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

Animal extracellular matrix and plant cell wall Flashcards

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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
Describe collagen
- 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
26
Describe the effect of the amino acid composition of collagen
lends stability to the helix
27
Describe collagen biosynthesis
- 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
28
Collagen helices are cross-linked at
- specific, regular positions - can be viewed under SEM
29
Describe the crosslinkers
- 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
30
Describe network-forming collagen
- assemble into a triple helix with non-helical breaks - introduces flexibility into the molecule
31
Describe Type IV collagen
self-assemble into a sheet-like meshwork to help form basal laminae
32
Describe basal laminae
- 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
33
Describe the basal lamina in muscle cells
- connects to the connective tissue - surrounded by the PM
34
Describe the basal lamina in epithelial sheets
- connected to connective tissue - lumen
35
Describe the basal lamina in the kidney glomerulus
- connects to endothelial cells - epithelial cells
36
Describe elastin
- allows for stretching - provides elasticity of loose connective tissues, skin, lungs, and blood vessels
37
Describe tropoelastins
- 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
38
Describe glycosaminoglycans
- gel forming complex polysaccharides - regular repeats of disaccharides - e.g, Hyaluronan/hyaluronic acid
39
Describe hyaluronan
- simplest and most abundant GAG - 25,000 glucuronic acid & N-acetylglucosamine
40
Describe Uronic acid
- glucuronic acid - galacturonic acid
41
Describe the properties of GAGs
- 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
Describe the effect of the negative charge of GAGs
- attracts sodium - osmotic effect increases swelling / turgor pressure - enables it to withstand large compressive forces
43
Describe proteoglycans
- 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
S
serine
45
T
threonine
46
Glycan linker and GAG are added in
the Golgi apparatus
47
Describe the components of the plant cell wall
- more carbohydrates than proteins - fibrils - fibril crosslinkers - gel - synthesised by all plant cells
48
Describe plant cell wall fibrils
cellulose polysaccharide micro-crystals
49
Describe plant cell wall fibril crosslinkers
Hemicellulose polysaccharide
50
Describe plant cell wall gel
- Pectin polysaccharide (-Lignin polyphenolic polymer)
51
Describe cellulose
- polymer of beta(1,4) linked D-glucose - forms straight, unbranched polymer chain - most abundant biopolymer on Earth
52
Describe cellulose fibres
- 18-24 hydrogen-bonded cellulose polymers form a microfibril
53
microfibril
- micro-crystalline array - 24 chains (ca. 3nm)
54
fibril
(ca. >20nm)
55
Describe the effect of cellulose's crystalinity
- insolubility - acid resistance - high tensile strength (1011 Nm-2)
56
Describe cellulose synthesis
- 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
terminal complices aka
terminal rosettes
58
Terminal rosettes
- contain proteins CESA proteins - each rosette has 6 particles - each particle has 3-6 CESA proteins - 18-24 chains = minimal microfibril
59
CESA
- cellulose synthase A - each makes one cellulose polymer - sequence similarity to bacterial cellulose synthesis
60
What determines growth direction?
- 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
Describe cellulose organisation
- needs microtubule reorganisation - mutations that disrupt microtubule organisation disrupt cellulose deposition - can be viewed under fluorescence and SEM
62
Microtubules guide the deposition of
- cellulose microfibrils - no motor proteins needed - it is hypothesised that cellulose polymerisation provides the motive force
63
Describe hemicellulose
- 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
Give examples of hemicelluloses
- xyloglucans - heteromannans - heteroxylans - mixed-linkage glucan
65
Describe xyloglucan
- 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
Describe the plant cell wall architecture
pectins form an independent gel
67
Describe the pectins
- 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
Describe pectin functions
- 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
Which cell wall properties does pectin influence?
- porosity - surface charge - pH - ion balance
70
Describe the effects of having a plant cell wall
- 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
How is turgour pressure generated?
a central vacuole
72
Describe plant cell growth
- 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
P
turgour pressure
74
y
- yield threshold - pressure above which the wall yields to pressure
75
ɸ
wall extensibility
76
R
relative growth rate
77
Lockhart equation
R = ɸ(P-Y)
78
Describe plant cell expansion
1) increase turgor pressure 2) increase ɸ by loosening fibril crosslinking
79
Describe the acid growth model for loosening cross-links
- apoplastic pH reduced by plant growth hormones - cell walls expand more readily below pH5 - acid growth requires the activity of expansin proteins
80
Name a plant growth hormone
auxin
81
Describe the role of expansins
- disrupt hydrogen bonding between cellulose and hemicellulose in ‘mechanical hotspots’ - reduce pectin rigidity
82
What allows cellulose fibrils to separate
Loosening of the ’glue'
83
Describe the Primary Cell Wall
- in relatively young, growing cells - flexible, malleable, expandable - formed between cells upon division - mostly polysaccharide
84
Describe the Secondary Cell Wall
– develops once cells reach final size – greater rigidity – multi-layered – resists biological, chemical, and physical attack - 3 layers with middle lamella
85
Describe the composition of primary plant cell walls
- 90% polysaccharides (30% cellulose, 30% hemicellulose, 30% pectins) - 10% proteins
86
Describe the composition of secondary plant cell walls
- 72.5% polysaccharides (65% cellulose, 7.5% hemicellulose) - 5% proteins - 22.5% lignins
87
How do animal cells interact with the ECM?
Integrins
88
Describe integrins - the basics
cell-surface receptors that mediate cell adhesion to the ECM and to other cells
89
Describe integrins - the specifics
- heterodimeric transmembrane proteins (alpha and beta chains) - bind to different ECM components, sometimes via multivalent ECM proteins - present at focal adhesions
90
Give an example of multivalent ECM proteins
fibronectin
91
Describe the functions of the focal adhesions
- defines cell shape - signalling - essential for cell migration at the trailing edge
92
Describe signalling at the focal adhesions
transduces mechanic and chemical information from outside
93
How does the animal ECM respond to mechanical stress?
- Collagen reorientation by mechanical stress - Stress fibers realign to collagen pattern
94
How does the plant ECM respond to mechanical stress?
- microtubule reorientation - altered orientation of cellulose deposition
95
Describe the role of the ECM in fibroblast differentiation
could go into: 1) osteoblast 2) adipocyte 3) smooth muscle cell 4) chondrocyte
96
chondrocyte
cartilage cell
97
Different ECM components are permissive for
neuronal outgrowth
98
Describe cell wall integrity signals from the plant cell wall in development
Local cell wall loosening at the apical meristem initiates new organ formation
99
Animal ECM and plant cell wall are
analogous structures with a similar composition in animals and plants (fibrils, cross-linkers, gel), but different components
100
Summarise the functions of the ECM
- structural, signaling, regulation - coordination with cytoskeleton to determine cell shape and transduce extracellular information - bidirectional regulation between cells and ECM/cell wall
101
* 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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