Cytoskeleton of Cell0
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Transcript of Cytoskeleton of Cell0
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CYTOSKELETON OF CELL
Cytoskeleton - network of tiny protein fibres in cytoplasm
- Provides shape and support to cell
- Involved in movement of organelles and sometimes the cell itself
-certain cells only
- Can be dismantled and reassembled as required.
Three types of cytoskeleton fibres
Microtubules Intermediate Microfilaments
Filaments
largest smallest
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Microtubules
-Tiny hollow rods of variable length made of proteins called tubulins
[ 25nm in diameter]
Can be assembled and disassembled in cell as needed
Usually grow from region of cell called centrosome
Centrosome also contains a pair ofcentrioles (animals only) = barrel
shaped rings of microtubules
Two centrioles always at right angles to each other
Microtubule functions
- Cell support - Act as girders supporting cell and giving it shape
- Act as tracts along which small organelles move.
- During cell division centrosome produces spindle apparatus made ofmicrotubules along which chromosomes move
- Form cilia and flagella may cause movement of cell
CILLIA: Short hair like projections from surface of cell. A cell has many
cilia which beat in unison.
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FLAGELLA: long whip like extension of cell 1-2 per cell - cause
movement of cell.
CILIA
Unicellular organisms Man
Movement of cell movement of fluid
over surface of cell
eg paramecium eg Trachea [windpipe]
FLAGELLA
Unicellular organisms Sperm of many Animals + man
Cilia and Flagella - Structure identical
Each made of a ring of 9 pairs of microtubules ( fused) with 2 in centre .
Covered with plasma membrane.
= 9+2 pattern
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(a) cilium showing 9+2 pattern and basal body
Cilia and flagella are anchored to cell by basal body - structure identical tocentriole - 9 triplets of microtubules
Movement caused by tiny arms attached to microtubule pairs dynein arms
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MICROFILAMENTS
Smallest of cytoskeleton fibres
Made from actin proteins which form 2 strands which twist around each
other
can be assembled and disassembled as required
Functions
- Maintenance of cell shape and structures such as microvilli
- Changes of cell shape including formation of pseudopodia (cellextensions).
- Division of cell in two in animals.
- Essential for muscle contraction - with thicker myosin filaments
INTERMEDIATE FILAMENTS
Form more permanent framework providing shape
to cell- are not assembled or disassembled
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Made of different keratin proteins coiled together
Function
- Provide shape to cell
- Anchor certain organelles in place
eg Nucleus sits in cage of intermediate filaments
- Axons of neurons strengthened by intermediate filaments
- Forms nuclear lamina
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CELL JUNCTIONS
Human cells can have 3 types of intercellular junctions
tight junctions desmosomes gap junctions
Not all cells have junctions between them.- common in tissues such as
epithelium and muscle tissue
Tight junctions [Form seal]
Membranes of neighbouring cells are fused at the junction forming a seal
that prevents leakage between cells
Form continuous belts around cell eg intestine
Desmosomes [ anchoring ] junctions
Function like rivets holding cells together
Get circular plaques or discs on inside of each membrane. Also appear to
be protein filaments between cells which extend into cell on either side
plaques are reinforced by keratin fibres in cell
Gap Junctions
Provide communication between cells
Eg muscle cells, gland cells, embryos
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-Tiny cell to cell channels made of special membrane proteins
-Channels permit ions, nutrients, some hormones and electric signals to
pass through.