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Hilary Term 1 > Animal extracellular matrix and plant cell wall > Flashcards

Animal extracellular matrix and plant cell wall Flashcards

1
Q

Describe animal connective tissue

A
  • elastin fibres
  • collagen fibres
  • cells
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2
Q

Describe plant mesophyll tissue

A
  • cells
  • cell walls
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3
Q

Describe the extracellular matrix

A
  • assembled by all cells
  • 3D network of macromolecules surrounding cells that is outside of the cell membrane
  • all components are synthesised by the cells
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4
Q

Give some examples of extracellular matrices

A
  • archaeal cell walls
  • bacterial peptidoglycan cell walls
  • bacterial outer ‘membrane’
  • gungal cell walls of chitin
  • plant cell walls
  • animal extracellular matrix
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5
Q

ECM

A

extracellular matrix

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6
Q

Describe the ECM functions

A
  • structural support
  • protection against mechanic, biochemical and biotic stresses
  • signalling
  • regulator of cellular activities
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7
Q

Describe the structural support provided by the ECM

A

maintaining cell integrity, cell adhesion, tissue organization

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8
Q

Describe the role of the ECM in signalling

A
  • perception and transmission of mechanical and chemical signals from the environment
  • cell-cell communication
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9
Q

Describe the ECM as a regulator of cellular activities

A

growth, motility and morphogenesis

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10
Q

Describe eukaryotic ECMs

A
  • fiber-reinforced composite structures
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11
Q

Describe the major components of the eukaryotic ECMs

A
  • fibrils
  • fibril crosslinkers
  • gel
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12
Q

Describe fibrils

A
  • provides strength/ stiffness/ elasticity
  • protect against tension and compression
  • insoluble
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13
Q

Describe fibril cross linkers

A
  • organise 3D fibril network
  • strengthen it
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14
Q

Describe the gel

A
  • fibril network embedded into it
  • ensures hydrophilic environment
  • hydration
  • protects against compression
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15
Q

Describe the cell wall ECM

A
  • pectin
  • cellulose
  • microfibril
  • hemicellulose
  • soluble proteins
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16
Q

The ECM is the predominant feature in tissues with

A

a mechanical function In connective tissues

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17
Q

ECM mostly synthesised by

A

fibroblasts

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18
Q

Describe the proteinous elements of the ECM

A
  • linear collagen fibrils and cross linkers
  • elastin
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19
Q

Describe elastin

A
  • protein
  • builds an elastic protein network
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20
Q

What are fibril cross linkers composed of?

A

collagen

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21
Q

Describe collagen in the ECM

A
  • fibrils and crosslinkers
  • porous sheets
  • basal lamina
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22
Q

Describe polysaccharides in the ECM

A
  • GAGs
  • proteoglycans
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23
Q

GAGs

A

Glycosaminoglycans polysaccharide

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24
Q

Describe proteoglycans

A

core of protein with attached glycosaminoglycans

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25
Q

Describe collagen

A
  • insoluble fibrous protein
  • most abundant protein in the animal kingdom
  • 3aa repeats; every 3rd GXY
  • rich in proline, lysine and hydroxyproline
  • triple helix
  • each chain has ca. 1050 amino acids wound in a right hand triple helix
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26
Q

Describe the effect of the amino acid composition of collagen

A

lends stability to the helix

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27
Q

Describe collagen biosynthesis

A
  • synthesis and translocation of pro-alpha chain at ER
  • hydroxylation of selected prolines and lysines using vitamin C at ER
  • glycolsylation of selected hydroxylysines at the ER
  • self-assembly of 3 pro-alpha chains at the ER
  • N-linked glycan modifications at Golgi
  • procollagen triple helix formation in a secretory vesicle
  • secretion out of plasmamembrane
  • cleavage of propeptides by extracellular proteases in ECM
  • self-assembly into fibril (100-300nm) in ECM
  • aggregation of fibrils to fibre (0.5-3micrometres) in ECM
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28
Q

Collagen helices are cross-linked at

A
  • specific, regular positions
  • can be viewed under SEM
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29
Q

Describe the crosslinkers

A
  • fibril-associated collagen
  • collagen trihelix structure interrupted by one or two non-helical domains
  • important for interaction with other molecules in the ECM: determinants of fiber network
  • especially important in cartilage, ligaments and tendon
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30
Q

Describe network-forming collagen

A
  • assemble into a triple helix with non-helical breaks
  • introduces flexibility into the molecule
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31
Q

Describe Type IV collagen

A

self-assemble into a sheet-like meshwork to help form basal laminae

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32
Q

Describe basal laminae

A
  • interact with other major protein components (laminin, perlecan)
  • underlie all epithelial cell sheets and tubes
  • surround individual muscle, fat and Schwann cells
  • structural and filtering roles
  • determine cell polarity
  • influence cell metabolism
  • organise proteins in adjacent PM
  • induce cell differentiation
  • serve as “highways” for cell migration
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33
Q

Describe the basal lamina in muscle cells

A
  • connects to the connective tissue
  • surrounded by the PM
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34
Q

Describe the basal lamina in epithelial sheets

A
  • connected to connective tissue
  • lumen
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35
Q

Describe the basal lamina in the kidney glomerulus

A
  • connects to endothelial cells
  • epithelial cells
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36
Q

Describe elastin

A
  • allows for stretching
  • provides elasticity of loose connective tissues, skin, lungs, and blood vessels
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37
Q

Describe tropoelastins

A
  • soluble precursor to elastin fiber
  • highly extensible
  • molecular nanosprings
  • self-assemble into randomly cross-linked, hydrophobic elastin fibres in the ECM
  • result in an unordered, elastic network
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38
Q

Describe glycosaminoglycans

A
  • gel forming complex polysaccharides
  • regular repeats of disaccharides
  • e.g, Hyaluronan/hyaluronic acid
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39
Q

Describe hyaluronan

A
  • simplest and most abundant GAG
  • 25,000 glucuronic acid & N-acetylglucosamine
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40
Q

Describe Uronic acid

A
  • glucuronic acid
  • galacturonic acid
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41
Q

Describe the properties of GAGs

A
  • usually heavily sulphated: negative charge
  • strongly hydrophilic
  • adopt extended conformations
  • occupy a huge volume relative to their mass
  • inflexible
  • form gels at even low concentrations
42
Q

Describe the effect of the negative charge of GAGs

A
  • attracts sodium
  • osmotic effect increases swelling / turgor pressure
  • enables it to withstand large compressive forces
43
Q

Describe proteoglycans

A
  • gel forming complex polysaccharides
  • GAGs attached to proteins
    via S or T
  • O-linked glycosylation with Glycosaminoglycan (GAG)
  • up to 95% carbohydrate by weight
44
Q

S

45
Q

T

46
Q

Glycan linker and GAG are added in

A

the Golgi apparatus

47
Q

Describe the components of the plant cell wall

A
  • more carbohydrates than proteins
  • fibrils
  • fibril crosslinkers
  • gel
  • synthesised by all plant cells
48
Q

Describe plant cell wall fibrils

A

cellulose polysaccharide micro-crystals

49
Q

Describe plant cell wall fibril crosslinkers

A

Hemicellulose polysaccharide

50
Q

Describe plant cell wall gel

A
  • Pectin polysaccharide
    (-Lignin polyphenolic polymer)
51
Q

Describe cellulose

A
  • polymer of beta(1,4) linked D-glucose
  • forms straight, unbranched polymer chain
  • most abundant biopolymer on Earth
52
Q

Describe cellulose fibres

A
  • 18-24 hydrogen-bonded cellulose polymers form a microfibril
53
Q

microfibril

A
  • micro-crystalline array
  • 24 chains (ca. 3nm)
54
Q

fibril

A

(ca. >20nm)

55
Q

Describe the effect of cellulose’s crystalinity

A
  • insolubility
  • acid resistance
  • high tensile strength (1011 Nm-2)
56
Q

Describe cellulose synthesis

A
  • at the surface of the plasma membrane
  • by multimeric enzymatic terminal complices
  • can be visualised using freeze-fracture electron microscopy of plant plasma membranes
57
Q

terminal complices aka

A

terminal rosettes

58
Q

Terminal rosettes

A
  • contain proteins CESA proteins
  • each rosette has 6 particles
  • each particle has 3-6 CESA proteins
  • 18-24 chains = minimal microfibril
59
Q

CESA

A
  • cellulose synthase A
  • each makes one cellulose polymer
  • sequence similarity to bacterial cellulose synthesis
60
Q

What determines growth direction?

A
  • orientation of cellulose microfibril deposition
  • cell will elongate in a direction perpendicular to the orientation of the cellulose fibrils, between the fibrils
  • orientation of cellulose fibrils can limit the extent of cell growth.
61
Q

Describe cellulose organisation

A
  • needs microtubule reorganisation
  • mutations that disrupt microtubule organisation disrupt cellulose deposition
  • can be viewed under fluorescence and SEM
62
Q

Microtubules guide the deposition of

A
  • cellulose microfibrils
  • no motor proteins needed
  • it is hypothesised that cellulose polymerisation provides the motive force
63
Q

Describe hemicellulose

A
  • network crosslinker
  • glucan backbone
  • meshwork cross-links and separates cellulose fibrils
  • synthesised in the Golgi apparatus
  • transported in secretory vesicles that fuse with the PM
64
Q

Give examples of hemicelluloses

A
  • xyloglucans
  • heteromannans
  • heteroxylans
  • mixed-linkage glucan
65
Q

Describe xyloglucan

A
  • side chains lie along one side of B(1,4) glucose polymer backbone
  • other side can interact with cellulose microfibrils
  • span between cellulose microfibrils
  • act as a ‘glue’ forming mechanical ‘hot-spots’
66
Q

Describe the plant cell wall architecture

A

pectins form an independent gel

67
Q

Describe the pectins

A
  • collective name for a group of closely related acidic polysaccharides
  • gel consistency regulated by Ca2+
  • among the most complex macromolecules in nature (17 different monosaccharides, >20 different linkages)
  • synthesised in the Golgi apparatus and transported in secretory vesicles that fuse with the PM
68
Q

Describe pectin functions

A
  • influence various cell wall properties
  • protect against pathogens
  • much less hygroscopic than GAGs
  • most abundant in the middle lamella (the ‘glue’ between two cells)
69
Q

Which cell wall properties does pectin influence?

A
  • porosity
  • surface charge
  • pH
  • ion balance
70
Q

Describe the effects of having a plant cell wall

A
  • cells can’t move or grow past each other
  • daughter cells conjoined at birth by a shared wall
  • shape of individual organs determined solely by growth vectors of individual cells
  • turgor pressure pushes against the cell wall to maintain cell turgidity
71
Q

How is turgour pressure generated?

A

a central vacuole

72
Q

Describe plant cell growth

A
  • requires carefully regulated loosening of the cell wall
  • stress is imposed by P
  • cell wall has y
  • Rate of expansion is determined by ɸ
73
Q

P

A

turgour pressure

74
Q

y

A
  • yield threshold
  • pressure above
    which the wall yields to pressure
75
Q

ɸ

A

wall extensibility

76
Q

R

A

relative growth rate

77
Q

Lockhart equation

A

R = ɸ(P-Y)

78
Q

Describe plant cell expansion

A

1) increase turgor pressure
2) increase ɸ by loosening fibril crosslinking

79
Q

Describe the acid growth model for loosening cross-links

A
  • apoplastic pH reduced by plant growth hormones
  • cell walls expand more readily below pH5
  • acid growth requires the activity of expansin proteins
80
Q

Name a plant growth hormone

81
Q

Describe the role of expansins

A
  • disrupt hydrogen bonding between cellulose and hemicellulose in ‘mechanical hotspots’
  • reduce pectin rigidity
82
Q

What allows cellulose fibrils to separate

A

Loosening of the ’glue’

83
Q

Describe the Primary Cell Wall

A
  • in relatively young, growing cells
  • flexible, malleable, expandable
  • formed between cells upon division
  • mostly polysaccharide
84
Q

Describe the Secondary Cell Wall

A

– develops once cells reach final size
– greater rigidity
– multi-layered
– resists biological, chemical, and physical attack
- 3 layers with middle lamella

85
Q

Describe the composition of primary plant cell walls

A
  • 90% polysaccharides (30% cellulose, 30% hemicellulose, 30% pectins)
  • 10% proteins
86
Q

Describe the composition of secondary plant cell walls

A
  • 72.5% polysaccharides (65% cellulose, 7.5% hemicellulose)
  • 5% proteins
  • 22.5% lignins
87
Q

How do animal cells interact with the ECM?

88
Q

Describe integrins - the basics

A

cell-surface receptors that mediate cell adhesion to the ECM and to other cells

89
Q

Describe integrins - the specifics

A
  • heterodimeric transmembrane proteins (alpha and beta chains)
  • bind to different ECM components, sometimes via multivalent ECM proteins
  • present at focal adhesions
90
Q

Give an example of multivalent ECM proteins

A

fibronectin

91
Q

Describe the functions of the focal adhesions

A
  • defines cell shape
  • signalling
  • essential for cell migration at the trailing edge
92
Q

Describe signalling at the focal adhesions

A

transduces mechanic and chemical information from outside

93
Q

How does the animal ECM respond to mechanical stress?

A
  • Collagen reorientation by mechanical stress
  • Stress fibers realign to collagen pattern
94
Q

How does the plant ECM respond to mechanical stress?

A
  • microtubule reorientation
  • altered orientation of cellulose deposition
95
Q

Describe the role of the ECM in fibroblast differentiation

A

could go into:
1) osteoblast
2) adipocyte
3) smooth muscle cell
4) chondrocyte

96
Q

chondrocyte

A

cartilage cell

97
Q

Different ECM components are permissive for

A

neuronal outgrowth

98
Q

Describe cell wall integrity signals from the plant cell wall in development

A

Local cell wall loosening at the apical meristem initiates new organ formation

99
Q

Animal ECM and plant cell wall are

A

analogous structures with a similar composition in animals and plants (fibrils, cross-linkers, gel), but different components

100
Q

Summarise the functions of the ECM

A
  • structural, signaling, regulation
  • coordination with cytoskeleton to determine cell shape and
    transduce extracellular information
  • bidirectional regulation between cells and ECM/cell wall
101
Q
  • Coordination with cytoskeleton to determine cell shape and
    transduce extracellular information
  • Bidirectional regulation between cells and ECM/cell wall

Hilary Term 1 (61 decks)

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