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MCD > Extracellular Matrix Biology > Flashcards

Extracellular Matrix Biology Flashcards

1
Q

What are the functions of the extracellular matrix?

A
  • Provides physical support.
  • Determines the mechanical and physicochemical properties of the tissue
  • Influences the growth, adhesion and differentiation statis of the cells and tissues with which it interacts.
  • Essential for development, organogenisis and tissue function
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2
Q

What are the components of the connective tissue?

A
  • Collagens (type I to III are fibrillar, type IV is in the basement membrane)
  • Multi-adhesive glycoproteins (fibronectin, fibrinogen, and laminins in the basement membrane).
  • Proteoglycans (aggrecan, versin, decorin, and perlecan in the basement membrane).
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3
Q

What are collagens?

A

A family of fibrous proteins found in all multicellular organisms - present in bones, tendons and skin.

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4
Q

What is the arrangement of collagen fibrils in the skin¬ mature bone¬ and cornea?

A

Successive layers are at right angles to one another, able to resist tensile force in all directions.

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5
Q

What is the structure of collagens?

A

Each collagen molecule consists of 3 a chains which form a triple helix - may consist of one or more different a chains. The a chains have a characteristic gly-x-y repeat (x is often proline, y is often hydroxyproline). This is because glycine is the smallest amino acid so can occupy the interior.

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6
Q

What chains are present in type I collagen?

A

There are two different genes that code for the chains that make type I.

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7
Q

What chains are present in type II and III collagen?

A

They only have one chain type.

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8
Q

How do collagens assemble into fibres?

A

One a chain —> three a chains —> collagen fibril —> collagen fiber

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9
Q

What are the stages of collagen biosynthesis?

A

The a chain is hydroxylated (selected prolines and lysines) and then undergoes glycolysation. The three a chains self assemble, forming a procollagen triple helix. The procollagen is secreted, and in fibrillar collagens the non-collagenous domains at the N and C terminus are removed.

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10
Q

Why do lysine and proline undergo hydroxylation in collagen synthesis?

A

Hydrogen bonds can form between chains.

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11
Q

What do prolyl and lysyl hydroxylases require?

A

Fe2+ and vitamin C, lack of vitamin C results in underhydroxylated collagens resulting in scurvy.

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12
Q

How do covalent crosslinkages form in collagen?

A

Crosslinkages form when lysine and hydroxylysine are modified. This takes place after collagen is secreted. The type and extent of cross-links is tissue specific and changes with age.

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13
Q

Why are covalent cross links present in collagen?

A

They provide tensile strength and stability.

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14
Q

What happens if there is a staggered array of collagen fibrils?

A

Ehlers Danlos syndrome - parallel bundles resist tensile force in one direction.

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15
Q

What are fibril-associated collagens?

A

Type IX and type XII collagen associate with fibrillar collagens and regulate the organisation of collagen fibrils, type IV collagen is present in all basement membranes - a network forming collagen.

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16
Q

How does type IV collagen assemble?

A

They assemble in a sheet-like network.

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17
Q

What is the function of elastic fibres?

A

Elastic fibres are important in the elasticity of tissues. Interwoven with collagen to limit the extent of stretching.

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18
Q

What is the structure of elastic fibres?

A

Elastic fibres consist of a core made up of elastin, and microfibrils which are rich in fibrillin.

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19
Q

What is Marfan’s syndrome?

A

Marfans syndrome is caused by a mutation in fibrillin-1, which can manifest in the skeletal, pulmonary an cardiovascular systems. People become predisposed to aortic ruptures.

20
Q

What is the structure of elastin?

A

Consists of two segments: hydrophobic regions and a-helical regions rich in alanine and lysine. Lysine side chains are covalently cross linked.

21
Q

What is the function of the basal laminae?

A

Basement membranes (basal laminae) are beneath epithelial sheets and tubes. In the kidney, the basal membrane of the glomerulus acts as a filter.

22
Q

What does the basal membrane contain?

A

Basal membrane contains collagens, glycoproteins, and proteoglycans.

23
Q

What is diabetic nephropathy?

A

Extracellular matrix accumulated, impinging on the capillaries and restricting renal filtration resulting in renal failure.

24
Q

What is Alport syndrome?

A

Inherited defect in type IV collagen which results in loss of kidney function and hearing loss.

25
Q

What is the gene mutation causing osteogenesis imperfecta?

A

Type I collagen

26
Q

What is the gene mutation causing Epidermolysis Bullosa?

A

Type IV collagen (a5)

27
Q

What is the gene mutation causing congenital muscular dystrophy?

A

Laminin 2 (a2 chain)

28
Q

What is the gene mutation causing hurlers syndrome?

A

L-a-iduronidase (affects ECM catabolism)

29
Q

What are the fibrotic disorders due to excessive ECM deposition?

A

Liver fibrosis (cirrhosis), kidney fibrosis (diabetic neuropathy) and lung fibrosis (silicosis).

30
Q

What is a disorder due to excessive loss of ECM?

A

Osteoartritis.

31
Q

What is the vitreous humor?

A

The jelly that fills the eye.

32
Q

What is fibrosis?

A

Too much extracellular matrix.

33
Q

What are the characteristics of ECM proteins?

A

They are large, with a modular architecture - meaning that they are composed of many protein domains. They are multifunctional because of this, and multi-adhesive (bind to various matrix components and cell surface receptors).

34
Q

What is the structure of laminins?

A

Laminins consist of 3 chains (alpha, beta and gamma). They form a cross shaped molecule, and self associate as a part of the basement membrane matrix. Also associate with type IV collagen and proteoglycans. Multi-adhesive. Of the three chains the alpha chain is longest and sticks out.

35
Q

What causes congenital muscular dystrophy? What are the effects?

A
  • Absence of a2 in lamanin 2.
  • Hypotonia (decreased muscle tension)
  • Generalised weakness
  • Deformities of the jointst
36
Q

What are fibronectins?

A

A family of closely related glycoproteins and body fluids, which may form an insoluble fibrillar matrix or a soluble plasma protein. They are a large multi domain molecule.

37
Q

How are different fibronectins synthesised?

A

They are all derived from one gene with alternate splicing at the mRNA level

38
Q

What are the roles of fibronectins?

A
  • Regulate cell adhesion and migration in embryogenesis and tissue repair.
  • Important in wound healing (promote blood clotting)
  • Form a mechanical continuum with the actin cytoskeleton.
39
Q

How does integrin bind to fibronectin?

A

It recognises the RGD motif

40
Q

What are proteoglycans?

A

Core protein with one or more glycosaminoglycan chains covalently attached, which consist of repeating disaccharides. They are very resistant to compression.

41
Q

What is hyalyronan/hyaluronic acid?

A

A carbohydrate chain, no protein. It is synthesised at the cell surface, not in the ER or Golgi. It is also insulated, consisting of many repeated disaccharides.

42
Q

What is decorin?

A

A small proteoglycan which binds to collagen fibres - essential for their formation. They ‘decorate’ the collagen.

43
Q

What is hyaline cartilage?

A

The most abundant cartilage, covers the nose, larynx, ventral end of ribs and bronchi as well as the ends of long bones. It is rich in aggrecan and cushions the ends of bones.

44
Q

How does aggrecan function?

A

Highly sulfated glycosaminoglycan chains make it negatively charged, and attract cations (eg. Na+) which causes water to follow by osmosis. This cushions the bone, as when compressed the water is given up and returns when the load is reduced.

45
Q

What is osteoarthritis?

A

There is excessive extracellular matrix degradation, meaning the cushioning properties of collagens are lost. The bones rub together, causing pain, and new bones form, causing Heberdens nodes.

46
Q

What is liver cirrhosis?

A

Excessive production of fibrous connective tissue.

47
Q

What is lung fibrosis?

A

Excess deposition of collagen.

MCD (56 decks)

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