lecture 10 - cytoskeleton Flashcards
What are motor proteins?
Use ATP hydrolysis as energy to move along cytoskeleton. Motor proteins that move along actin filaments are called myosins
Myosin can bind and hydrolyze ATP
This provides the energy for their movement along actin filament from the minus end towards the plus end
How does the myosin move the actin filaments?
Attached: head lacks ATP and is locked onto the actin filaments
Released: When ATP binds to myosin a conformational change this reduces affinity for the myosin filament
cocked: ATP to ADP, large conformational change causes head to be displaced along the filament
Force generating: new weak binding to actin filament, causes release of inorganic phosphate and tight binding to actin. Releases power stroke in which the head retains its original conformation and then releases the ADP
How can organelles move through the cell?
movement of mesons attached to cellular organelles can move organelles along actin filaments
How do muscle contracts?
The myosin header move towards the plus ends of the actin filaments pulling the z-discs together
What are microtubules made up of?
long hollow cylinders made up of tubular monomers
How big are microtubules?
25nm in diameter
How are microtubules different from actin / intermediate filaments?
more rigid and straight
Where do microtubules grow from?
Grow from a microtubule organising centre
What are microtubules made up of?
Tubulin made up of a dimer of a and b tubulin
Subunits stack together to form a hollow cylindical microtubule
How many subunits can be observed when looking down a microtubulin ?
13 protofilaments
How are microtubules maintained?
balance between assembly and disassembly
A cell contains a mixture of microtubules and free tubulin
Microtubules are unstable allowing them to undergo rapid remodelling
What is the centrosome?
Located in the cytoplasm just outside the nucleus
Microtubules grow out from the centrosome
What are centrioles?
ylindrical organelle composed mainly of a protein called tubulin
What controls the growth of microtubules?
GTP hydrolysis
How is a GTP cap formed an what does it do?
If new subunits (which have GTP bound to beta tubulin) are added quicker than beta tubulins hydrolyses GTP, a GTP cap will form. When a GTP cap is present the microtubule end is stable and can continue to grow.
How does a microtubule shrink?
If GTP is hydrolysed faster than new subunits are added the GTP cap is lost.
How are microtubules stabilised?
Interacting proteins
What is a summary of the overall function of microtubules?
Cellular organisation, movement of organelles, cell polarity
Cell division, mitosis, meiosis
Cilia and flagella
What are two types of Motor proteins?
Kinesins and Dynesins
What end of the microtubules do dyneins move?
Towards the minus end of the micrtubles
What end of the microtubules do kinesins move?
Generally move towards the minus end of the microtubules
What are two things that Kinesins and Dyneins have in common?
Both have two ATP binding heads and a tail
Both have ATPase activity
What are Kinesins and Dyneins?
motor proteins
What drives the movements of motor proteins along microtubules?
- ATP hydrolysis
provides conformation changes in the head that allows it to move along the microtubule
Where is the Golgi situated in the cell and how does it get there?
It is situated on one side of the nucleus close to the centrosomes.
Dyneins pull it here
Where is the ER directed to?
The opposite side of the cell to the Golgi
What is the effect of Nocodazole?
Nocodazole is a drug that interferes with polymerisation of microtubules
- When cells are treated with nocodazole the microtubules disassemble, the Golgi fragments and is found more ‘spread out’ in cells.
Where is the centrosome located?
just outside the nucleus
what happens to the centrosome during mitosis?
Just before mitosis the centrosome duplicates
- The two centrosomes move apart
- microtubules grow out from each centrosome with their plus ends growing towards the equatorial plate forming spindle fibres
what are the two drugs that interfere with microtubule assembly?
- Colchicine and taxol
What is the mechanism of Colchicine?
Binds free tubular and prevents polymerisation into microtubules
What is the mechanism of Taxol?
tightly binds microtubules and prevents them from losing subunits
Where do cilia and flagella grow from?
Basal bodies
How are cilia and flagella moved?
contain stable microtubules that are moved by dynein
What is the primary function of cilia?
Cilia extend from the surface of many kinds of eukaryotic cell
Primary function of cilia is to move fluid over a cell or a cell through a fluid
how are cilia and flagella microtubules arranged?
( 9 + 2)
What is the function of the next links ins flagellum and cilia?
- stabilises the microtubules
- causes the structure to bend rather than slide
