2. Course Contents
• General chemistry of amino acids
• Composition
• Amphoteric nature
• Dipeptides
• Structure of Proteins
• o Primary
• o Secondary
• o Tertiary
• Quaternary
• Functions of Proteins
• Biological importance of Proteins
• Classification of Proteins on the basis of
• o Solubility
• o Composition
• o Biological functions
• Properties of Proteins
• o Colloidal nature
• o Denaturation of Protein
3. • After the completion of this unit students will be able to:
• 1. Discuss the general structure of amino acids.
• 2. Discuss the following
• - Essential and non essential amino acid.
• - Polar and non polar amino acid
• - Zwitter ion
• 3. Describe classification of proteins according to solubility, composition,
• function and shape.
• 4. Explain the significance of protein denaturation.
• 5. Discuss the structure of dipeptides and tripeptides.
• 6. Describe the primary, secondary, tertiary and quaternary structure of protein.
4. Amino Acids
• Amino acids are the structural units that make up proteins.
• They join together to form short polymer chains called peptides or
longer chains called either polypeptides or proteins.
• These polymers are linear and unbranched, with each amino acid within
the chain attached to two neighboring amino acids.
• The process of making proteins is called translation
5. Importance
• Building blocks of proteins
• As a source of energy: CO2+Urea
• Gluconeogenesis: glucose formation.
• Flavor enhancer: glutamic acid
• Artificial sweetener: Aspartame
• 5-hydroxytryptopan: Depression treatment
6. Amino Acids
• Amino acids: structural units of proteins.
• When joined together: peptides or Proteins.
• Linear and unbranched
From: http://www.ucl.ac.uk/~sjjgsca/peptide1.gif
Date: October 25, 2015
From: http://science.halleyhosting.com/sci/ibbio/chem/notes/chpt3/primary.gif
Date: October 25, 2015
29. Isoleucine
Ile
I
Isomer of leucine: One methyl group drops one step down
From: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/L/Leu_ile.gif
Date: October 25, 2015
40. Most -Amino Acids are Chiral
• The -carbon has always
four substituents and is
tetrahedral
• All (except proline) have an
acidic carboxyl group, a basic
amino group, and an alpha
hydrogen connected to the -
carbon
• Each amino acid has an
unique fourth substituent R
• In glycine, the fourth
substituent is also hydrogen
From: https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcTyTDeiU0RySqPUeBueNvymtq1ZwKVVn8l3GVYhJ936wBEYI8WI
Date: 2014
42. Amino Acids: Classification
Common amino acids can be placed in five
basic groups depending on their R substituents:
• Nonpolar, aliphatic (7)
• Aromatic (3)
• Polar, uncharged (5)
• Positively charged (3)
• Negatively charged (2)
50. Isoelectric point
• The isoelectric point (pI) is the pH value at which the molecule
carries no electrical charge or the negative and positive
charges are equal. The PH at which amino acids are present in
zwitterion form.
51. Peptides and Peptide bonds
“Peptides” are small condensation
products of amino acids
They are “small” compared to proteins
(di, tri, tetra… oligo-)
54. Proteins
• 1: Biochemical compounds: Polymers of amino acids
• 2: Composition: one or more polypeptides (amino acids)
• 3: Structure: folded into a globular or fibrous form
• 4: Function: It carries out several biological functions.
60. Types according to composition
• Simple proteins (Only polypeptide chains)
e.g. Albumin, glubulin, glutinin, prolamin
• Conjugated proteins (Polypeptide chain + other molecules)
e.g. nucleoproteins, glycoprotein
• Derived proteins (obtained from simple proteins by the action of enzymes
and chemical agents)
e.g. Peptides i.e. proteoses (by water) and peptones (by enzymes)
61. Classification on solubility
• Proteins can be broadly classified into three groups, based on their
shape and solubility.
• Fibrous proteins: rod like structure. not soluble in water. Collagen.
• Globular proteins: spherical. soluble in aqueous solution.
Myoglobin.
• Membrane proteins: in association with lipid membranes. not
soluble in aqueous solution. Rhodopsin.
66. Secondary structure
• Folding of short polypeptide units into geometrically ordered units
• The secondary protein structure is the specific local geometric shape
caused by intramolecular and intermolecular hydrogen bonding of
amide groups.
67. Types of secondary structures
• Alpha Helix: In the alpha helix, the polypeptide chain is coiled tightly
in the fashion of a spring.
• Beta Sheets: Beta sheets consist of beta strands connected laterally
by at least two or three backbone hydrogen bonds, forming a
generally twisted, pleated sheet. A beta strand (also β strand) is a
stretch of polypeptide chain typically 3 to 10 amino acids long with
backbone in an almost fully extended conformation.
76. Fibrous proteins
• Scleroproteins: fibrous proteins,
• Examples: Keratin, collagen, elastin, and fibroin are all scleroproteins.
• The roles of such proteins include protection and support, forming
connective tissue, tendons, bone matrices, and muscle fiber.
78. • Shape: long protein filaments: rods or wires.
• Function: structural and storage
• Solubility: inert and water-insoluble.
• Occurrence: occurs as an aggregate due to hydrophobic side chains
that protrude from the molecule.
• has limited residues with repeats
• The structures often feature cross-links between chains (e.g., cys-cys
disulfide bonds between keratin chains).
• Does not denature as easily as globular proteins.
80. Globular proteins
• Globular proteins: spheroproteins
• Globular proteins are spherical ("globe-like")
• somewhat water-soluble
• they actually form colloids in water
• The term globin can refer more specifically to proteins including the
globin fold
81. Continued
• The molecule's apolar (hydrophobic) amino acids are bounded
towards the molecule's interior
• whereas polar (hydrophilic) amino acids are bound outwards,
allowing dipole-dipole interactions with the solvent, which explains
the molecule's solubility.
• folding in a different way can effect function of globular proteins
• Less stable as compared to fibrous proteins
