CONNECTIVE TISSUE – Dr. Block Flashcards
What is the most abundant protein in the human body, its main function and about how much is in a typical person?
Collagen is the most abundant protein in the human body and serves as the body’s major fibrous framework protein. Average 150lb person has 13lbs. of collagen (8.6%).
What are the general a.a. composition characteristics of collagen? What are pre-collagen, procollagen and tropocollagen?
General A.A. composition of collagen is: 33% glycine 10% proline 10% hydroxyproline 1% hydroxylysine.
Tropocollagen is the basic structural unit that is made of 3 polypeptide alpha chains with only inter-chain hydrogen bonding for stability.
Pre-pro-collagen is the initial form of collagen synthesized on the membrane-bound ribosomes. When its signal peptide is cleaved off by signal peptidase it becomes procollagen, which can then undergo intracellular and extracellular modifications to become collagen.
Describe 4 modifications that take place to procollagen. Which one requires vitamin C?
1) Hydroxylation- which requires Vitamin C, O2, ferrous iron, alpha-ketoglutarate as well as an A.A. residue, produces succinate and a hydroxyl A.A.
2) Glycosylation is required to form a stable triple helix formation. Glucose and galactose are added by transferases.
3) N-linked Glycosylation: Takes place on certain asparagines on C-terminal end of the peptide
4) Oxidation: Occurs on certain cystine molecules to form interchain disulfide bonds before triple helix is formed.
What is elastin, its color and what is its function?
Elastin is a yellowish insoluble protein that predominants in the elastic structures of the walls of large blood vessels.
What are the similarity and differences between the a.a. compositions of collagen and elastin?
Elastin and collagen have 1/3 of their a.a. as glycine. However, valine and alanine are in much higher concentration in elastin, with proline and hydroxyproline accounting for only 10%.
What enzyme modifies lysines to a form, which will eventually cause cross-linking to occur in collagen and in elastin? What are the structures in elastin crosslinks called?
Lysyl oxidase modifies lysines (in collagen) and allyl Lysines/Lysine (in tropoelastin) to eventually cause crosslinking. In elastin, the crosslinking structures are called desmosine.
What general composition characteristic of proteoglycans makes them dramatically different from collagen or elastin?
Proteoglycans have a very high polysaccharide content (up to 95% of weight), which make them dramatically different from collagen or elastin.
What 3 general structural characteristics do proteoglycans have in common?
- repeating disaccharide units in which D-glucosamine or D-galactosamine are present
- all except keratin sulfate contain a uronic acid
- ester sulfate groups are in all except hyaluronic acid.
Name 4 different proteoglycans and give their approximate molecular weights.
In amu/dalton:
Chondroitin sulfate 0.5 - 5 X 10^4
Dermatan sulfate 1.5 - 4 X 10^4
Heparin/Heparin sulfate 10^3 to over 10^6
Hyaluronic acid 4 - 8 X 10^6
What are the 2 different types of fibronectins and what functions do they perform?
Soluble = in the plasma and other fluids. Insoluble = in extracellular matrix
Fibronectin plays a major role in adhesion of cells to one another and to surfaces, as well as maintain cell morphology.
What are the structural features of fibronectin and to what does each domain bind?
Fibronectin has 2 chains of similar size and structures joined near the carboxy terminal ends by a disulfide linkage. Each chain has 3 domains:
1) 32kD domain near carboxy terminus binds glycosaminoglycans
2) 40kD domain binds collagen
3) 140 – 150kD domain binds both cell surfaces as well as glycosaminoglycans
What processing occurs in the golgi before pro-collagen is packaged into transport vesicles for export?
O-linked glycosylation
