1.91 Biochemisty of Connective Tissue

Question 1

What gives hyaline cartilage its flexibility and resilience?

Answer 1

Proteoglycan content

Question 2

What gives hyaline cartilage its rigidity and tensile strength?

Answer 2

Collagen Content

Question 3

How does hyaline cartilage receive nutrients?

Answer 3

No nerve or blood supply

Receives nutrients via diffusion from synovial fluid, subchondral bone and perichondrium

Question 4

What else is known about cartilage?

Answer 4

Immune privileged - break down of cartilage leads to autoimmune disease
Chondrocytes nutrient supply is slow - due to ECM
Accelerated diffusion - for nutrients
Immobilised joint – Hydroxyproline ­ in blood - collagen specific A.A.

Question 5

What do chondrocytes release?

Answer 5

Chondrocytes release cytokines stimulating osteoclastogenesis

Question 6

What do chondrocytes do when pressure is released?

Answer 6

Chondrocytes live inder pressure and if you release pressure they start to destroy even more ECM - released pressure due to damaged cartilage - release cytokines - stim breakdown of the bone below the cartilage

Question 7

What collagen maid up of?

Answer 7

• Unusual protein – 30% glycine, 30% proline/hydroxyproline; also contains hydroxylysine
• Adult Articular cartilage consists of 2/3 by dry weight collagen
• Made up of many Tropocollagen molecules aggregated together = insoluble

Question 8

What gives collagen its properties?

Answer 8

Hydrogen bonding betweeen A.A - gives collagen its properties

Question 9

How is pro collagen converted to tropocollagen?

Answer 9

Procollagen peptidases cut off the “two tails” - the n-terminal and c-terminal peptides (disulphide linked)

Question 10

What is Elhers - Danlos syndrome type VII?

Answer 10

Stretchable skin, hyper-mobile joints and short stature - two tails not chopped off

Question 11

What is tropocollagen made up off?

Answer 11

its a Type II Trans Helix
Hydrogen Bonds
Regular Composition
gly-x-x-gly-x-x-gly

Question 12

Why does scurvy occur?

Answer 12

Vitamin c is required to convert proline into hoproline

Question 13

Which amino acid is the smallest?

Answer 13

glycine

Question 14

How many types of collagen is there?

Answer 14

I-XXIX

Question 15

What stabilises collagen?

Answer 15

Covalent cross links - Aldol cross links - between aldehydes

Question 16

What is Elhers - Danlos syndrome V?

Answer 16

Lysine oxidase - aldol cross link - if enzyme is missing or damaged - arteries would rupture as blood pulses through them - lack of cross links

Question 17

Which collagens are important in cartilage structure?

Answer 17

IX and XI

Mutations in COLIX and COLXI can result in Chondrodysplasia syndromes

Question 18

Which collagen is found in OA cartilage?

Answer 18

Collagen III localisation

Question 19

What are proteoglycans?

Answer 19

• Protein and glycan (polysaccharide)
• Special class of glycoproteins
• Usually low protein, High CHO
• Polysacch. Chains – glycosoaminoglycans
○ Joined by their reducing terminal sugar residues to the protein
Gives “bottle-brush” confirmation

Question 20

What is the “bottle brush structure made up of?

Answer 20

Protein core and GAG

Question 21

What are charge are Glycosaminoglycans?

Answer 21

Highly negatively charged (-OSO3-, -COO-) - sulphate and carboxylic groups

Question 22

What an Aggrecan?

Answer 22

Cartilage proteoglycan
Aggregates - negatively charged
Globular regions - G1,G2,G3 - G1 needed for aggregation

Question 23

What is keratan sulphate and what is it made from?

Answer 23

Glycosaminoglycan 
Galactose 
1,4 linkage 
N-Acetylated 
GlcNac

Question 24

What is Chondroitin-6-sulphate?

Answer 24

Glycosaminoglycan
Glucorinic Acid - 1,3 linkage
GalNac - galactose + amine + n-acetylated
Very negative

Question 25

What are glycosaminoglycans?

Answer 25

Negative charge Repeating disaccharides Specific linkage region to the protein core

Question 26

How do aggrecan proteins aggregate?

Answer 26

• G1 – N-terminal globular region interacts with another glycosaminoglycan HYALURONAN [GlcUA - b1,3 – GlcNac]n • Hyaluronan is NOT sulphated - in synovial fluid and vitreous fluid - protein core Link protein - hyaluronan with proteoglycan PWP?

Question 27

How are proteoglycans present in the ECM?

Answer 27

Most proteoglycans are present in the extracellular matrix as multimolceular aggregates - ionic interaction - stabilised by link proteins

Question 28

What do aggregates consist of?

Answer 28

• Aggregates consist of many proteoglycan monomers bound to a single molecule of hyaluronan by an IONIC interaction This interaction is stabilised by link proteins, of which there are at least two (40,000 and 50,000 Mw) Highly negatively charged (-COO-, -SO3-) They retain large volumes of water in the extracellular matrix - due to negative charge

Question 29

What is a major function of aggregation?

Answer 29

The proteoglycans are immobilised in the collagen matrix as aggregate The proteoglycans are restrained from swelling by the collagen meshwork “ a swelling pressure” This arrangement gives cartilage its firm and flexible properties

Question 30

What would happen to the proteoglycans if collagen was removed?

Answer 30

• This arrangement gives cartilage its firm and flexible properties • If the collagen was removed, the proteoglycans would expand and form a gel • In fact, proteoglycans only occupy a fraction of their fully extended volume in the matrix The hydrated proteoglycans can be REVERSIBLY COMPRESSED by displacement of some of the water from their hydration shells - overlapping of hydration shells - intermolecular repulsive forces

Question 31

What happens during redistribution of fluid from proteoglycans?

Answer 31

Redistrubude fljid within tissue - moves slowly because proteoglycans restrain it - large bottle brushed moving past brushes also provides frictions - slows it down • The fluid is redistributed within the tissue away from the point of compression • This redistribution is only slow, because the proteoglycans entrapped in the collagen meshwork impede the flow of fluid • The bottlebrushes sliding past each other leads to a large frictional drag. Therefore, cartilage only deforms gradually under load – “A DAMPING EFFECT”

Question 32

How can reversible compressibility be lost?

Answer 32

When LanthanumChloride is added - causes precipitation proteoglycans - SOKOLOFFs experiment - Cartilage 5

Question 33

What is Thomas experiment?

Answer 33

Cartilage 6 - Papain experiment - destroys cartilage so structural function is lost