Transcript Cell Surfaces and Junctions

Cell Surfaces and Junctions
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Presentation to environment
Defense mechanisms
Maintain Structure
Allow communication between cells
Plant Cell Walls
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Flexible primary wall is later reinforced by more rigid secondary walls
Area between cells is filled with Middle lamella
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Contains pectin which is a sticky gelatinous molecules
Plasmodesmata are channels between cells that allow cytoplasm exchange
Fig. 6-28
Secondary
cell wall
Primary
cell wall
Middle
lamella
1 µm
Central vacuole
Cytosol
Plasma membrane
Plant cell walls
Plasmodesmata
Extracellular matrix
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Many types of glycoproteins
Proteoglycans are more carbohydrate than
protein
 Form branched complexes
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Fibronectins act as docking site
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Bound to Integrins
Integrins span membrane and are bound to
cytoskeleton
Fig. 6-30
Collagen
Proteoglycan
complex
EXTRACELLULAR FLUID
Polysaccharide
molecule
Carbohydrates
Fibronectin
Core
protein
Integrins
Proteoglycan
molecule
Plasma
membrane
Proteoglycan complex
Microfilaments
CYTOPLASM
Role of ECM
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Gives tissue stability by linking areas of cells
together
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Allows communication between cells
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Like cargo net
Fibronectin and integrins are involved in signal
sending and receiving
ECM is essential in development
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Provide landmarks for extending structures
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Neurons and vascular tissue
Intercellular junctions
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Tight junctions connect cells together and block of “seepage” of
extracellular fluids
Desmosomes anchor adjacent cells together structurally
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Linked to Intermediate filaments
Gap junctions allow molecules to pass from cell to cell
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Comparable to plasmodesmata in plants
Fig. 6-32
Tight junction
Tight junctions prevent
fluid from moving
across a layer of cells
0.5 µm
Tight junction
Intermediate
filaments
Desmosome
Gap
junctions
Space
between
cells
Plasma membranes
of adjacent cells
Desmosome
1 µm
Extracellular
matrix
Gap junction
0.1 µm
Overview of cell revisited
Emergent properties
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Something extra that makes the whole greater
than the sum of the parts
In cells the coordinated interaction between
organelles and the regulation of
cellular/molecular events
At the tissue level the cell surfaces and
junctions allow communications and
coordination of a larger scope