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BIO130 Section Two Guide (5)

17 Pages
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Department
Biology
Course Code
BIO130H1
Professor
Kenneth Yip

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Cell Junctions, Cell Adhesion, and the Extracellular Matrix
Cohesion is mandatory to form an organized multicellular structure
oGoverns the bodys shape, strength and the arrangement of its different cell
types
Junctions between cells create pathways for communication
Attachment to other cells and to the ECM control the orientation of each cells
internal structure
oThe making and breaking of these attachments and the modeling of the
matrix governs the way cells move within the organism, guiding them as the
body grows
Defects within the cell junction, adhesion and ECM can lead to various diseases
How can cells combine into millions and form a massive structure like a
tree or horse? Two basic building strategies:
oDepends on the strength of the ECM:
Complex network of proteins and polysaccharide chains that cell
secrete
oDepends on the strength of the cytoskeleton inside the cells and on cell-cell
adhesions:
These adhesions tie the cytoskeletons of neighbouring cells together
ECM in plants are important
plant tissues owe their strength to the cell
walls that surround each cell
For animals, both structures are used for different purposes and different
tissues
Animal tissues fall into two categories: connective and epithelial
oConnective:
E.g., bone or tendon
A lot of ECM cells are sparsely distributed within it
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The rich matrix is fibrous in polymers (especially collagen) and also
bears the most of the mechanical stress to which the tissue is
subjected
Direct attachments from one cell to another cell is rare
oEpithelial:
E.g., lining of gut or the epidermal covering of the skin
Cells are closely bound together into sheets called epithelia
ECM is scanty consists mainly of basil lamina
Physical attachment is critical in both epithelial and non-epithelial tissues
Junctions between cell and cell or between cells and matrix are diverse in structure
and have four main functions:
Junction TypeDefinition Classification
Anchoring (including both cell-cell
adhesions and cell-matrix
adhesions), transmit stresses
and are tethered to
cytoskeletal filaments inside
the cell
Actin filament attachment
sites:
1. cell-cell junctions
(adherens junctions)
2.cell-matrix junctions
(actin-linked cell-matrix
adhesions)
Intermediate filament
attachment sites:
1. cell-cell junctions
(desmosomes)
2. cell-matrix junctions
(hemidesomosomes)
Occluding Seal the gaps between cells
in epithelia so as to make
the cell sheet into an
impermeable (or selectively
permeable) barrier
1. tight junctions (in
vertebrates)
2.septate junctions (in
invertebrates)
Channel-forming Create passageways linking
the cytoplasms of adjacent
cells
1. gap junctions (animals)
2.plasmodesmata (in plants)
Signal-relaying Allow signals to be relayed 1. chemical synapses
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from cell to cell across their
plasma membranes at sites
of cell-to-cell contact
(nervous system)
2.immunlogical synapses
(immune system)
3. transmembrane ligand-
receptor cell-cell signalling
contacts.* Anchoring,
occluding and channel-
forming junctions can all
have signalling functions
in addition to their
structural roles.*
Cadherins and Cell-Cell Adhesion
Structures of cell-cell adhesion is clearly seen in mature epithelia and some other
tissues (e.g., heart muscle) that are held together be strong direct anchorage of cell
to cell
Adherens junctions anchorage sites for actin filaments
Desmosome junctions anchorage sites for intermediate filaments
oMingled with these junctions are the channel-forming junctions gap
junctions
At each four types of anchoring junctions, the central role is played by
transmembrane adhesion proteins one end links to the cytoskeleton inside
the cell and the other end linking to other structures outside has two
superfamilies:
oCadherin:
Mediate attachment of cell to cell
oIntegrin:
Mediate attachment of cells to matrix
Some cadherins link to actin and form adherens junctions, while others link to
intermediate filaments and form desomsome junctions
Some integrins link with actin and form actin-linked cell-matrix adhesions, while
others link to intermediate filaments and form hemidesomosomes
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Description
Cell Junctions, Cell Adhesion, and the Extracellular Matrix Cohesion is mandatory to form an organized multicellular structure o Governs the bodys shape, strength and the arrangement of its different cell types Junctions between cells create pathways for communication Attachment to other cells and to the ECM control the orientation of each cells internal structure o The making and breaking of these attachments and the modeling of the matrix governs the way cells move within the organism, guiding them as the body grows Defects within the cell junction, adhesion and ECM can lead to various diseases How can cells combine into millions and form a massive structure like a tree or horse? Two basic building strategies: o Depends on the strength of the ECM: Complex network of proteins and polysaccharide chains that cell secrete o Depends on the strength of the cytoskeleton inside the cells and on cell-cell adhesions: These adhesions tie the cytoskeletons of neighbouring cells together ECM in plants are important plant tissues owe their strength to the cell walls that surround each cell For animals, both structures are used for different purposes and different tissues Animal tissues fall into two categoriecs:nnectiveand epithelial o Connective : E.g., bone or tendon A lot of ECM cells are sparsely distributed within it www.notesolution.com The rich matrix is fibrous in polymers (especially collagen) and also bears the most of the mechanical stress to which the tissue is subjected Direct attachments from one cell to another cell is rare o Epithelial: E.g., lining of gut or the epidermal covering of the skin Cells are closely bound together into sheets caellp eidthelia ECM is scanty consists mainly ob fasil lamina Physical attachment is critical in both epithelial and non-epithelial tissues Junctions between cell and cell or between cells and matrix are diverse in structure and have four main functions: Junction Type Definition Classification Anchoring (including both cell-cell Actin filament attachment adhesions and cell-matrix sites: adhesions), transmit stresses1. cell-cell junctions and are tethered to (adherens junctions) cytoskeletal filaments inside 2.cell-matrix junctions the cell (actin-linked cell-matrix adhesions) Intermediate filament attachment sites: 1. cell-cell junctions (desmosomes) 2. cell-matrix junctions (hemidesomosomes) Occluding Seal the gaps between cells 1. tight junctions (in in epithelia so as to make vertebrates) the cell sheet into an 2.septate junctions (in impermeable (or selectively invertebrates) permeable) barrier Channel-forming Create passageways linking 1. gap junctions (animals) the cytoplasms of adjacent 2.plasmodesmata (in plants) cells Signal-relaying Allow signals to be relayed 1. chemical synapses www.notesolution.com
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