Connective Tissue Flashcards
Core protein is covalently attached to multiple, long/linear chains of glycosaminoglycans
Where are proteoglycans found?
Synovial fluid, arterial walls, bone/cartilage, ocular virtuous humor, and is a major component of the extra cellular matrix
Functions of proteoglycans
Molecular sieves (due to largeness), give some flexibility to substances
Repeating disaccharide units found on proteoglycans Usually contain a hexosamine and uronic acid
How do the types of glycosaminoglycans differ?
Monosaccharides in repeating units change
Which glycosaminoglycan does not link covalently?
What proteins to 5 of 7 glycosaminoglycans covalently link to?
Serine and Threonine
Which amino acid does keratan sulfate I attach to?
How does hyaluronic acid associate with proteins?
Synthesis of proteoglycans
- Sugar attaches to serine/threonine
- UPD-sugar glycosyltransferases transfer monosaccharides from nucleotide-linked sugar to receptor
- 2 glycosyltransferases alt adding monosac.
- Sulfate groups added after sugars by PAPS
- Secreted and forms into ECM
Formed by noncovalent interactions b/t the core protein and hyaluronic acid
- Usually shorter carb chains than proteoglycans
- Carb portion is usually branched and not made of repeating disaccharides
- Make up most of the proteins circulating in the blood
- Carb monomers are added to protein (lumen of ER/Golgi)
- sugar added via O-linkage (ser, thr) or N-linkage (asn)
- Carb side chain extended by sequential addition of sugar residues to nonreducing end
- Begin w/ N-acetyl-galactosamine to specific ser or thr side chain on protein
- Lipid-linked oligosaccharide is contracted (dolichaol molecules on the membrane)
- sugars added to dolichol by membrane bound glycosyltransferases
- Oligosaccharides transferred from dolichol to asn by protein-oligosaccharide transferase in ER
Degredation of proteoglycans and glycoproteins
- Lysosomes endocytose the molecules
- Glycosidases degrade carb portion of molecules
Cleaves the carb chain to shorter oligosaccharides