The document discusses collagen, a fibrous protein that is the most abundant in the human body and serves structural functions in various tissues like skin, tendons, and bones. It outlines the different types of collagen, their unique amino acid composition, and associated disorders such as Ehlers-Danlos syndrome and osteogenesis imperfecta. Additionally, it emphasizes the role of vitamin C in collagen synthesis and the consequences of its deficiency.

1. Collagen
Surendra Marasini
Lecturer, Department of Biochemistry
National Medical College, Birgunj, Nepal
17th Jan 2022

2. Overviews
• What is collagen??
• Functions of collagen??
• What are types of collagen??
• Which amino acid is repeated in collagen??
• What are the disorders related to collagen??

3. What is the difference between globular and
fibrous proteins ??
Globular proteins Fibrous Proteins
1. Compact protein structure 1. Extended protein structure
2. Soluble in water 2. Insoluble in water
3.Functios in all aspects of
metabolism (enzymes, hormones,
transport etc)
3. Function in structure of the
body. Eg: tendon, bone, cartilage,
skin etc.
4. Secondary structure is complex
(mixture of alpha helix and beta
sheet)
4. Secondary structure is simple
based on only one type (alpha
helix only)

4. What is collagen??
• Well characterized fibrous protein of extracellular matrix
that serves structural functions in the body.
• For example: collagen is found as the structural
components of the skin, connective tissue, blood vessel
walls, sclera and the cornea of the eye.
• Special mechanical properties due to unique structure,
due to combination of specific amino acids into regular
secondary structural elements.

5. Collagen continue…
• It is the most abundant protein in the human body.
• It has long rigid structure, in which three polypeptides
(referred to as α chains) are wound around one another in
a rope like triple helix

6. Functions of collagen
• Dispersed as a gel to support the structure. For example
in vitreous humor of the eye.
• Bundled as tight fibers that provide great strength. For
example in tendons.
• In the cornea of the eye, collagen is stacked, so as to
transmit light with minimum scattering.
• Occur as fibers in the bone to protect them from
mechanical shear.

7. Types of collagen
• More than 25 types
• Three polypeptide alpha (α)chains are held together by
hydrogen bonds between the chains.
• Approx. 1000 amino acids long
• Slightly different properties
• Most common is type I collagen

8. Collagens can be organized into three groups
1. Fibril forming collagens
• These have characteristic banding patterns, regular
staggered packing of the individual collagen molecules.
Tissue distribution
Type

9. Fig: electron microscopic view of collagen molecule(Fibril forming)

10. 2. Network forming collagens
• They form three dimensional mesh rather than distinct
fibrils
• Eg: type IV collagen molecules assemble into sheet or
meshwork
• Function as semipermeable filtration barrier to
macromolecules in the lungs and kidney

11. Fig: electron micrograph of network forming collagen

12. 3.Fibril associated collagen
• Bind to the surface of collagen fibrils, linking these
fibrils to one another and to the other components in the
extracellular matrix

13. Amino acid sequences in collagen
• Rich in proline and glycine, help in the formation of
triple stranded helix.
• Proline: facilitates the formation of kinks, because of its
ring structure
• Glycine: smallest amino acids, present every third
position of the polypeptide chain.

14. Most chain: poly-tripeptide, sequence: -Gly-
Pro-Hyp-

15. Triple helical structure
• Bond is formed between exposed side chains of individual
collagen monomers.
• Their aggregation results in long fibers.

16. What is the uniqueness of collagen??
• Collagen contains hydroxyproline (Hyp) and
hydroxylysine(Hyl) which are not present in other
proteins.
• Example of post translational modification
• Maximizes interchain hydrogen bond formation

17. Vitamin C is required for the prolyl hydroxylase

18. Scurvy
• Hydroxylation reactions require vitamin C as a
cofactors.
• Prolyl hydroxylase and lysyl hydroxylase unable to
function.
• Interchain H bond is impaired, collagen fibrils cannot
be cross linked.

19. Fig: legs with a 46 Years old man with scurvy

20. What is Ehler Danlos Syndrome (EDS)??
• Inheritable defect in lysyl oxidase (required for the
conversion of lysine into allyl lysine to form
mature collagen fibers)
• Or due to mutation in the amino acid sequences of
collagen types I, III or V.

21. What is Osteogenesis Imperfecta(OI)
• Also called as brittle bone syndrome
• Fractures in the intrauterine life
• Most common mutations is replacement of glycine
residue from (Glycine-X-Y-)
Fig: in utero fractures revealed by radiograph

22. 1. Scurvy is due to defect of
a) Glucose metabolism
b) Improper cross linking of collagen
c) Vitamin B complex deficiency
d) Vitamin A deficiency
2. Fractures in intrauterine life is due to
replacement of which of the following amino
acids??
a. Tryptophan b. tyrosine c. glycine d. arginine

23. 3. Most common protein in human body:
a. Collagen b. Desmin c. Keratin d. enzymes
4. Which collagen is present in glomerular basement
membrane
a. Type I
b. Type II
c. Type III
d. Type IV

24. Thank You!