PSYC 211 Study Guide - Final Guide: Securin, Cyclin-Dependent Kinase 1, Nuclear Membrane

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11 Aug 2016
BIOL 201 – Cell Biology and Metabolism C. Aikins
Notes II: Topic 11 - 15 (Cell Cycle) Winter 2011
Topic 11 – Introduction to the Cytoskeleton and Actin
Cells come in many shapes
Ex. muscle cells are long, cylindrical, multi-nucleated cells
Epithelial cells come in different shapes and sizes
Simple columnar, simple squamous, transitional, stratified squamous (thin, flattened cells)
With the same genetic information, different cells are able to adopt significantly different shapes
Cell has a large degree of internal organization
Apical domains often different from the basolateral domains
Apical domain interacts with the lumen of an organ
Basolateral domain communicates with the extracellular matrix
Cells can import and export cargo
Cytoplasmic dynein (bring towards centre), Kinesin family member (move away)
Cells can move
In contrast, bacteria and amoeba swim
Cell constructs its own polymerized cytoskeleton to allow for organization and motility
Made up of microfilaments (actin filaments), microtubules and intermediate filaments
Lots of diseases associated with intermediate filaments, but there is significantly less known about them (tough to
Cells can control the shape of the cytoskeleton
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Roles of the Cytoskeleton
Provide shape, structure and stability
If a nerve wants to make a new connection with a neighbouring neuron, will extend itself towards the neuron by
extending its cytoskeleton
Initiated by extension of the actin filaments, followed by the microtubules
Intracellular transport
Provides a ‘highway’ for organisms and substances within the cell
Contractility and motility
Allows muscle cells to contract (cells that were long and skinny become short and fat)
Spatial Organization
Polymers of the Cytoskeleton
Cells produce small proteins that have the ability to self–associate, polymerizing into long rods
resistant to compression
Important for intracellular transport and in cell division
Actin Filaments
high tensile strength
but flexible
Two proto-filaments of actin coil around in each in a helix, forming the actin filament
Intermediate filaments
elastic and flexible
When considering an analogy to scaffolds, the microtubules are the poles
Very stiff and resistant to compression (will buckle eventually)
Actin filaments are the wires
Have a high tensile strength, yet flexible as the same time
Intermediate filaments are the ropes
Both elastic and flexible (monomers can slide)
Actin is an ATPase
Has an ATP-binding cleft in its core
Binding of ATP is critical for the polymerization of actin
Actin is the leading force for movement, with ATP driving it
The helix of an actin filament has a periodicity is 36nm
The filament is polar such that it has two distinct polar ends
(+) end or barbed end and a (-) end
Movement and polymerization occur at specific ends
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Actin is one of the most common proteins in your body, especially motile ones
Actin Localization:
Microvilli cell protrusions made from actin filaments all oriented in the same direction
Paralleled, bundled array of actin
Line epithelial cells
Cell cortex a layer of cross-linked actin filaments that sits immediately below
the plasma membrane in all cells
“actin cage” that underlines the plasma membrane
Area of active contemporary research
While secreting, must pass through this cell cortex (such as during
Stress fibres actin cables within a cell (parallel bundles)
Filopodia actin spikes stretching from the cell to make contact with a
Parallel bundles
Lamellipodium/leading edge at the leading edge of the cell underlying cell
Cross-linked network called a dendritic network of actin filaments
Contractile ring formed during cytokenesis
Before movement, a cell is stuck to a surface by focal adhesion (stuck via rigid
Extension lamellipodium (actin-rich cellular protrusion) shoots out in direction of movement
Cell orients itself using the different directions of the action fibres
At the leading edge, actin filaments are growing to form a cross-linked network that pushes the membrane out
New actin monomers must migrate to the cell membrane to be added to the extending actin filaments
Adhesion lamellipodium forms a new adhesion with the surface
Translocation actin stress fibres and cables pull the body of the cell forward
De-adhesion and endocytic recycling old adhesion is released
Draw moving cell! Mar 4th lect
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