BIO130 Section 2 Lecture 9 and 10.docx

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14 Apr 2012
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Lecture 9 and 10: Interactions b/w cells and their environments. How cells interact to build tissues
- Microvillus of epithelial cells increase SA and allow intake from intestine
- Mechanical stresses are transmitted from cell to cell by cytoskeleton filaments anchored to cell matrix and cell-
cell adhesion site. Extracellular matrix directed bears mechanical stresses of tension and compression
- 2 main types of tissues:
o Epithelial tissue: (cells polar) eg. Intestinal lining, skin epidermis
Cells closely associated to each other
Limited ECM (a thin basal lamina that underlies the basal domain
Cytoskeletal filaments provide resistance to mechanical stress
Cells are attached to each other by cell junctions
o Connective tissue: eg. Bone, tendon
Cells are rarely connected to each other
Plentiful ECM which provides resistance to mechanical stress. Cells generally surrounded by
ECM (not polar)
cells are attached to ECM
- different types of junctions b/w cells:
o anchoring junctions (epithelial cells): anchor cells to each other, allow cytoskeletal filaments from one
cell to connect to other. Allow junction to ECM
o occluding junctions (epithelial cells): tight junctions which link epithelial cells to each other and prevent
transfer of materials b/w cells (creates separation b/w intestinal lumen domain and ECF of basal
domain) tight junctions also prevent mixing of proteins from apical and basal side
o channel-forming junctions (epithelial cells): allow communication b/w cells. Coordinated cells.
o signal-relaying junctions: eg. synapse. Signals are transferred
- in polarized epithelial cells: junctions are arranged in a specific order
o occulding tight junction seals gap b/w epithelial cells and prevent mixing
o adherens junction connects actin filaments bundle in one cell with that in the next cell and hold tight
junctions in place
o desmosome connects intermediate filaments in one cell to those in next cell and provide the most
mechanical support (prevents tearing of sheet)
o channel-forming junctions: gap junction allows the passage of small water soluble molecules from cell to
cell
o cell matrix anchoring junctions:
hemidesmosome anchors intermediate filaments in cell to extracellular matrix
actin linked cell matrix adhesion anchors actin filaments in cell to extracellular matrix
- tight junctions: create tight seal b/w cells prevent mixing of Extracellular environment. Allows specific cells to
flow (regulated)
o acts as fences in membrane prevent mixing of membrane proteins
apical membrane proteins (need sodium glucose symporter)
basal membrane proteins (GLUT Uniporter)
- epithelial sheets are a barrier
- tight junctions are made up of 2 types of proteins: claudin and occludin form seal which brings 2 membranes
together and make tight barrier
o Transmembrane proteins:
o Extracellular loop domains: interact w/ extracellular domains of proteins in neighboring cell; occludin of
one cell interacts with occludin of other cell; claudin with claudin. Protein interacts form pintches in
membrane
o Claudin: required for tight junction seals. Functional proteins are required in both cells
More important (tested by deletion from cells)
- Several sealing strands wrap around the perimeter of the cell creating a seal (tight junction)
o PM of adjacent cells are brought close together at sealing stand and held together by interaction of
proteins
o There are some molecules are able to pass through (eg Mg able to pass through in kidney therefore
prevented from being excreted in urine) SELECTIVELY PERMEABLE BARRIER
- Tight junctions are dependent on adherens junctions
o If you block the formation of adherens junctions b/w cells, tight junctions don’t form properly
- Anchoring Junctions
o Cell-cell anchoring junctions
o Cell-matrix anchoring junctions
o Link the cytoskeletons of neighboring cells
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