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Lily PoM MBC > Extracellular Matrix > Flashcards

Extracellular Matrix Flashcards

1
Q

What is the extracellular matrix?

A

Complex network of proteins and carbohydrates filling spaces between cells
Deposited by fibroblasts
Made up of fibrillar (fibre making ) and non fibrillar components

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2
Q

What are the key functions of the extracellular matrix?

A

Physical support
Determines the mechanical and physio chemical properties of the tissue
Influences growth, adhesion and differentiation status of the cells and Tissues with which it interacts
Essential for development tissue function and organogenesis

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3
Q

What are some components of the extracellular matrix?

A

Collagens:
Type I, II, III (fibrillar)
Type IV (basement membrane)

Multi adhesive glycoproteins:
Fibronecton, fibrinogen
Laminins (basement membrane)

Proteoglycans:
Aggrecan, Versican, decorin
Perlecan (basement membrane)

Components interact with specific cell surface receptors

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4
Q

What is the effect of having many different types of collage and different orientations?

A

Allows for a range of connective tissue

Tendon and skin
Tough and flexible

Bone
Hard and dense

Cartilage
Resilient and shock absorbing

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5
Q

What are collagens?

A

Family of fibrous proteins

Major proteins in bone tendons and skin

Most abundant proteins in mammals (25% of total protein mass)

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6
Q

How is collagen arranged in The skin?

A

Successssive layers are ages at almost right angles (like ply wood)

Bone and cornea have the same arrangement

Allows them to resist tensile force

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7
Q

There are many (28) collagen types in humans (encoded by 42 genes). What is a collagen molecule comprised of?

A

Three a (alpha) chains, forming a triple helix

Can be one or more different a chains

E.g
Type I collagen has two different chains (heterotrimer)
[a1(I)]2 [a2(I)]

Types II and III are homorrimers
[a1(II)]3 and [a1(III)]3

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8
Q

What are some features of the triple helix of a collagen molecule?

A

Each alpha chain is made of a Gly-x-y repeat
Glycine and two other amino acids
X is often proline and y is often hydroxyproline

Three alpha chains form a stiff triple helical structure, every third position must be a glycine
Why? It’s is small. R group is a hydrogen only so it is the smallest aa
Fits into the centre of the triple helix

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9
Q

How do collagen fibres assemble?

A 
One alpha chain
—> 
Three alpha chain helix 
—>
Collagen fibril
—> 
Collagen fibre
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10
Q

What is the process of collagen synthesis?

A

Procollagen
With non collagenous ends at the n-terminal and c-terminal

—>

Collagen
The non collagenous ends are removed when fibrillar collagens leave the cell, but remain if the collagen stays inside the cell

—>

Fibril formation

—>

Cross linking

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11
Q

What are the steps in collagen biosynthesis (sciency)?

A

Synthesis of pro alpha chain

Post translational modifications (hydroxylation of some prolines and lysines) (glycosylation of hydroxylysines)

Self assembly of three alpha chains

Procollagen triple helix formation

EITHER put into a secretory vesicle OR transported from the golgi into the cytoplasm

If it leaves the cell, cleavage of polypeptide non collagenous ends

Then self assembly into fibrils…

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12
Q

What are some features of the cross links in collagen?

A

Provide tensile strength and agility

Involves lysine and hydroxylysine residues

Different tissues form different cross links

The type and extent of cross links is tissue-specific and changes with age

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13
Q

What is the role of lysine and proline hydroxylation?

A

Prolyl and Lysyl hydroxylases require Fe2+ and vitamin c to work

The hydroxylation allows hydrogen bonds to form between molecules allowing cross Links to be formed, giving extra strength

Covenant crosslibkages are also formed (after it has been secreted)

Vitamin c deficiency causes scurvy

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14
Q

What is Ehlers danlos syndrome?

A

Disorder of the connective tissue

Cause by mutations in collagen, including collagen production, structure and processing

Causes teeth to skin and loose joints

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15
Q

What are some types of non fibrillar collagen?

A

XI, XII
Fibril associated collagens: associate with fibrillar collagens and regulate the organisation of the fibrils

IV
Network forming collagen
Present in basement membranes

All more flexible structure
Disrupted helixes making them bendy

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16
Q

What happens in collagen type IV assembly?

A

The N and C terminals on the end of the triple helix aren’t cleaved
They undergo rotary shadowing to form a layered network

Monomer
Dimer
Tetramer
Supramolecular aggregate

For basement membrane formation

17
Q

Where would you find basement membranes?

A

Surrounding muscle, peripheral nerve , fat cells and underlying most epithelia

Also the kind at forming a key part of ultra filtration as the Glomerular basement membrane (GBM)

18
Q

What happens in diabetic nephropathy?

A

There is an accumulation of extracellular matrix leading to a highly thickened basement membrane

Restricts renal filtration and can lead to renal failure

19
Q

What is Alport syndrome

A

Mutations in collagen IV result in an abnormally split and laminated GBM which is associated with a progressive loss of kidney function and hearing loss

20
Q

What do elastic fibres consist of?

A

A core made up of the protein elastin, and microfibrils that are rich in the protein fibrillin

21
Q

What is marfans syndrome?

A

Mutation in the protein fibrillin-1
Involves complications of the skeletal, ocular and cardiovascular sysytems
And arachnosactyly

22
Q

What is the structure of elastin?

A

Alternating segments along the polypeptide chain: hydrophobic region and alpha helical regions Rich in alanine and lysine
Many lysine Chains are covelantly cross linked

23
Q

What does the modular architecture of ECM proteins mean?

A

They are composed of characteristic protein domains of 50-200 amino acids.
Results in their multifunctionality
Many larger proteins are multi adhesive, binding various matrix components and cell surface receptors

24
Q

What is the structure of laminins?

A

Heterotrimeric proteins
Made up of an alpha beta and gamma chain
Forms a cross shaped molecule
Multi adhesive proteins
Interact with a variety of cell surface receptors (integrins and dystroglycan)
They can self associate as a part of the basement membrane
But also associate with other matrix components such as type IV collagen

25
Q

What are fibronectins?

A

A family of closely related glycoproteins
Found in the ECM and other bodily fluids
They can exist as either an insoluble fibrillar matrix, or a soluble plasma protein
Derived from a single gene
Multi adhesive proteins
Made up of a large multi domain molecule linked together by disulphide bonds
Interact with other matrix components and cell surface receptors
Important in wound healing and clotting

26
Q

What are proteoglycans?

A

Core proteins covantly bonded to one of more glycosaminoglycan (GAG) chains

27
Q

What is a GAG chain

A

Repeating disaccharide units with one of the two sugars being an amino sugar
Many are surfaced or carboxylated and therefore carry a high negative charge
This attracts a cloud of cations
This results in large amounts of water being drawn into the matrix

28
Q

What are 4 proteoglycan families?

A

Basement membrane proteoglycans
Aggregating proteoglycans
Small leucine rich
Cell surface

29
Q

What are the four groups of GAG chains?

A

Hyaluronan (hyaluronic acid)
Chondroitin sulfate or dermatan sulfate
Heparan sulfate
Keratin sulfate

30
Q

What is the structure of hyaluronan?

A

Unlike other GAGs doesn’t have a protein core. Only alternationgbchain if disaccharides
Unsulfated
Can undergo a huge amount of polymerisation so has a large molecular weight and take up a lot of space

31
Q

What is aggrecan?

A

Major constituent of the ECM of cartilage
It’s GAGs are highly sulfated, increasing their negative charge
Also many negative carboxyl groups
This attracts lots of Na+ ions
So lots of wather is drawn into the matrix

This allows the cartilage to resist compressive forces
The water is given up under compression but regained when the load is reduced

32
Q

What is osteoarthritis?

A

Erosive disease resulting in excessive ECM degradation
The cushioning properties of the cartilage over bones are lost
With increasing age aggrecan is cleaved by aggrecanases
Resulting in a loss of aggrecan fragments to the synovial fluid

Lily PoM MBC (15 decks)

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