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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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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

Transport across membranes

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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.

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…

How would the # Of fusion sites

Affect permeability?

In what organs would you

expect few fusion sites?

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Tight Junctions Proteins interact

to form tight

junctions

You do not need to know these specific proteins.

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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)