It is about the basics of protein which includes classification, properties, function uses.

1. Proteins
•Proteins are polymerised products of amino acids in which amino
acids are linked each other by peptide bond.
•The word protein is derived from Greek word proteios(Berzelius)
which means primary.
•Made up of chains of amino acids; classified by number of amino
acids in a chain
Peptides: fewer than 50 amino acids
Dipeptides: 2 amino acids.
Tripeptides: 3 amino acids.
Polypeptides: more than 10 amino acids
Proteins: more than 50 amino acids
Typically 100 to 10,000 amino acids linked together

2. Biology/Chemistry of Protein Structure
Primary
Secondary
Tertiary
Quaternary
Assembly
Folding
Packing
Interaction
S
T
R
U
C
T
U
R
E
P
R
O
C
E
S
S

3. Primary structure
• The primary structure refers to amino acid
linear sequence of the polypeptide chain. The
primary structure is held together by covalent
bonds such as peptide bonds,
•

4. • Primary st denotes sequences and total no of
amino acids in proteins
• Total no of a.a = molecular wt
110
• Where 110 is average mol wt of 20 strandard
amino acids in protein. Avg mol wt = 138, reduced
to 128-18=110.
• primary st of insulin has A-chain(21aa) and
B-chain(30aa)

5. Primary structure of insulin

6. Secondary structure
• Alpha helix
• Beeta sheet structure

7. ALPHA HELIX
❖ A polypeptide back bone is folded in to spiral that is held in place by hydrogen
bonds between backbone oxygen atoms and hydrogen atoms.
❖ The carbonyl oxygen of each peptide bond is hydrogen bonded to the amide
hydrogen of the a.a 4 residues toward the C-terminus
❖ Each alpha helix has 3.6 a.a per turn
❖ From the backbone side chains point outward
❖ Hydrophobic/hydrophilic quality of the helix is determined entirely by side
chains, because polar groups of the peptide backbone are already involved
H-bonding in the helix and thus are unable to affect its hydrophobic/hydrophilic.
❖ Alpha keratin of horn, hoob,, hair and nail etc, transmembrane protein
❖ Repeated seq of polar aa, similar charged aa destabilized, Glycine and Proline
❖ Opposite charged aa (3-4) at terminus stabilized, Alanine

8. ALPHA HELIX

10. THE BETA SHEET
• Consists of laterally packed beta strands
• Each beta strand is a short (5-8 residues), nearly fully extended
polypeptide chain
• Hydrogen bonding between backbone atoms in a adjacent beta strands,
within either the same or different polypeptide chains forms a beta sheet.
• Orientation can be either parallel or anti-parallel. In both arrangements
side chains project from both faces of the sheet.
• Spider’s web, reptilian claw Silk fibroin
• Large aromatic amino acids and aa isoleucine, valine, Threonine favoured
• proline

11. THE BETA SHEET

12. Tertiary Structure
• A globular
amino acid
polymer
folded and
compacted is
somewhat
functional
(catalytic)
and
energetically
favorable
interaction!

13. Quaternary Structure

14. Classification of proteins
Classification based on functions
• Contractile proteins: eg actin & myosin
• Catalytic proteins: eg enzymes
• Genetic proteins: eg histones
• Protective proteins: eg immunoglobin, interferons
• Regulatory proteins: eg GH, ACTH, insulin,glucagon,
ADH, e.t.c.
• Structural proteins: eg collagen of bone, keratin of
hair, horn, nail, hoob e.t.c.
• Transport proteins: eg Hemoglobin, transferrin etc
• Storage proteins: eg ovalbumin of egg.

15. Classification based on composition
and solubility
a. Simple proteins
• Albumins: soluble in water, coagulated by
heat,e.g. serum albumin,Ovalbumin in egg
white(albumen), lactalbumin(whey) milk
• Globulins: soluble in dilute salt solution,
coagulated by heat, alpha,beta and gamma
globulins(serum globulin), legumin
• Protamines: soluble in water, basic
protein(Lysine, Arginine), artificial insulin,
salmine from salmon, sperm protein

16. • Prolamines: contains high amount of Proline and
Glutamine, soluble in 70-80% alcohol. Eg. Gliadin
from wheat, Zein from Corn, Hordein from
Barley.
• Glutelins: soluble in dilute acids and
bases,detergents, e.g. Glutenin in Wheat,
• Scleroproteins: soluble in hot strong acids, found
in connective tissue, bone, tendons and muscle
fiber, e.g. Collagen of bone, keratin of hair horn,
nail, hoob, elastin, fibrin.

17. b.Conjugated proteins
• Glycoproteins : mucin, immunoglobulins,integral
proteins, Blood group antigens
• Lipoproteins: eg Chylomicron,VLDL,LDL , HDL
• Nucleoproteins e.g. Histone, Protamines
• Phosphoproteins : Casein, ovo-Vitellin of egg yolk
• Chromoproteins: Hb, Cytochromes, Phytochromes
• Metalloproteins :Hb, Carbonic
Anhydrase(Zinc),Monooxygenase(Cu),Arginase(Mn),ph
osphotransferase(Mg)
• Lecithoproteins: egg yolk

18. Derived Proteins:
• (A) Primary derived proteins – generally
insoluble in water
• Eg metaproteins, coagulated proteins
• (B) Secondary derived proteins – soluble in
water
• Eg proteoses, peptides, peptones

19. Classification based on shape
• Globular proteins: they are spherical or oval
in shape. They are highly soluble in water &
dilute salt solution. E.g. albumin, globulin, Hb.
• Fibrous proteins: they are elongated or
needle shaped. Their solubility is less. E.g.
collagen, keratin, elastin, fibrinogen e.t.c.

20. Classification based on nutritional
value
• Complete proteins: they contain all essential amino
acids in required proportion. E.g. albumin of egg,
casein of milk, fish, Soy.
• Partially incomplete proteins: these proteins partially
lacks one or more essential amino acid. Help for
moderate growth. E.g. pulses proteins lack in
Methionine & cereals proteins lack in Lysine.
• Incomplete proteins: these proteins comletely lack
one or more than one essential amino acid. E.g. Zein
of corn lacks in Tryptophan & Lysine and gelatin lacks
tryptophan.

21. Properties of proteins
• High mol wt compound eg insulin 5700, Hb 64450
• Solubility :colloidal solution, depends on charge
• Isoelectric PH eg Casein 4.6, Hb 6.7
• Precipitation :
by dehydration or neutralization of polar groups.
– Salting out : ammonium sulphate/ sodium sulphate.
Depends on mol wt, serum albumin is precipitated by
full saturation of ammonium sulphate while Globulin
by half saturation.(salting in)

22. – Isoelectric precipitation
– Precipitation by picric acid, tungstic acid,
Trichloroacetic acid etc reduces the positive
charge and precipited protein
– Alkaline precipitation : heavy metal ions like
Pb2+,Hg++, Cd++
– Precipitation by organic solvent : remove water
envelope

23. • Denaturation of proteins
• Denaturation can be brought about in various
ways.
• Proteins are denatured by treatment with
alkaline or acid, oxidizing or reducing agents, and
certain organic solvents, heat.
• Interesting among denaturing agents are those
that affect the secondary and tertiary structure
without affecting the primary structure. The
agents most frequently used for this purpose
are urea and guanidinium chloride.

24. • Reversible denaturation
• Irreversible denaturation