Lecture 17 Flashcards
What are the Three types of cytoskeletal filaments:?
A) Microtubules
B) Microfilaments/Actin filaments
C) Intermediate filaments
What are functions of the cytoskeleton?
Structural role
Motility
Cell division
Signaling
What are actin filaments?
Semifelxible, polar
What are Intermediate filaments?
Flexible, non-polar
What are Microtubules?
stiff, polar
What is the role of microtubules?
Maintains cell shape
Building block of spindle aparatus
Intracellular transport (railway track)
Motility (cilia, flagella)
What is a microtubule unit?
heterodimer of alpha and beta tubuline
How do microtubules grow?
Bind GTP at beta end (plus end) and hydrolyze to GDP
What are the three phases of Microtubule self assembly?
Lag phase -> slow groth
growth phase (exponential growth)
plateau phase (growth is balanced)
What happens to microtubules if GTP is depleted?
They dissapear rapidly
What does Tau do to microtubules?
Stabilizes the microtubules -> alzheimers Tau- microtubules shrinkage)
How is the centrosome organized?
consists of two centriols with pericentriolar material (PCM)
What are functions of cilia?
signaling function (antenna)
flow of fluid
cellular motility
What is the centrosome duplication cycle?
Centrosomes are assembled (duplicated) once per cell cycle
During mitosis the two centrosomes form the poles of the mitotic spindle , which segregates the chromosomes
Name an MT stabilizing and destabilizing drug
Stabilizing: Taxol: depletes free tubulin subunits
Destabilizing: Nocodazole: inhibits MT assembly
What are actin filaments?
2 filaments twisted around each other
What is a F-actin unit?
globular protein that binds ATP/ADP (ATP hydrolozing activity)
Whats special about actin comapred to MT?
The also polymerize to filaments but they dont spontaneously destabilize (polymerization depends on free actin conc.)
The concentration of G-actin in the cell is 100 x greater than the critical concentration. But 40% of actin in cells
is unpolymerized. Why ?
Regulatory Proteins:binding actin (polymerization only occures at specific places)
Sequestration and Storage: for rapid actin polymerization (motility…)
Cells assemble actin polymers and move faster than they can produce actin. How do they do this?
Actin polymerization generates force and together they multiply that force.
Treadmilling:Assembly at + end and dissassembly at - end -> recycles actin monomers for movement
How Actin Cytoskeleton Generates Force?
Actin polymerization generates force, like a molecular motor. Single actin filament can generate about 5 – 10 pN force. Branched actin filament cooperate and force is 300 nN.
