Download AP Biology Gap Junctions

Cell-Cell
Interactions
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Tissues
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Levels of Organization
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Cells stick together to form tissue
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Levels of Organization
 How do individual cells “connect” to
form tissue?
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Interactions between cells
Gap junction
Desmosome
Tight junction
Which is anchoring and why?
Which is involved in permeability between cells and how is that permeability mediated?
Which is a communication junction?
Which is most similar to the plasmodesmata (in plants) and why?
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Transport across membranes
 Plasma membranes
can join together to
form tight junctions
 Adherens junctions
membranes
“glued” together by
proteins
- pass through both
membranes and attach
to cytoskeletons
 Desmosomes
proteins “button”
two membranes
together
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Tight Junctions
 Zonulae Occludens
 forms a band completely around

the cell fusing cells together and
closing off intercellular space
Fusion site #
often correlates to “leakiness”
Fewer fusion sites  greater
permeability to water and solutes
More fusion sites  less permeable…
In what
How would the #
organs would you
Of fusion sites
expect
Affect permeability?
few fusion sites?
Cells of the proximal renal tubule of the kidney where filtration often takes place have few
fusion sites to allow for leakability, whereas, cells of the urinary bladder (that must hold
urine and not allow it to leak out) contains numerous fusion sites or tight junctions to form
a seal to prevent the flow of materials between epithelial cells.
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Tight Junctions
 Proteins interact
to form tight
junctions
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You do not need to know these specific proteins.
Gap Junctions
 A gap between neighboring cell membranes
 Gap Junction (communicating junction)
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Gap Junctions
Connexin surrounds the pore,
- acts like a hydrophilic ion channel between cells
 Individual unit of the gap junction = connexon
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Desmosome
 Anchoring junctions
 Does not surround cell
 Adhesion is strengthened by
intermediate filaments (keratin)
 Hemidesmosome = half a desmosome
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Plant Cell Wall
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Plasmodesmata
 Intercellular connections between
adjacent plant cells
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Plasmodesmata
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Summary
 Adhering junctions:

Desmosome & hemidesmosome
 Impermeable junctions:

Tight junctions
 Communicating junctions:

Gap junctions (and in plants, plasmodesmata)
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