANDARD AMINO ACIDS
General structure of amino acid
C–OHH–N C
HH
R
R-group (Variable)
-carbon
side chain
O
carboxyl
All amino acids differ from each other with respect to their side chain group
amino
General structure of amino acid At physiologic pH (approximately pH 7.4)
At physiologic pH, the carboxyl group is dissociated, forming the negatively charged carboxylate ion (–COO-), and the amino group is protonated (–NH3
+).
General structure of amino acid
C
α-CARBON ATOM
β-CARBON ATOM
General structure of amino acid
Generally amino acids present in proteins are
L-α-amino acids
Classification of amino acids
I. Based on chemical structure of side chain
II. Based on nutritional requirement
III. Based on polarity of the sidechains
IV. Based on metabolic products of amino acids
Classification of amino acids
1. Aliphatic amino acids
2. Aromatic amino acids
3. Hydroxyl amino acids
4. Sulphur containing amino acids
5. Charged amino acids
6. Amide group containing amino acids
7. Imino acids
Classification of amino acidsALIPHATIC AMINO ACIDS
Unbranched amino acids Branched chain amino acids
Classification of amino acids
AROMATIC AMINO ACIDS
Classification of amino acids
HYDROXY AMINO ACIDS
Classification of amino acids
SULPHUR CONTAINING AMINO ACIDS
Classification of amino acids
CHARGED -ACIDIC AMINO ACIDS
Classification ofamino acids
CHARGED -BASIC AMINO ACIDS
Classification of amino acidsAMIDE GROUP [-CONH2] CONTAINING AMINO ACIDS
Classification of amino acids
IMINO ACIDS
Classification of amino acids
BASED ON NUTRITIONAL REQUIREMENT
Essential amino acids
Semi-essential
amino acids
Non-essential
amino acids
Classification of amino acids
BASED ON NUTRITIONAL REQUIREMENT
Essential amino acids are required for health but not synthesized in the body and therefore
have to be supplied through the diet.
Isoleucine, Leucine, Valine
Threonine,
Lysine, Methionine,
Phenylalanine, Tryptophan
PVT TIM HALL
Classification of amino acidsBASED ON NUTRITIONAL REQUIREMENT
Growing children require them in food.
But they are not essential for the adult
Histidine and arginine
Classification of amino acidsBASED ON NUTRITIONAL REQUIREMENT
These amino acids are required for health and are synthesized in the body by metabolic pathways.
Glycine, Alanine, Cysteine, Serine,
Tyrosine, Aspartic acid, Glutamic acid,
Asparagine, Glutamine and Proline.
Classification of amino acidsBASED ON POLARITY OF THE SIDECHAINS
HYDROPHILIC OR POLAR AMINO ACIDS
Acidic amino acids
Basic amino acids
Glycine, Serine, Threonine, Cysteine, Tyrosine
Glutamine and Asparagine
HYDROPHOBIC OR NON-POLAR AMINO ACIDS
Alanine, Valine, Leucine, Isoleucine
Phenylalanine, Tryptophan
Methionine
Proline
III. Based on polarity of the sidechains
Classification of amino acidsBASED ON METABOLIC PRODUCTS OF AMINO ACIDS
Leucine
Lysine, Isoleucine, Phenylalanine,
Tyrosine, Tryptophan
All other amino acids
IV. Based on metabolic products of amino acids
21st and 22nd
amino acids
BIOMEDICAL IMPORTANCE OF AMINO ACIDS
1. Formation of proteins and peptides
2. Amino acids are precursors of important biomolecules such as adrenaline, melanin, neurotransmitters, melatonin etc
3. Enzyme activity : -SH group of cysteine
4. Transport and storage form of ammonia
5. As a buffer
6. Detoxification reaction
7. Formation of biologically important compound
PEPTIDE BOND
PEPTIDE BONDS
AA 1 AA 2
AA 1 AA 2 AA 3
AA 1 AA 2 AA 3 AA 4
DIPEPTIDE
TRIPEPTIDE
TETRAPEPTIDE
Amino acid residues
PEPTIDE BOND
The linkage formed between amino acids is an amide bond called a peptide bond
This linkage formed by simple condensation of the α-carboxyl group of one amino acid with the α-amino group of another.
PEPTIDE BOND FORMATION
Biologically important peptides
Insulin – 51 amino acids
Glucagon -29 amino acids
ACTH – 39 amino acids
TRH – 3 amino acids
Oxytocin – 9 amino acids
Antidiuretic hormone – 9 amino acids
Glutathione – 3 amino acids
Next class Protein structure