Lecture 5 Flashcards
What is the function of the cytoskeleton?
It allows movement, organization, and gives shape to the cell and organelles
What are the three filament types in the cytoskeleton?
Microfilaments, intermediate filaments, and microtubules
What are some subcellular structures that microfilaments organize into?
Microvilli, cell cortex, adherens belts, stress fibres, and contractile rings
What are microfilaments made of?
Actin monomers
What are the two states of actin?
G-actin (globular) and F-actin (filaments)
What occurs at the (-) end and the (+) end of an actin filament?
Depolymerization occurs at the (-) end and polymerization occurs at the (+) end
What does ATP bound actin favor?
Polymerization
What is the rate limiting step of actin polymerization?
Nucleation
What is a steady state?
When polymerization = depolymerization due to the concentrations of G-actin and F-actin being at equilibrium
How does the treadmilling of microfilaments generate force in the cell?
Treadmilling means that the microfilament is not changing in length, but it is moving in one direction. This movement is what generates the force.
What are actin sequestering proteins?
Proteins that bind at actin to prevent spontaneous polymerization.
What is profilin?
It enhances the loss of ADP off G-actin to increase the concentration of ATP-G actin
What is cofilin?
It binds to ADP-F actin and increases destabilization
What are myosins?
Myosins are ATP dependant proteins that can bind actin, undergo a conformational change, and move against the rigid actin CSK
What do all myosins contain?
An actin binding head domain, a flexible neck, and a tail domain
What does a myosin head domain bind to?
Actin and ATP
What does a myosin tail domain bind to?
Cargo
Where are microtubules anchored?
MTOC (centriole)
Which end of the microtubule anchors in the MTOC?
The negative end
Where are the positive ends of microtubules found?
Near the edges of the cell
What is Gamma-TURC?
It is the nucleation site for microtubules
How do microtubules facilitate CSK-based movement?
By constantly assembling and dissassembling themselves to generate force in a particular direction
Which has a greater role in cellular movement: microtubules or microfilaments?
The treadmilling of microtubules
What does catastrophe refer to?
The rapid disassembly of microtubules when GTPase activity catches up with the polymerization
What are the two motors that are associated with microtubules?
Kinesins and dyneins
What is the major difference between kinesin and dynein?
Kinesin is a (+) end directed motor and dynein is a (-) end directed motor
How do kinesins move?
Via hand-over-hand movement
How do dyneins move?
A power stroke that involves the rotation around the head domain
What is the function of intermediate filaments in the nuclear lamina?
It forms a meshwork on the inner surface of the nuclear envelope that provides structural support to the nucleus
