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Cells, organisms and systems > 4.4 - Cell communities/connections > Flashcards

4.4 - Cell communities/connections Flashcards

1
Q

role of extracellular matrix on shaping cells (2)

A
  1. cell-cell and cell-extracellular matrix interactions control cell shape/function and determine developmental fate of cells/tissues
  2. cell-adhesion molecules mediate cell-cell adhesion, receptors mediate cell-matrix adhesions
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2
Q

what does the extracellular matrix consist of?

A

complex meshwork of proteins and polysaccharides that contribute to tissue structure and function

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3
Q

2 main polysaccharide components of plant cell wall (2)

A
  1. cellulose (predominant)
  2. pectin
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4
Q

plant cell wall structure (2)

A
  1. arranged in layers on extracellular side of plasma membrane
  2. cellulose forms matrix with other polysaccharides and structural proteins to form structure that resists compression and tension
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5
Q

cellulose (2)

A
  1. carbohydrate polymer of glucose
  2. very tough and water impermeable
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6
Q

whats unusual about cellulose synthesis in plant cells?

A

synthesised on surface of cell (by cellulose synthase embedded in the membrane)

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7
Q

microtubule role in cellulose synthesis

A

microtubules serve as guides to orient movement of cellulose synthase complex

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8
Q

what influences the direction in which a plant cell elongates under turgor pressure (internal water pressure)

A

orientation of cellulose microfibrils within the plant cell wall
(cell tends to elongate in direction perpendicular to orientation of microfibrils, great tensile strength)

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9
Q

plasmodesmata (3)

A
  1. intercytoplasmic channels of plasmodesmata pierce plant cell walls, connecting cytoplasms of all cells in plant
  2. each plasmodesmata lined with plasma membrane common to the 2 connected cells (usually contains fine tubular structure - desmotubule)
  3. derived from smooth ER
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10
Q

what forms bulk of connective tissues in animal cells

A

extracellular matrix (no cell wall)

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11
Q

what are the names of cells that produce extra cellular matrix in connective tissues? (2)

A
  1. in most tissues - fibroblast
  2. in bones - osteoblasts
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12
Q

key components of of extra cellular matrix in animals (2)

A
  1. collagen
  2. proteoglycans
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13
Q

collagen (2)

A
  1. animal version of cellulose
  2. composed of peptides (not polysaccharides)
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14
Q

proteoglycans (2)

A
  1. carbohydrates with protein component that have charged residues which attract water
  2. allows ECM to function bit like gel
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15
Q

where is collagen found? (2)

A
  • most abundant protein in animals
    1. skin
    2. connective tissues etc
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16
Q

collagen structure (3)

A
  1. 3 intertwined helical polypeptide chains
  2. a-helices stabilised by steric repulsion of proline rings (not H-bonds)
  3. striated appearance - only glycine can fit in interior, spaced every 3 residues
17
Q

collagen fibrils (3)

A
  1. many rodlike collagen molecules covalently cross-linked in intracellular space
  2. 3 intertwined chains also interact via H-bonds
  3. gives collagen fibrils tensile strength greater than steel
18
Q

collagen organisation in skin

A

collagen fibrils organised into sheets oriented in different directions to resist tensile strength in different directions

19
Q

collagen organisation in cells (principally fibroblasts)

A

achieve organisation by moving around intercellular spaces laying down collagen in oriented fashion then reshaping it

20
Q

how can collagen be post-translationally modified and what is the enzyme/cofactor? (2)

A
  1. hydroxylation of proline and lysine
  2. catalysed by prolyl hydroxylase, requires ascorbate (vitamin C) as cofactor
21
Q

integrins (adaptor proteins linking cytoskeleton to ECM)

A

transmembrane proteins bind to actin cytoskeleton in cytoplasm and to extra cellular matrix proteins via fibronectin

22
Q

fibronectin

A

binds to actin cytoskeleton and collagen making link between cytoskeleton and extra cellular matrix

23
Q

epithelia

A

majority of cell types organised into multicellular sheets of cells joined together side by side to form a barrier

24
Q

where do epithelia cover?

A

external surface of a body and line internal cavities

25
Q

how does epithelia contrast connective tissue?

A

primarily carries mechanical load through cell-cell connections and cytoskeleton (connective tissues use extra cellular matrix)

26
Q

2 faces of epithelial cells (2)

A
  1. apical face - free and exposed to outside
  2. basal face - rests on sheet of connective tissue
27
Q

basal lamina

A

lies between basal face and underlying connective tissue, specialised ECM layer to which the cells are attached

28
Q

tight junctions (2)

A
  1. seel neighbouring cells together in epithelial sheet (prevents leakage of molecules between them)
  2. formed from proteins (claudins and occludins) arranged in strands along lines of junction
29
Q

desmosomes (3)

A
  1. join intermediate filaments (keratin) between cells (prevents cells ripping apart under mechanical stress)
  2. built around proteins of cadherin family (nucleate a cytoplasmic plaque anchoring intermediate filaments)
  3. leads to great tensile strength in sheet (skin epidermis)
    - hemidesmosomes = similar but connect cells to basement membrane
30
Q

gap junctions (3)

A
  1. provide neighbouring cells with direct channel of intercytosolic communication (allows passage of small water soluble ions/molecules)
  2. 2 opposing plasma membranes linked by protein assemblies (connexons)
  3. 2 connexons join across intercellular gap - forms aqueous channel connecting cytoplasms of 2 cells
31
Q

adherens junctions (2)

A
  1. join actin bundle in one cell to actin bundle in another (allowing contractile movements)
  2. contraction of actin filament causes layer to roll - leads to tube-like structures even spheres (crucial during embryo development)
32
Q

effect of contraction of apical bundles of actin filaments linked from cell to cell via adherens (2)

A
  1. causes epithelial cells to contract at their apex
  2. depending on orientation causes epithelial sheet to invaginate or roll up into tube
33
Q

animal cell junctions (4)

A
  1. tight junctions
  2. desmosomes
  3. gap junctions
  4. adherens junctions
34
Q

main function of tight junctions

A

prevent leakage of cells in epithelial sheets

35
Q

main function of desmosomes

A

provides tensile strength and prevents cells from ripping under mechanical stress

36
Q

main function of gap junctions

A

allows passage of small water soluble ions and molecules between cells

37
Q

main function of adherens junctions

A

allows contractile movement of cells

Cells, organisms and systems (26 decks)

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