Intro To Cytoskeleton And Microtubules

Question 1

What is the cytoskeleton made of

Answer 1

Microtubule

Microfilaments (actin filaments)

Intermediate filaments

Question 2

What are the general functions of the cytoskeleton and what helps do them

Answer 2

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

Question 3

Are microtubules polar or non polar

Answer 3

Polar

Question 4

What a description of microtubules

Answer 4

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

Question 5

What are each type of cytoskeleton filaments made up of

Why is this helpful

Answer 5

Made of protein subunits that are held together by weak non covalent bonds

This help for assembling and disassembling the protien easily

Question 6

What are microtubules made of

Answer 6

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

Question 7

What is the role of microtubules

Answer 7

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)

Question 8

What are protofilaments made of

What does this do

Answer 8

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

Question 9

Which end of the protofilaments is postive

Which is negative

Answer 9

Beta is positive

Alpha is negative

Not actually -/+ charge, just diff properties, beta is GDP alpha is GTP

Question 10

What is the centrosome

Answer 10

A microtubule organizing centre that begins the microtubule formation (microtubules stem from it)

It remains at the centre of the cells microtubular network

Question 11

What is the centrosome made of

Answer 11

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

Question 12

What happens when centrosome replicate

Answer 12

The centrioles make the PCM form a new centrosome

Question 13

What do centrosome dictate

What DONT they dictate

Answer 13

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

Question 14

When now microtubules are formed what do the actually make contact with

Answer 14

Not the centrioles, they are initiated in the PCM

Question 15

What is the PCM made of

Answer 15

Gamma TURC (tubulin ring complex) which is made of

GAMMA tubulin and non tubulin protiens in a ring

Question 16

How are new microtubules added to the PCM

Answer 16

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

Question 17

How do microtubules act in diff situations

Answer 17

For mitotic spindles they’re sensitive to disassembly

For neurons cillia and flagella they are very stable

Question 18

What determines the stability of the microtubules

Answer 18

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

Question 19

what does MAPS do

What are they controlled by

Answer 19

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

Question 20

What type of protien is beta tubulin

What does this means

Answer 20

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

Question 21

What type of protien is alpha tubulin

Answer 21

NOT a g protien, so it’s stays with GTP which isn’t hydrolyzed to gdp

Question 22

What is step one of how a microtubule is elongated

Answer 22

The tip originally had tubulin GTP dimers that are in an open sheet (not cylinder)

These are beta tubulin

Question 23

What is step 2 of how a microtubule is elongated

Answer 23

The GTP hydrolyses to GDP and the open sheet close to form the tube

Question 24

What is step 3 of how a microtubule is elongated

Answer 24

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

Question 25

What is step 4 of how a microtubule is elongated

Answer 25

If MAPS are absent and aren’t stabilizing, the protofilaments curl outward and undergo CATASTROPHIC SHRINKAGE

Question 26

What do + TIPS do

Answer 26

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)

Question 27

What is the benefit of microtubule polymerization and disassembly

Answer 27

The polymerization can help push material and elongate the tubule

The disassembly can help pull material and shorten the tubule

Question 28

Is the cytoskeleton on the outside of the cell

Answer 28

No