This document provides information on the structure and properties of proteins. It discusses the four levels of protein structure - primary, secondary, tertiary, and quaternary. The primary structure is the amino acid sequence. Secondary structures include alpha helices and beta sheets. Tertiary structure involves the folding of the polypeptide chain. Quaternary structure involves the assembly of multiple polypeptide subunits. Proteins are classified by function, structure, composition, and nutritional value. Proteins play many important roles in the human body and are used in various applications.

1. Ms. Jigisha Pancholi
Head
Dept. of Biochemistry & Microbiology
IIAPS
Gujarat Ayurved University

2.  A complex polymer containing carbon, hydrogen, oxygen,
nitrogen and usually sulfur & Phosphorus and composed of
chains of amino acids linked by peptide bond (−CO•NH−).
• Two amino acids = Dipeptide
• Three amino acids = Tripeptide
• Four amino acids = Tetrapeptide
• < 10 amino acids together = Oligopeptide
• 10 -50 amino acids = Polypeptide

3.  Even though there are 20 amino acids, by changing the
sequence of combination of these amino acids, nature
produces enormous number of different proteins.
 There are about 100, 000 different proteins in the human body.
 Makes 75% of the dry weight of the body.

4. • It’s a partial double bond.
• The C-N bond is ‘trans’ in nature and there is no freedom of
rotation.
• The distance is 1.32Å which is midway between single
bond(1.42Å) and a double bond(1.27Å).

5.  It can also be called an eupeptide bond to separate "it" from
an isopeptide bond, a different type of amide bond between
two amino acids.
 An isopeptide bond is an amide bond that can form for
example between the carboxyl group of one amino acid and
the amino group of another. At least one of these joining
groups is part of the side chain of one of these amino
acids.
 Lysine for example has an amino group on its side chain and
glutamic acid has a carboxyl group on its side chain.

6.  There are two ends in a peptide chain:
N- terminal end/ Amino terminal end
C- terminal end/ Carboxy terminal end
 The N-terminal amino acid is written on left hand side when
the sequence is denoted.
 Biosynthesis of protein also starts from the amino terminal
end.

7.  Primary Structure
 Secondary Structure
 Tertiary Structure
 Quaternary Structure

8.  PRIMARY STRUCTURE
• Primary structure denotes the number and sequence of amino
acids in the protein.
• Higher levels of organization are decided by this structure.
• Each polypeptide chain has a unique amino acid sequence
decided by the genes.
• The primary structure is maintained by the covalent bonds of
the peptide linkages.
• One should be very clear by the term “sequence” see e.g.
Gly-Ala-Val(1)
Gly-Val-Ala(2)

9.  Some organisms, like bacteria and fungi can also make short
peptides by non-ribosomal peptide synthesis, which often use
amino acids other than the standard 20, and may be cyclized,
modified and cross-linked.
 Non ribosomal peptides are synthesized by nonribosomal
peptide synthetases, which, unlike the ribosomes, are
independent of messenger RNA.
 Non ribosomal peptides often have cyclic and/or branched
structures, can contain non-proteinogenic amino acids including
D-amino acids, carry modifications like N-methyl and N-formyl
groups, or are glycosylated, acylated, halogenated, or
hydroxylated.

10. • Even a single amino acid change (mutation) in the linear
sequence may have profound biological effects on the function.
• For example, in HbA (normal Hb), the 6th amino acid in the
beta chain is glutamic acid; it is changed to valine in
HbS(sickle cell anemia).

11. ” denotes the configurational relationship between
residues which are about 3-4 amino acids apart in
 The spatial arrangement of polypeptide chain by twisting or
folding is called as secondary structure.
 Protein secondary structure is the three dimensional form of
local segments of proteins.
 The bonds stabilizing structure are: Hydrogen bond, electrostatic
bond, hydrophobic interaction,Vander walls bond.
 Hydrogen bond mainly stabilize the secondary structure.
 Two kinds of common secondary structures:
a. Alpha helix
b. Beta pleated sheet

13.  It is also called as Pauling–Corey–Branson α-helix.
 It is a spiral structure.
 The polypeptide bonds form the backbone and side chain of amino
acids extend outward.
 It is stabilized by hydrogen bonds between NH and C=O groups of
the main chain.
 Each turn is formed by 3.6 residues.
 Distance between each aa. residue is 1.5Å
 Right handed because amino acids found in proteins are of L-
variety.

15. α-helix

16.  The polypeptide chains are fully extended.
 The distance between adjacent a.a. is 3.5Å.
 It is stabilized by hydrogen bonds.
 Adjacent strands in a sheet can run in the same direction
(parallel) or in opposite direction (anti parallel beta sheet).

17. β- pleated sheet

18.  Three dimensional structure of the polypeptide chain.
 The tertiary structure will have a single polypeptide chain "backbone" with
one or more protein secondary structures, the protein domains.
 It is maintained by non-covalent interactions such as hydrophobic bonds,
electrostatic bonds, van der Waals forces and the disulphide bonds.
 A protein domain is a conserved part of a given protein sequence and tertiary
structure that can evolve, function, and exist independently of the rest of the
protein chain. Each domain forms a compact three-dimensional structure and
often can be independently stable and folded.
 Chaperone proteins present in R.E.R. conduct the folding of proteins.

20.  Certain polypeptides will aggregate to form one functional
protein known as quaternary structure.
 The protein will lose its function when the subunits are
dissociated.
 It is stabilized by hydrogen bonds, electrostatic bonds,
hydrophobic bonds and van der Waals forces.
 Depending on the number of the monomers, the protein may
be termed as dimer(2), tetramer(4) etc..
 Each polypeptide chain is termed as Subunit or Monomer.

21. Hemoglobin
2 alpha and
2 beta chains

22. Structure of IgG
2 heavy chains
&
2 light chains

23. Hierarchical nature of protein structure
Primary structure (Amino acid sequence)
↓
Secondary structure （α-helix, β-sheet）
↓
Tertiary structure
（Three-dimensional structure formed by assembly of
secondary structures）
↓
Quaternary structure
（Structure formed by more than one polypeptide
chains）

25.  Proteins are classified according to:
A. Function
B. Structure
C. Composition
D. Nutritional value

26.  Catalytic proteins: Enzymes like hexokinase, urease etc.
 Structural proteins: Collagen, keratin etc.
 Contractile proteins: Myosin , actin, flagellin.
 Transport proteins: Haemoglobin, myoglobin, albumin
etc.
 Regulatory proteins: Insulin, growth hormone etc.
 Genetic proteins: Histone
 Protective proteins: Antibodies, clotting factors etc.

27.  Storage Proteins: Globulins in pulses, Prolamines in cereals,
glutelins in rice, albumin in egg and casein in milk
 Toxic proteins: Ricin in castor bean, lectin in legumes, cholera toxin
 Secretory proteins: Fibroin is a protein secreted by spiders and
silkworms to form webs and cocoons.
 Exotic proteins: Antarctic fishes live in -1.9ºC waters, well below
the temperature at which their blood is expected to freeze. These
fishes are prevented from freezing by antifreeze glycoproteins
present in their body.

28.  Simple : Only made up of amino acids. Eg: Albumin, histone
etc.

29.  Conjugated: Has protein + non protein part
A. Glycoprotein: Carbohydrate+ Protein. Eg: Antibody
B. Lipoprotein: Lipid + Protein. Eg: LDL, HDL
C. Nucleoprotein: Nucleic acid + Protein. Eg: Histone, ribosome
D. Chromoprotein: Coloured pigments + Protein. Eg: Hemoglobin,
Cytochrome, hemocyanin
E. Phosphoprotein: Phosphorus + Protein. Eg: Casein
G. Metalloprotein: Metal + Protein. Eg: Hemoglobin, zinc finger

30.  Derived: Derived by degradation or denaturation of
proteins. Eg. : Coagulated proteins, peptides, fibrin from
fibrinogen etc.

31.  Globular proteins: Eg: Albumin, Globulin etc.
 Fibrous protein: Eg: Keratin, Elastin, Silk etc.

32.  Nutritionally rich proteins: Has all the essential amino
acids. Eg: Casein, egg albumin etc.
 Partially incomplete proteins: Lack one essential amino
acid. Eg: Wheat and Rice protein lacks Lysine.
 Incomplete proteins: Lack more than one essential amino
acid. Eg: Zein from corn lacks trp and lys.

33.  Proteins are essential nutrients for the human body.
 Serve as a fuel source, generating 4 kcal/ gm.

34.  Enzymes are proteins.
 Hormones are proteins.

35.  Form structural unit inside the body.
 Transport of molecules.

36.  Forms channels and carriers.
 Involved in cell signaling.

37.  Binds to DNA and helps in folding.
 Involved in cell cell adhesion.

38.  Forms the cytoskeletal network
 Forms cilia, flagella and spindle fibres.

39.  Involved in contraction of muscles.
 Protects the body from infections and blood loss.

40.  In therapy, like Insulin, vaccines, interferon etc.
 Poison like Snake poison, spider venom etc.

41.  Monoclonal antibodies are used for blood group testing
 Antibodies are used to treat diseases like rheumatoid
arthritis, multiple sclerosis, Alzheimer's disease and different
types of cancers.

42.  Antibodies are used as anti sera / anti venom

43.  Antibodies are used in ELISA, RIA and immuno
electrophoresis and diffusion reactions
 Enzymes are used in ELISA

44.  Gelatin, which is used in food and industry, is collagen that
has been irreversibly hydrolyzed

45.  Collagen has been widely used in cosmetic surgery, as a
healing aid for burn patients for reconstruction of bone and a
wide variety of dental, orthopedic, and surgical purposes.
 Both human and bovine collagen is widely used as dermal
fillers for treatment of wrinkles and skin aging

46.  Keratin is used for hair treatment
 Silk is used for making clothes

47.  Enzymes are used in diagnosis of disease, treatment, food
industry, textile industry, detergents, cosmetics, genetic
engineering etc.

48.  Whey protein is taken by the body builders to enhance muscle
mass.
 Proteases and lipases are used in washing powders to remove
biological stains

49.  Protease enzyme trypsin is added into the baby food to help
digest the food.

50.  Slimming food contain isomerase enzyme that converts
glucose to fructose
 Proteases are used to make cheese