2. Introduction
• Proteins, long polymers of amino acids.
• Proteins are perhaps the most versatile of all biomolecules.
• Out of the total dry body weight, ¾th are made up of proteins.
• Proteins are used for body building; all major structural and
functional aspects of the body are carried out by protein molecules.
• Biochemical functions of proteins include catalysis, transport,
contraction, protection, structure and metabolic regulation.
3. Cont..
• Proteins contain carbon, hydrogen, oxygen and nitrogen as the major
components while Sulfur and phosphorus are minor constituents.
• Nitrogen is characteristic of proteins.
• On an average, the nitrogen content of ordinary proteins is 16% by
weight.
4. Cont..
• Protein: Protein is a polymer of L-α-amino acids linked by peptide
bonds.
• Polypeptide: Polypeptide is a polymer of amino acid, but the
molecule weight less than 1000.
• Peptide : Peptide is a polymer of amino acid (< 10) linked together
by peptide bonds.
• Residue: Each amino acid unit within the polypeptide is referred to
as a residue.
5. Cont..
• Amino acids are the monomeric or building blocks of proteins joined by a
specific type of covalent linkage known as peptide bond.
• Approximately 300 amino acids present in nature, but only 20 amino acids are
found in human body.
• These 20 amino acids of proteins are often referred to as the standard or primary
or normal amino acids.
• Recently 2 more amino acid found in human body. They are Selenocysteine
(21st) and pyrrolysine (22nd).
6. Cont..
• First amino acid was asparagine in 1806.
• Last amino acid was threonine found in 1938.
• All the amino acids have trivial or common names, in some cases derived
from the source from which they were first isolated. e.g.
Asparagine → asparagus
Glutamate → wheat gluten
Tyrosine → was first isolated from cheese
Glycine → was so named because of its sweet taste.
7. Amino Acids share common Structural Features
• All 20 of the common amino acids are α-amino acids.
• They have a carboxyl group (-COOH) and an amino group (- NH2)
bonded to the same carbon atom (the α-carbon).
8. • They differ from each other in their side chains, or R groups, which
vary in structure, size, and electric charge, and which influence the
solubility of the amino acids in water.
• When R group contains additional carbons in a chain they are
designated as β, γ, δ, ε etc. proceeding from α-carbon.
9. • The standard amino acid have been assigned three letters
abbreviation and one letter symbol
ex. Glycine (Gly), Alanine (Ala), Proline (Pro).
• Exception for asparagine (Asn), glutamine (Gln), isoleucine (Ile),
tryptophan ( Trp).
10. • For all the common amino acids except glycine, the carbon is bonded to four
different groups: a carboxyl group, an amino group, an R group, and a hydrogen
atom.
• The α-carbon atom is thus a chiral center.
• Because of the tetrahedral arrangement of the bonding orbitals around the α-
carbon atom, the four different groups can occupy two unique spatial
arrangements, and thus amino acids have two possible stereoisomers.
11. • Since they are non-superimposable mirror images of each other, the two forms
represent a class of stereoisomers called enantiomers.
• All molecules with a chiral center are also optically active—that is, they rotate
the plane of the plane-polarized light.
• Special nomenclature has been developed to specify the absolute configuration of
the four substituents of asymmetric carbon atoms.
• The absolute configurations of simple sugars and amino acids are specified by
the D, L system, based on the absolute configuration of the three-carbon sugar
glyceraldehyde.
• The amino acid residues in protein molecules are exclusively L stereoisomers
12. • D-Amino acid residues have been found only in a few, generally small
peptides, including some peptides of bacterial cell walls and certain
peptide antibiotics.
• E.g.- D- serine & D- aspartic acid → Human brain
13.
14.
15. Classification of amino acids
1. Structure of the side chain of the amino acid
2. Nature or polarity of the side chain of the amino acid
3. Chemical nature of the amino Acid in Solution
4. Nutritional requirement of amino acid.
5. Metabolic product of amino acids
16. Classification based on Chemical Structure of the
amino acid
Aliphatic AA Aromatic AA Heterocyclic AA Imino AA Derived AA
Mono amino Mono amino Dibasic monocarboxylic
mono carboxylic Acid dicaboxylic acid acid
Aspartic A, Glutamic acid Lysine, Arginine
18. • Aromatic AA→ Phenylalanine, Tyrosine
• Heterocyclic AA → Tryptophan
• Immino AA→ Proline
• Derived AA
Found in protein not seen in protein Non-α AA
19. Derived amino acid found in protein
After the synthesis of proteins, some amino acid are modified e.g.
1. Hydroxy-proline
2. Hydroxy- lysine Collagen
3. Gama carboxylation of glutamic acid residue of protein → Clotting
process
4. Ribosomal protein & Histone amino acid → methylated & acetylated.
20. Derived amino acid not found in protein
• Some derived amino acids are seen in free cells e.g.
Ornithine, Citrulline, homocysteine.
Produced during the metabolism
22. NON-ALPHA AMINO ACID
• Gama amino butyric acid (GABA)→ Glutamic acid
• Beta alanine → amino group in beta position → constituent of
Pantothenic acid and
Coenzyme A
23. Functional group in amino acid
• Arginine → Guanidinium gr
• Phenylalanine → Benzene gr
• Tyrosine → Phenol gr
• Tryptophan → Indole gr
• Histidine → Imidazole gr
• Proline → Pyrrolidine gr
25. Classification based on chemical nature of the amino
acid in solution
Neutral amino acids Acidic amino acids Basic amino acids
monoamino
monocarboxylic acids
monoamino dicarboxylic
acids
Diamino monocarboxylic
acids
Glycine Serine
Alanine Threonine
Proline Cysteine
Valine Phenylalanine
Leucine Tyrosine
Isoleucine Tryptophan
Methionine Asparagine
Glutamine
Aspartic acid
Glutamic acid
Lysine
Arginine
Histidine
26. Amino acids can act as acids and bases
• The amino and carboxyl groups of amino acids, along with the
ionizable R groups of some amino acids, function as weak acids and
bases.
• When an amino acid lacking an ionizable R group is dissolved in
water at neutral pH, the α-amino and carboxyl groups create a
dipolar ion, or zwitterion (German for "hybrid ion"), which can act as
either an acid or a base.
27. • Substances having this dual (acid-base) nature are amphoteric and are
often called ampholytes (from "amphoteric electrolytes").
• A simple monoamino monocarboxylic α-amino acid, such as alanine,
is a diprotic acid when fully protonated; it has two groups, the
- COOH group and the - NH3
+ group, that can yield protons:
30. Metabolic Classification of amino acids
1. Glucogenic amino acids: Degraded to Pyruvate, α-ketoglutarate, succinyl-
CoA, fumarate, and/or oxaloacetate can be converted into Glucose.
2. Ketogenic amino acids: Degraded to acetyl-CoA and further they give rise
to ketone bodies.(acetoacetate, acetone and β-hydroxybutyrate).
3. Both glucogenic and ketogenic: Amino acids which can be converted to
glucose and ketone bodies.
32. Importance of amino acids
1. Formation of proteins
2. Formation of glucose
3. Enzyme activity: The thiol (-SH) group of cysteine has an important
role in certain enzyme activity
4. Transport and storage form of ammonia: Amino acid glutamine
play an important role in transport and storage of amino nitrogen in
the form of ammonia
33. Cont..
5. As a buffer: Histidine can serve as the best buffer at physiological pH
6. Detoxification reactions: Glycine, cysteine and methionine are
involved in the detoxification of toxic substances.
7. Formation of biologically important compounds: In addition to being
the building blocks of proteins and peptides, amino acids serve as
precursors of many kinds of biomolecules, e.g., purines, pyrimidines,
neurotransmitters, hormones, heme, and vitamins that have important
and diverse biological roles.
36. • Peptides are chains (polymer) of amino acids.
• Two amino acid molecules can be covalently joined through a peptide
bond, to yield dipeptide
• Peptide linkage is formed by the removal of a molecule of water from
the α-carboxyl group of one amino acid and the α-amino group of
another.
• Di-peptide: Two amino acids
• Tri-peptide: Three amino acids.
• Tetra-peptide: Four amino acids
• Oligo-peptide: A few amino acid(10 AA)
37.
38. Biological Important Peptides
Peptides No of amino acid No of peptide bond Example
Di-peptide 2 1 Carnosine, Anserine, Aspartame
Tri-peptide 3 2 Glutathione, Thyrotropin Releasing Hormone
Tetra-peptide 4 3 -
Penta-peptide 5 4 Enkephalins
Heaxa-peptide 6 5 -
Hectra-peptide 7 6 -
Octa-peptide 8 7 Angiotensin-II
Nano-peptide 9 8 Vasopressin, Oxytocin, Bradykinin
Deca-peptide 10 9 Angiotensin-I
39. Carnosine
• Dipeptide made up of beta-alanine and histidine
• Highly concentrated in muscle and brain tissues
• Acts as pH buffer, anti-oxidant, anti-glycating agent.
Arnesine
• A dipeptide containing β-alanine and 3-methylhistidine
• Anserine is a derivative of carnosine, which has been methylated.
• Both anserine and carnosine are capable of chelating copper.
40. Aspartame
• Made up of aspartic acid and phenylalanine.
• Used as a artificial sweetener (Sugar free).
Glutathione
• Made up of Glutamate, Cysteine, Glycine.
• Glutamine residue linked to cysteine via its ϒ- carboxyl group, followed by a conventional
peptide bond between cysteine, glycine.
• Most abundant intracellular thiol.
• Two form: Reduced state (GSH) & Oxidized state (GSSG).
41. • Function:
1. It plays an important role in maintaining the proper ratio of oxidized to reduced forms of
metabolically important thiols such as coenzyme A.
2. Helps to maintain the sulfhydryl groups of protein in reduced state.
3. Acts as a Redox buffer.
4. It serves as a reducing agent for glutaredoxin in deoxyribonucleotide synthesis.
5. Prevent hemolysis in RBC.
6. Detoxify hydrogen peroxide.
7. Transport animes and peptides across the plasma membrane.
42. Thyrotropin Releasing Hormone (TRH)
• Produced by neurons in the hypothalamus that stimulates the release of thyroid-stimulating
hormone (TSH) and prolactin from the anterior pituitary.
Enkephalins
• Pentapeptide
• Acts as a neurotransmitters in the brain.
• Act to attenuate substance P release in the dorsal horn of the spinal cord and inhibit afferent pain
fibres and reduced pain
43. Angiotensin-II
• Octapeptide
• Increase BP.
• Stimulate in release of Aldosterone.
Vasopressin
• Nanopeptide
• Release from Posterior pituitary gland.
• Primary target organ is distal convoluted tubule and collecting duct in Kidney
• To promote water reabsorption.
44. Oxytocin
• Oxytocin is a natural hormone
• Release from Posterior pituitary gland.
• Stimulates uterine contractions in childbirth and lactation after childbirth.
Bradykinin
• The activation of the kinin system
• Bradykinin is particularly important in blood pressure regulation and in
inflammatory reactions, through bradykinin ability to elevate vascular
permeability → cause vasodilatation in some arteries and veins.
45. • Beside this peptides, there are some biologically important peptides present in
the body:
1. Gastrin
2. Secretin
3. Bacitracin
4. Actinomycin
5. Gramicidin
