Intro To Cytoskeleton And Microtubules Flashcards
What is the cytoskeleton made of
Microtubule
Microfilaments (actin filaments)
Intermediate filaments
What are the general functions of the cytoskeleton and what helps do them
Structural support (shape, actin filaments, intermediate filaments, microtubules)
Transport of materials/ organelles in the cell (motor protiens)
Contraction and motility (forming motor forces)
Spatial organization
Cell division
Are microtubules polar or non polar
Polar
What a description of microtubules
Stiff hollow inextensible tube
Provided mechanical support since their stuff enough to resist compression of bending forces
Help determine shape of the cell
Maintain the intracellular location of the organelles
What are each type of cytoskeleton filaments made up of
Why is this helpful
Made of protein subunits that are held together by weak non covalent bonds
This help for assembling and disassembling the protien easily
What are microtubules made of
They’re hollow unbranched structures that are made of tubulin
Each tubule is made up of 13 protofilaments (made of tubulin)that are aligned side by side to form the tube
What is the role of microtubules
Cell support and movement of materials (though motor protiens)
Extend across either the length or the breadth of the cell (depending on the needs of the cell)
What are protofilaments made of
What does this do
They are made from dimers of one alpha tubulin and one beta tubulin
This causes polarity due to he asymmetry of the protofilaments, there is a alpha tubulin end and a beta tubulin end
Which end of the protofilaments is postive
Which is negative
Beta is positive
Alpha is negative
Not actually -/+ charge, just diff properties, beta is GDP alpha is GTP
What is the centrosome
A microtubule organizing centre that begins the microtubule formation (microtubules stem from it)
It remains at the centre of the cells microtubular network
What is the centrosome made of
Two centrioles that are surrounded by pericentriolar material (PCM)
The centrioles are like cylinders made of microtubules
The PCM is a loosely organized fibrous lattice
What happens when centrosome replicate
The centrioles make the PCM form a new centrosome
What do centrosome dictate
What DONT they dictate
The number of microtubules
The polarity of the microtubules
The number of protofilaments that make up the microtubule
The time and location of the assembly of
Microtubules
They DONT dictate the stability of rate of formation of the microtubules
When now microtubules are formed what do the actually make contact with
Not the centrioles, they are initiated in the PCM
What is the PCM made of
Gamma TURC (tubulin ring complex) which is made of
GAMMA tubulin and non tubulin protiens in a ring
How are new microtubules added to the PCM
The gamma tubiln protiens are on top of the non tubulin protiens. This forms the gamma TURC.
The alpha beta tubulin dimers are added onto this gamma TURC (on top of the gamma tubulin)
Only the alpha tubulin can first be added into the gamma tubulin
How do microtubules act in diff situations
For mitotic spindles they’re sensitive to disassembly
For neurons cillia and flagella they are very stable
What determines the stability of the microtubules
Determined by microtubule interacting proteins (MAPS)
And +TIPS which bind at the + end of the growing microtubule (beta end)
Temperature: if cold the microtubules disassemble
what does MAPS do
What are they controlled by
It increases the stability of the microtubules and promotes their assembly by linking the tubulin dimers together, some can also decrease stability
They’re activity is controlled by the presence of phosphate groups
Ex high amount of phosphorylated MAPS (called tau) leads to Alzheimer’s
What type of protien is beta tubulin
What does this means
It’s a g protien
Means that after it’s added to the microtubule it hydrolysis GTP to GDP, this affects the structure of the microtubule
This GTP is required for the microtubule to assemble
What type of protien is alpha tubulin
NOT a g protien, so it’s stays with GTP which isn’t hydrolyzed to gdp
What is step one of how a microtubule is elongated
The tip originally had tubulin GTP dimers that are in an open sheet (not cylinder)
These are beta tubulin
What is step 2 of how a microtubule is elongated
The GTP hydrolyses to GDP and the open sheet close to form the tube
What is step 3 of how a microtubule is elongated
The gdp tubulin has a different conformation that makes it want to curve outward instead of in to form the tube
This introduced mechanical strain, so the MAPS come in and stabilize the microtubule
What is step 4 of how a microtubule is elongated
If MAPS are absent and aren’t stabilizing, the protofilaments curl outward and undergo CATASTROPHIC SHRINKAGE
What do + TIPS do
They bind the the + beta end of the microtubule and regulate the rate of tubule growth or shrinkage
They mediate the attachment of microtubules to subcellular structures (like the kinetochore of the chromosome)
What is the benefit of microtubule polymerization and disassembly
The polymerization can help push material and elongate the tubule
The disassembly can help pull material and shorten the tubule
Is the cytoskeleton on the outside of the cell
No
