BIO 211 Lecture 7: Week 4 class 1

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Cytoskeleton- a system of filaments
o Actin filaments- determine cell shape
Required for locomotion
Role in cell division
o Microtubules- determines position of membrane enclosed organelles
Directs intracellular transport
Forms mitotic spindle
Segregates chromosomes while cells are dividing
o Intermediate filaments- provide mechanical strength
I. Function and Origin of the Cytoskeleton
a. Cytoskeletal Filaments Adapt to Form Dynamic or Stable Structures
i. Cytoskeletal systems- dynamic, adaptable, organized systems
1. Able to quickly adapt
2. Regulation allows binding and assembly of filaments
a. Actin filaments- underlie the plasma membrane
i. Provides shape and strength
ii. Forms cell-surface projections
iii. Lamellipodia and filopodia allows movement
b. Microtubules- in cytoplasmic arrays that extend to the
cell's periphery
i. Rearrange to form mitotic spindle
ii. Form cilia- sensory devices/ tracks for transport
c. Intermediate filaments- line inner face of nuclear
envelope
i. Provides protection for DNA
ii. Twisted into cables in the cytosol
1. Hold epithelial cells together
2. Helps nerves extend axons
iii. Form tough appendages (hair)
ii. Important for cells to organize quickly during cell division
1. Mitotic spindles segregates chromosomes
2. Actin allows cells to change shape and move
a. Myosin forms a belt around the middle of the cell--->
contractile ring- constricts to pinch cell into 2
b. The Cytoskeleton Determines Cellular Organization and Polarity
i. Cells with a differentiated morphology must still have a stable
cytoskeleton
1. Epithelial cells
a. Microvilli and cilia remain constant through the cell's
entire life
i. Actin must be replaced to remain stable
ii. Cytoskeleton determines a cell's polarity
1. All filaments are involved in establishing a difference
between apical and basolateral surface of a cell
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