Extracellular Matrix and Connective Tissue Flashcards
What three classes of biomolecules are in the extracellular matrix?
proteoglycans, structural proteins, and specialized proteins
Where are proteoglycans found?
synovial fluid of joints, arterial walls, bone and cartilage, and the ocular viterous humor
What proteins can proteoglycans interact with?
collagen, elastin, fobronectin, and laminin
Proteoglycans consist of a core protein covalently attached to what?
many, long, linear chains of glycosaminoglycans
What are glycosaminoglycans made of? Characteristics?
- repeating disaccharide units that contain hexoamine and uronic acid
- negatively charged (repel each other) and highly hydrated (lubricant)
How are glycoasminoglyans different?
They differ in the monosaccharides present in their repeating disaccharide units
All glycosaminoglycans except ____ are attached to proteins by covalent linakages to ____ and ______ residues.
hyaluronic acid, serine, threonine
Synthesis of proteoglycans
the protein enters the ER, then synthesis starts with the attachment of a sugar to serine or threonine residues (UDP-sugars are the substrates for proteoglycan synthesis)
What is responsible for the sequential transfer of monosaccharides from a nucleotide-linked sugar to an appropriate acceptor?
specific UDP-sugar glycosyltransferases
What happens after the linking sugars are attached to the protein?
two glycosyltransferases will alternatively add repeating monosaccharide units to the growing glycosaminoglycan
How are sulfate groups added to proteoglycans?
through N- and O-sulfation (this occurs after the addition of sugars)
What happens after the synthesis of the proteoglycan is complete?
it is secreted and forms the extracellular matrix
Proteoglycan aggregate
formed by noncovalent interactions between core proteins and hyaluronic acid
Function of hyaluronic acid
cell migration, embryogenesis, morphogenesis, wound healing
chondroitin sulfate function
formation of bone, cartilage, cornea
keratan sulfate function
transparency of cornea
dermatan sulfate function
transparency of cornea, binds LDL to the plasma wall
heparin function
anticoagulant, release lipoprotein lipase from capillary walls
heparin sulfate function
component of skin fibroblast and aortic wall, commonly found on cell surfaces
Structure of glycoproteins
- usually contain shorter carbohydrate chains than proteoglycans
- the carbohydrate moiety is often branched and is NOT made of repeating disaccharides
The circulating proteins in the blood are mostly what?
glycoproteins
Synthesis of glycoproteins
the carbohydrate monomers are added in the ER and Golgi through O-linkage or N-linkage. The carbohydrate side chain is extended by the sequential addition of sugar residues to the nonreducing end.
O-linked glycosides
begins with the attachment of an N-acetylgalactosamine onto a specific seryl or threonyl side chain of the protein
What type of glycoproteins are integrated to the Golgi membrane with glycosyl moiety facing the Golgi lumen?
glycoproteins that are destined to plasma membrane
Where are glycoproteins that are to be secreted from the cell?
free in the lumen
N-linked glycosides
a lipid-linked oligosaccharide is first constructed, then a membrane bound dolichol molecule is attached through a pyrophosphate linkage to an oligosaccharide containing N-acetylglucosamine, mannose, and glucose
Lysosomal enzymes degrade proteoglycans and glycoproteins brought into the cell by the process of ____.
endocytosis
What is the carbohydrate moiety degraded by?
lysosomal glycosidases
Which glycosidase cleaves carbohydrate chains to shorter oligosaccharides?
endoglycosidases
Which glycosidase removes the sugar residue from the nonreducing end?
exoglycosidases
