Microtubules Flashcards
Main function of Microtubules
The organizer of the Cell
-Transport: Create tracks that vesicles, organelles, and other cellular components move along
-anchor organelles
-form mitotic spindles for chromosome segregation
-form Cilia and flagella structures.
Microtubule Structure:
Built from dimer subunits of alpha and beta tubulin proteins
-tubulin stacks together by non-covalent bonding to form protofilaments
Protofilaments
tube structure composed of 13 protofilamets lined up side by side
do microtubules have polarity?
Yes.
Beta tubulin is positive
Alpha tubulin is negative
Where do microtubules originate?
Centrosome
-this is where the tubulin units polymerize from nucleation sites
Nucleation Sites
Starting point of microtubulin growth
- Alpha/Beta tubulin dimers are added to the positive end of the y tubulin
**mins end is anchored
Dynamic Instability
Microtubules Grow and Shrink
How does the Growth of Microtubules occur?
Controlled by the rate of GTP Hydrolysis
- each free tubulin dimer is bound to GTP and is added to the growing microtubule
-GTP and eventually hydrolyzed to GDP
-GTP bound tubulin is binded tightly compared to GDP
When is the Polymerization of Microtubules rapid?
dimers are added to the plus end of beta-tubulin at a faster rate resulting in a GTP CAP where the microtubule continues to grow
What is microtubule growth controlled by?
The Rate of GTP hydrolysis
Microtubule Stabilizing Protein
MAPS: Tau Proteins bind to hetero-dimers for stabilization
-binds to GDP
Review Slides 8-14 Part 1
8-14
Microtubule Function
Guide Transport
-have transport proteins
Transport Proteins contain…
2 Globular Heads
-that bind to the microtubule
bind to ATP and Hydrolyze if to provide energy for conformational changes which allows the motor proteins to move along the microtubule
A Tail
-binds to either a vesicle of an organelle, determines cargo for motor protein
Kinesin
Motor Protein that moves away from the centrosome and towards the plasma membrane
-moves to the positive end
Dynein
Motor Protein that moves toward the nucleus
-move toward the negative end
the Tail of Motor Proteins
transports different cargos, tail region has specificity for a variety of cargo.
Microtubules and Motor Proteins Function:
-Microtubule Transport
-Position Organelles
-Help form Cilia and Flagella (no motor protein)
Flagella
propel a cell through fluid using repetitive wave-like motion
-propel sperm and protozoa
Cilia and Flagella Structure
9+2 Arrangement
-9 doublet microtubules in a ring around a pair of 2 single microtubules in the center.
What causes the flagellum to bend?
Dynein Motor Protein
-generates bending motion
-Doublets are tied to each other by flexible protein links that allow bending NOT sliding
