chapter 7 section 6

Question 1

What are proteoglycans?

Answer 1

Proteins with glycosaminoglycan (GAG) chains that function on cytoplasmic and extracellular surfaces.

Question 2

What is a major function of proteoglycans?

Answer 2

Binding specific proteins via their glycosaminoglycan groups.

Question 3

What type of amino acids are involved in GAG-binding sites?

Answer 3

Basic amino acids like lysine and arginine.

Question 4

what are common motifs in protein GAG-binding domains?

Answer 4

BBXB and BBBXXB sequences

Question 5

How does charge affect GAG-protein binding?

Answer 5

Positive charges on proteins neutralize the negative charges of GAGs; more sulfation increases binding.

Question 6

Can GAG-protein interactions require specific carbohydrate sequences?

Answer 6

Yes, some interactions depend on precise sugar sequences, not just charge.

Question 7

Give an example of sequence-specific GAG binding.

Answer 7

Heparin pentasaccharide binds antithrombin III, giving anticoagulant properties.

Question 8

Why is the 3-O-sulfate in heparin important?

Answer 8

It is essential for high-affinity binding to antithrombin III.

Question 9

Where can proteoglycans be located?

Answer 9

Soluble in the extracellular matrix or as transmembrane proteins.

Question 10

Give examples of soluble proteoglycans.

Answer 10

Serglycin, versican, cartilage matrix proteoglycan.

Question 11

Give an example of a transmembrane proteoglycan.

Answer 11

Syndecan.

Question 12

How do proteoglycans function?

Answer 12

By interacting with molecules through glycosaminoglycan chains and receptor domains.

Question 13

What does syndecan associate with inside the cell?

Answer 13

The actin cytoskeleton.

Question 14

What extracellular molecule does syndecan interact with?

Answer 14

Fibronectin.

Question 15

What roles does syndecan play in the extracellular space?

Answer 15

Acts as a glue, links ECM components, helps cell-matrix binding, mediates growth factor binding.

Question 16

How can proteoglycans affect cell growth?

Answer 16

They can modulate or regulate cell growth processes.

Question 17

How do heparin and heparan sulfate influence cell proliferation?

Answer 17

they can inhibit proliferation by internalization and migration to the nucleus.

Question 18

How do proteoglycans interact with fibroblast growth factor (FGF)?

Answer 18

Bind and protect FGF from degradation, enhancing its activity.

Question 19

What is the effect of proteoglycans in the ECM on growth factors?

Answer 19

They create a reservoir of growth factors for cells.

Question 20

How does transforming growth factor β (TGF-β) interact with proteoglycans?

Answer 20

Stimulates synthesis and secretion of proteoglycans in certain cells.

Question 21

Which proteoglycan core proteins have growth factor–like domains?

Answer 21

versican and lymphocyte homing receptor.

Question 22

What might these growth factor–like domains do?

Answer 22

Possibly interact with cell membrane growth factor receptors (mechanism not fully understood).

Question 23

What role do proteoglycans play in the human knee joint?

Answer 23

They allow the joint to absorb shock during movement.

Question 24

How does articular cartilage move against the meniscus?

Answer 24

With extremely low friction.

Question 25

What are the main components of articular cartilage?

Answer 25

Mostly water, plus collagen fibers and proteoglycans.

Question 26

What forms the backbone of proteoglycan structures in cartilage?

Answer 26

Hyaluronate.

Question 27

What glycosaminoglycans are found in meniscus proteoglycans?

Answer 27

Chondroitin sulfate, dermatan sulfate, keratan sulfate.

Question 28

How do proteoglycan–hyaluronate aggregates contribute to shock absorption?

Answer 28

they are highly hydrated; water is squeezed out under compression and reabsorbed when stress is removed.

Question 29

Why does reversible hydration matter in cartilage?

Answer 29

It provides flexibility and cushions joints during physical activity.

Question 30

What gives cartilage its flexibility and resilience?

Answer 30

Cartilage matrix proteoglycan.

Question 31

How are proteoglycans arranged in cartilage?

Answer 31

coated along long hyaluronic acid filaments.

Question 32

What is the role of the NH₂-terminal domain of cartilage proteoglycan?

Answer 32

Binds hyaluronic acid with help from a link protein

Question 33

How many proteoglycan units can a single hyaluronate chain coordinate?

Answer 33

Around 100 or more units.

Question 34

How large can proteoglycan–hyaluronate aggregates be?

Answer 34

Molecular weights of 2 million or more.