This document discusses different types of fibrous proteins. It begins by introducing proteins and describing their structure as polypeptide chains formed from amino acids linked by peptide bonds. It then focuses on three important fibrous proteins: collagen, elastin, and keratin. For each, it describes their structure, synthesis, properties, and applications. Collagen is the most abundant protein and forms connective tissues. Elastin provides elasticity. Keratin forms hair, nails, feathers and horns through intermolecular bonding. These proteins each have distinct structures and functions that make them vital components of living tissues.

1. Polypeptides
(Proteins)
Presented by
Devansh Gupta
M.Sc.Polymer Science
Semester 1

2. Contents
Introduction
What are amino acids?
Polypeptide Formation
Properties Of Peptide Bond
Delocalization Of Additional Electron Pair
Of C=O Bond Over Peptide Group
Fibrous Proteins
1) Collagen
2) Elastin
3) Keratin

3. Introduction
Proteins are large, complex biomolecules or
macromolecules consisting of one or more chains of
amino acids.
Here these amino acid molecules are linked together
with the help of peptide bond.
It perform multiple functions within organisms,
including catalyzing metabolic reactions, DNA
replication, responding to stimuli and transporting
molecules from one location to another.
Short chains of amino acids are called peptides.
Proteins are polypeptide molecules that contain
many peptide sub units.

4. C
O
OH
N
H
H

5. DefenseEnzyme
Support
Transportation
Contractile
Regulation
Proteins can be functionallyclassified.
Hemoglobin
AntibodyProtease
Keratin & Collagen
Actin & Myosin
Insulin
Carries O2
Fights VirusesDegrades Protein
Forms Hair
and Nails
Contracts Muscle Fibers
Controls Blood Glucose

6. Amino Acid
 Amino acids are organic molecules.
 Each Amino acid has an amino group, carboxyl group, R group and
hydrogen attached to alpha (α) carbon.
 Here it contains both acidic and basic group that’s why it act as a
amphoteric.
 Crystalline solids with high MP’s.
 Highly-soluble in water.
StructureOf AminoAcid InWater

7. How Polypeptides Are Made?
Proteins(Polypeptides) are formed through
formation of peptide bonds between amino acids.
An amino group from one residue forms an amide
bond with the carboxyl of a second residue.
Here condensation polymerization take place and
water molecule is eliminated.
Peptide linkages

8. Polypeptide Chain
 Here in above polypeptide chain the carboxyl group of the amino acid n has
formed a peptide bond, C-N, to the amino group of the amino acid n + 1.
 Each peptide unit is a planar, rigid group with known bond distances and bond
angles.
 The peptide group is planar because the additional electron pair of the C=O
bond is delocalized over the peptide group such that rotation around the C-N
bond is prevented by an energy barrier.
 The main-chain part, which is identical in all residues, contains a central a
carbon atom attached to an NH group, a C'=O group, and an H atom.
 The side chain R, which is different for different residues, is bound to the a
carbon atom.

9. Delocalization Of The Additional Electron Pair
Of C=O Bond

10. Collagen
Collagen is a most abundant fibrous protein with
a large and complex structure.
25% or more(up to 35%) of total body protein.
Major component of connective tissue.
It provides the structure, firmness and strength to
all of our internal organs.
As the age of human being increases, collagen
decreases in the body causing wrinkles and joint
weakening.

11. Structure of Collagen
 This structure
show them in a
monomer form
but when they
become polymers;
Hydrogen
bonding takes
place, between
the Oxygen and
the Hydrogen.
Collagen fibres, with the main
amino acids.
Bonds which Open up
Hydrogen Bonding
Between Oxygen and
Hydrogen

12. Collagen is a rod shaped molecule 3000Å long
and 15Å in diameter.
Made up of 3 helical polypeptide chains each
containing approx. 1000 amino acid residues.
These amino acids are arranged in a repetitious
tripeptide sequence, Gly-X-Y, in which X can be
any amino acid but is frequently a Proline and Y
is frequently a Hydroxyproline or Hydroxylysine.

13. Hydrogen bonds between the residues stabilise
the 3d structure of the tropocollagen.
Covalent bonds form between tropocollagen
molecules which stabilise the collagen fibre.
Steric repulsion between proline and
hydroproline side chain stabilise the whole helix
of collagen.

14. Functions Of Collagen
It imparts strength, support, shape and elasticity to the
tissues.
It provides flexibility, support, and movement to cartilage.
It encases and protects delicate organs like kidneys and
spleen.
Teeth(dentin) are made by adding mineral crystals to
collagen.
Collagen contributes to proper alignment of cells for cell
proliferation and differentiation.
When exposed in damaged blood vessels, it initiates
thrombus formation.

15. Synthesis of Collagen

16.  Collagen is initially synthesized as a larger
precursor polypeptide, procollagen.
 Then numerous lysyl and prolyl residues of
procollagen are hydroxylated by lysyl hydroxylase
and prolyl hydroxylase, enzymes that require
ascorbic acid as catalyst.
 Hydroxylysyl and hydroxyprolyl residues provide
additional hydrogen bonding that stabilizes the
mature protein.
 After that glucosyl and galactosyl transferases
attach glucosyl or galactosyl residues to the
hydroxyl groups of specific hydroxylysyl residues.
 Registration peptides on amino and carboxyl ends
of the alpha chain which serves as extensions.

17.  The central portion of the precursor polypeptide then associates with
other molecules to form the characteristic triple helix.
 This process is accompanied by the removal of the globular amino
terminal and carboxyl terminal extensions of the precursor
polypeptide by selective proteolysis (Procollagen
peptidase/Procollagen aminopeptidase/Procollagen
carboxypeptidase).

18.  Certain lysyl residues are modified by lysyl oxidase, a copper-
containing protein that converts ε-amino groups to aldehydes.
 Then it form a Schiff base with the ε-amino group of an
unmodified lysyl residue, which is subsequently reduced to form a
C-N single bond.
 These covalent bonds cross-link the individual polypeptides and
imbue the fiber with exceptional strength and rigidity.

21. Summary ofCollagen Synthesis
Glucosyl & Galactosyl added
by glycosyl transfarase &
galactosyl transfarase.

24. Properties Of Collagen
It remains soft and flexible under low stress and
become stiff when stress is increased.
Its melting point depends on the animal that it came
from, for example human collagen is 48°C. Collagen
from pigs and cows melt at 38°C, and collagen from
fish melts under 18°C
It’s boiling point is between 198-228°C depending
on the type of collagen.
It has a degradation temperature of 438 °C
Its relative molecular mass is 28,000amu.
Bond dissociation enthalpy of Hydrogen bond is
−393.7 ± 1.5 kJ/mol.

25. Applications of Collagen
History
From the Greek word for glue, kola, the word collagen means
"glue producer".
Collagen adhesive was used by Egyptians about 4,000 years
ago, and Native Americans used it in bows about 1,500 years
ago. The oldest glue in the world, carbon-dated as more than
8,000 years old, was found to be collagen.
If collagen is partially hydrolyzed, the three
tropocollagen strands separate into globular,
random coils, producing gelatin, which is used in
many foods, including flavored gelatin desserts.
Besides food, gelatin has been used in
pharmaceutical, cosmetic, and photography
industries.

26. Collagens are widely employed in the construction of
artificial skin substitutes used in the management of
severe burns & beauty treatments.
Collagen is also sold commercially as a joint mobility
supplement. This lacks supportive research as the
proteins would just be broken down into its base amino
acids during digestion, and could go to a variety of
places besides the joints depending upon need and DNA
orders.
Collagen is also used in Wound Healing medicines.
Collagen is used as temporary thermoplastic glues in
musical instruments like violin and guitar .

27. Elastin
Elastin is found in skin and tissues of the body.
It is a protein in connective tissue that
is somewhat elastic in nature and allows many
tissues in the body to regain their shape after
stretching or contracting.
It is a protein that helps to keep our skin flexible
but tight.
 It also helps keep skin smooth as it stretches to
accommodate normal activities like flexing a
muscle or opening and closing the mouth to talk
or eat.

28. Fiber Distribution
Lungs
Elastic ligaments
Skin
Bladder
Elastic cartilage
Blood vessels

29. Structure Of Elastin
Elastin is an cross-linked insoluble protein which
is mainly made up of amino acids like valine,
glycine, alanine and proline.
Elastin consists of linear polypeptide tropoelastin
subunits whose molecular weight is more than
72,000 amu.

30. It does not contains hydroxylysine or covalently
linked sugar residues & 1% of it is composed of
hydroxyproline.
It interconverts between number of
conformations, both disordered (on left) and b-
spiral (bottom left).
After cross-linking, when elastin is stretched or
compressed it becomes unstable and regain it’s
disordered conformational structure.

31. Synthesis Of Elastin

32. Properties Of Elastin
It shows flexible elastic nature under low stress
and become rigid when stress is increased.
It forms in the body till the age of 12-14 years
after that it can’t be formed in the body.
Its melting point depends on the animal that it
came from, for example human elastin is 45°C.
Elastin from pigs and cows melt at 35°C, and
Elastin from fish melts under 15°C.
It’s boiling point is between 155-165°C.
It has a degradation temperature of 295°C.
Its relative molecular mass is 72,000amu.

33. Applications Of Elastin
Used for skin-care products
Anti-aging creams
Skin renewing
Face treatment
Body lotion
Used as a coating on collagen patches for injuries.
The addition of an active form of elastin to the
skin’s surface has the potential to reduce the
requirement for drugs or cosmetic surgery
procedures, making it a highly cost effective and
safe alternative.

34. Keratin
Keratin is a fibrous protein and the major
component in the skin, hair, nails, horns, hoofs,
wool and feathers, the hair is totally made up of
keratin associated proteins.
It serves important structural and protective
functions, particularly in the epithelium.
It acts both as an external protective protein in the
cuticle and as an internal structural protein in the
cortex.
Some keratin have also been found to regulate key
cellular activities, such as cell growth and protein
synthesis.

35. Structure Of Keratin
Structure of keratin was first determined by
Hanukoglu and Fuchs.
Fibrous keratin molecule supercoil to form a very
stable helical filament consisting of multiple
copies of the keratin monomer.
Keratin monomer consist of amino acids such as
glycine, alanine and serine which are responsible
for the formation of inter and intra molecular
hydrogen bonds.

36. It also contains large amount of sulphur
containing amino acids like cysteine which is
required for the disulphide bridges that provides
additional strength and rigidity by permanent
and thermally stable crosslinking.
According to the structure keratin protein can be
divided in to two types.
1) Alpha keratin
2) Beta keratin
Alpha keratin, which is found in the baleen plates
of whales, horns, skin, hair and the wool are
primarily fibrous and helical in structure.

37. While beta keratin is in harder sheet form and
can be found in nails and in the scales and claws
of reptiles, their shells and in the feathers, beaks,
claws of birds and quills of porcupines.

38. Properties Of Keratin
Keratin is completely insoluble in cold or hot water.
It cannot be attacked by proteolytic enzymes.
The length and diameter of keratin fibers depends on
their water content, complete hydration (16%)
increses their length by 10 to 12%.
Due to both of the bonds hydrogen bond and
disulphide bond keratin fiber bears an outstanding
mechanical properties.
It has a degradation temperature of 400°C.
Degrades with the evolution of CO2 and Sulphur
dioxide.

39. Applications Of Keratin
Being rich in reactive chemical groups which make it
more hydrophilic and capable of interacting with
incorporating drugs, it is used as a solvent for this type
of drugs for controlled drug delivery system.
For the production of biodegradable films and coatings.
To study the in vitro skin permeability for drugs
avoiding the use of animal or human skin.
Keratin powder used as an absorbent for wound dressing
due to release of keratin derivatives to the wound.
In hair care products.
For the treatment for damaged hair .

40. That’s All