Extracellular Matrix and Connective Tissue

Question 1

What three classes of biomolecules are in the extracellular matrix?

Answer 1

proteoglycans, structural proteins, and specialized proteins

Question 2

Where are proteoglycans found?

Answer 2

synovial fluid of joints, arterial walls, bone and cartilage, and the ocular viterous humor

Question 3

What proteins can proteoglycans interact with?

Answer 3

collagen, elastin, fobronectin, and laminin

Question 4

Proteoglycans consist of a core protein covalently attached to what?

Answer 4

many, long, linear chains of glycosaminoglycans

Question 5

What are glycosaminoglycans made of? Characteristics?

Answer 5

• repeating disaccharide units that contain hexoamine and uronic acid
• negatively charged (repel each other) and highly hydrated (lubricant)

Question 6

How are glycoasminoglyans different?

Answer 6

They differ in the monosaccharides present in their repeating disaccharide units

Question 7

All glycosaminoglycans except ____ are attached to proteins by covalent linakages to ____ and ______ residues.

Answer 7

hyaluronic acid, serine, threonine

Question 8

Synthesis of proteoglycans

Answer 8

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)

Question 9

What is responsible for the sequential transfer of monosaccharides from a nucleotide-linked sugar to an appropriate acceptor?

Answer 9

specific UDP-sugar glycosyltransferases

Question 10

What happens after the linking sugars are attached to the protein?

Answer 10

two glycosyltransferases will alternatively add repeating monosaccharide units to the growing glycosaminoglycan

Question 11

How are sulfate groups added to proteoglycans?

Answer 11

through N- and O-sulfation (this occurs after the addition of sugars)

Question 12

What happens after the synthesis of the proteoglycan is complete?

Answer 12

it is secreted and forms the extracellular matrix

Question 13

Proteoglycan aggregate

Answer 13

formed by noncovalent interactions between core proteins and hyaluronic acid

Question 14

Function of hyaluronic acid

Answer 14

cell migration, embryogenesis, morphogenesis, wound healing

Question 15

chondroitin sulfate function

Answer 15

formation of bone, cartilage, cornea

Question 16

keratan sulfate function

Answer 16

transparency of cornea

Question 17

dermatan sulfate function

Answer 17

transparency of cornea, binds LDL to the plasma wall

Question 18

heparin function

Answer 18

anticoagulant, release lipoprotein lipase from capillary walls

Question 19

heparin sulfate function

Answer 19

component of skin fibroblast and aortic wall, commonly found on cell surfaces

Question 20

Structure of glycoproteins

Answer 20

• usually contain shorter carbohydrate chains than proteoglycans
• the carbohydrate moiety is often branched and is NOT made of repeating disaccharides

Question 21

The circulating proteins in the blood are mostly what?

Answer 21

glycoproteins

Question 22

Synthesis of glycoproteins

Answer 22

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.

Question 23

O-linked glycosides

Answer 23

begins with the attachment of an N-acetylgalactosamine onto a specific seryl or threonyl side chain of the protein

Question 24

What type of glycoproteins are integrated to the Golgi membrane with glycosyl moiety facing the Golgi lumen?

Answer 24

glycoproteins that are destined to plasma membrane

Question 25

Where are glycoproteins that are to be secreted from the cell?

Answer 25

free in the lumen

Question 26

N-linked glycosides

Answer 26

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

Question 27

Lysosomal enzymes degrade proteoglycans and glycoproteins brought into the cell by the process of ____.

Answer 27

endocytosis

Question 28

What is the carbohydrate moiety degraded by?

Answer 28

lysosomal glycosidases

Question 29

Which glycosidase cleaves carbohydrate chains to shorter oligosaccharides?

Answer 29

endoglycosidases

Question 30

Which glycosidase removes the sugar residue from the nonreducing end?

Answer 30

exoglycosidases