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POM 1a - Molecular Biology Of The Cell > Extracellular Matrix > Flashcards

Extracellular Matrix Flashcards

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1
Q

What is the ECM?

A

Complex network of proteins and carbohydrates
—> filling spaces between cells

Both fibrillar and non fibrillar components

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2
Q

What are the key functions oft he ECM?

A

Provide physical support

Determines mechanicals and physio chemical properties of tissue

Influence growth, adhesion and differentiation statuts of cells and tissues

Essential for development, tissue function and organogenesis

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3
Q

What is the connective tissue?

A

ECM + component cells

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4
Q

What are the components of connective tissues?

A

Collagens

Multi-adhesive glycoproteins

Proteoglycans

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5
Q

Examples a of collagens.

A

Type I, II, III —> fibrillar

Types IV —> non-fibrillar —> basement membrane

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6
Q

Examples of multi-adhesive glycoproteins.

A

Fibronectin, fibrinogen

Laminins —> basement membrane

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7
Q

Examples of proteoglycans.

A

Aggrecan, versican, decorin

Perlecan —> basement membrane

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8
Q

What are the different types of connective tissue?

A

Tendon and skin —> tough and flexibles

Bone —> hard and dense

Cartilage —> resilient and shock-absorbing

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9
Q

How do the different types of connective tissue come about?

A

Difference in ECM components

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10
Q

What 2 things do gene mutations affect in the ECM that can cause human disorders?

A

ECM proteins

ECM catabolism (hoe ECM molecules are broken down)

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11
Q

Examples of gene mutations affecting matrix proteins.

A

Osteogenesis imperfecta

Marfan’s syndrome —> fibrillin 1

Alport’s syndrome —> type IV collagen (alpha 5)

Epidermolysis Bullosa

Cognitive Muscle Dystrophy —> laminin 2 (alpha 2 chain)

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12
Q

Gene mutations affecting ECM catabolism examples.

A

Hurler’s syndrome —> L-alpha-iduronidase

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13
Q

Fibrotic disorders due to excessive ECM deposition.

A

Liver fibrosis —> cirrhosis

Kidney fibrosis —> diabetic nephropathy

Lung fibrosis —> idiopathic pulmonary fibrosis (IPF)

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14
Q

Disorders due to excessive loss of ECM

A

Osteoarthritis

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15
Q

What are collagens?

A

Family of fibrous proteins

Major proteins in bone, tendon and skin

Most abundant proteins in mammals

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16
Q

What is the alignment of collagen fibres like?

A

Successive layers nearly at right angles
—> resist tensile force in all direction

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17
Q

How many types of collagen exist in humans and how many genes encode them?

A

28 types

42 gene

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18
Q

What is the structure of collagen?

A

3 alpha chains —> from triple helix

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19
Q

What is the composition of Type I collagen?

A

[alpha1(I)]2 [alpha2(I)]

Heterotrimer

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20
Q

What ois the composition of Type II and III collagen?

A

[alpha1(II)]3

[alpha1(III)]3

Homotrimers

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21
Q

What is the structure of the triple helix?

A

Each chain: gly-x-y repeat —> often x proline y hydroxyproline

Chain form a left-handed helix

Three alpha chains (approx 1000 amino acids) pack together to form stiff triple helical structure

22
Q

Why must every third position in a collagen triples helix alpha chain need to be glycine?

A

Glycine is smallest amino acid so is small enough to occupy the interior of the helices with its H side chain
—> helix can pack closely together

23
Q

How are collagen fibres assembled?

A

1 alpha chain

3 alpha chains (helix)

Collagen fibril

Collagen fibre

24
Q

What are the steps in fibrillar collagen biosynthesis?

A
  1. Synthesis of pro-alpha chain
  2. Post translational modifications
    —> hydroxylation of selected prolines ans lysines
    —> glycosylation of some hydroxylysines
  3. Self-assembly of 3 pro-alpha chains into procollagen triple helix
  4. Procollagen packed into secretory vesicle (or transferred into cytoplasm)
  5. Secreted out of cell
  6. End termini cleaves
  7. Self-assembly into fibril
  8. Aggregation of collagen fibrils to form a collagen fiber
25
Q

What function do covalent cross-links in collagen have?

A

Provide tensile strength and stability

Type and extent —> tissue specific and changes with age

26
Q

Where do the covalent cross-links in collagen happen?

A

Lysine and hydroxy-lysine residues

27
Q

Why is lysine and proline hydroxylation important?

A

Contributes to interchain hydrogen bond formation

28
Q

What happens in Scurvy?

A

Vit C deficiency —> under-hydroxylated collagens
—> dramatic effects on tissue stability

29
Q

What does lysine and proline hydroxylation require?

A

Fe2+ and Vit C

30
Q

What is Ehlers-Danlos syndrome (EDS)?

A

Inherited connective tissue disorder

  • fargile skin and blood vessels
  • hyper-mobile joints
  • stretchy skin
  • loose joints

Due to mutations in collagen which affect:
—> production
—> structure
—> processing

31
Q

What are the non-fibrillar collagens?

A

Types IX and XII

Types IV

32
Q

What do types IX and XII collagen do?

A

Associate with fibrillar collagens
—> regulate organisation of collagen fibrils

33
Q

What does Type IV collagen do?

A

Network forming collagen —> in all basement membranes

N and C termini not cleaved
—> domains interact with one another to form a network

34
Q

What is the basement membrane?

A

Flexible, thin mats of ECM underlying epithelial sheets and tubes containing collagens, glycoproteins and proteoglycans

35
Q

What happens in Diabetic Nephropathy?

A

Accumulation of ECM —> highly thickened basement membrane
—> restricts renal filtration —> renal failure

36
Q

What happens in Alpert syndrome?

A

Mutation in collagen IV
—> abnormally split and laminated GBM
—> progressive loss of kidney function

37
Q

What are laminins?

A

Heterotrimeric protein —> alpha, beta and gamma chain

38
Q

What is the purpose of laminins?

A

Multi-adhesive protein —> interacts w/ variety of cell surface receptors —> integrin and dystroglycan

Can self-associate as part of basement membrane matrix

Can also interact with matrix components
—> type IV collagen, nidogen and proteoglycans

39
Q

What is Congenital muscular dystrophy

A

Absence of alpha2 chain in laminin 2

Decreases adhesion and basement membrane stability?

Muscle weakness and degeneration

40
Q

What are elastic fibres made up of?

A

Ealastin core and surrounded by microfibrils rich in protein fibrillin

Woven to limit the extent of stretching

41
Q

What is the function of elastic fibres?

A

Provide elasticity to tissues

42
Q

What is fibrillin important for?

A

The integrity of elastic fibres

43
Q

What is Marfan’s syndrome?

A

Mutation in the fibrillin-1 protein

Aberrant thickening of the aortic worth fragmentation and disarray of elastic fibres
—> can be predisposed to aortic ruptures

44
Q

What is elastin?

A

Small protein arranged in a random coil of alternating hydrophobic and hydrophilic domains

Lysine residues cross linked during formation of mature elastin

45
Q

What are fibronectins?

A

Dimmer with many diff domains
—> disulphide link at C terminal

Derived from a single gene —> alternate splicing of mRNAs give rise to different types
—> insoluble fibrillar matrix
—> soluble plasma protein

46
Q

What is the function of fibronectins?

A

Regulate:
- cell adhesion
- migration in embryogenesis
- tissue repair

Important for:
- wound healing
- helping promote blood clotting

Bind multiple ligand and cell receptors

47
Q

What are proteoglycans?

A

Core proteins w/ covalently attached glycosaminoglycan (GAG) chains

48
Q

What are GAG chains made up of?

A

Repeating disaccharide units w/ 1 or 2 sugars being an amino sugar

Sulfation/craboxylation can increase negative charge

49
Q

What are the main GAG varieties?

A

Hyaluronan

Chondroitin sulfate/Fermat an sulfate

Heparan sulfate

Keratan sulfate

50
Q

What is hyaluronan?

A

Carbohydrate chain w/out a core protein

Unsulfated

Found in highly viscous tissue

Key role in protecting the cartilaginous surface from damage

51
Q

What is aggrecan?

A

Major constituent of cartilage

Perfectly suited to resist compressive forces
—> water given up but regained once load is reduced

52
Q

What does Osteoarthritis do?

A

Erosive disease resulting in loss of ECM vis degradation

Cushioning properties of cartilage over bone ends is lost
—> aggrecan cleavage by aggrecan AES’s and metalloproteinases

POM 1a - Molecular Biology Of The Cell (18 decks)

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