Cytoskeleton

Question 1

What are actin filaments?

Answer 1

Helical polymers of the protein actin called f actin
Monomers are g actin
Diameter of 8nm
Organise into 2d networks, 3d gels.
Concentrated in cortex (under plasma membrane)

Dynamic

Question 2

Microtubules?

Answer 2

2x isoforms –> alpha and beta tubulin - formed in cell and uses dimeric structure to build micro tubules.

Hollow cylinders, 25nm diameter

Centrosome in animals

Growing and shrinking ends

Question 3

What are intermediate filaments?

Answer 3

Eg kerotin
Not found in all kingdoms

Diameter 10nm
Made of intermediate filament proteins
Can for, mesh work called nuclear lamina underneath nuclear membrane

Can extend across cytoplasm giving mechanical strength

Question 4

What is nucleation?

Answer 4

Helical polymer is stabilised by being in contact with multiple other monomers.
Dimers (2 monomers) bind weakly and go back to being monomers
Need 3 or more to be him forming a nucleus

Question 5

How does ATP affect the formation of f-actin?

Answer 5

ATP bound g actin have higher affinity to other monomers, so are more stably integrated into the polymer

However, overtime actin monomers can hydrolyse ATP–> ADP. (-Ve end) and this makes it less stable and f actin begins to fall apart

Question 6

Stages of formation of actin micro filaments?

Answer 6

Lag - time taken for nucleation

Growth phase - when monomers add to exposed ends of growing filaments causing elongation

Equilibrium phase - reached when growth and disassembly balances

Question 7

What does arp 2+3 do?

Answer 7

Nucleation protein

Arp 2+3 complex is activated, and binds to monomer (minus end) and brings g actin together to form nucleating complex

Also aids branching, by binding to existing actin micro filaments…. At 70 degrees

Question 8

What does profilin do?

Answer 8

High affinity for ATP bound g actin.
Can prevent nucleation by binding to all the g actin with ATP, but once initiation happens, quickly nucleatex

Adds g actin to plus end

Question 9

What’s cofilin/ADF?

Answer 9

It induces additional twist in the actin filament which makes it more easy to break

Attracted to ADP bound parts of f action

Promotes subunit loss at minus end or shorter actin fragments

Question 10

What are gamma tubulins?

Answer 10

It forms complex for initiation of nucleation for micro tubulins

Gamma tubulin ring complex

Part of centrosome in animal and yeast cells

Joins with association proteins to form structure

Question 11

Centrosomes?

Answer 11

Form in animal and yeast cells

Diff in plant cells - small dispersed nucleus

Question 12

What is dynamic instability in micro tubule?

Answer 12

Micro tubules depolymerise 100 times faster from an end containing GDP than GYP.

GTP cal favours growth, and if it’s lost the tubulin falls apart

Question 13

What does katanin do?

Answer 13

Binds to ATP, pray itself into micro tubules structure and breaks micro tubules into 2

By doing so, it can promote growth in a certain direction

Eg. Plant growth, micro tubules start growing longitudinally once exposed to light. Thanks to katanin

Question 14

What is cytoskeleton made of?

Answer 14

Actin and micro tubules and intermediate filaments

Question 15

What is kinesin?

Answer 15

A motor protein.
Motor subunits - KHC - heavy chains - interact with micro tubules - n terminal

Interaction with cargo - c terminal - two light chains KLC

Question 16

How does Kinesin work?

Answer 16

ATP hydrolysis changes the conformation of the motor domains, so that there is an apparent shift in location

Might step over each other, or trailing… Dunno

Move towards PLUS END

Question 17

What are kinesin light chains?

Answer 17

They are connected to the ends of the ‘necks’ of the kinesin………………..
They can interact directly or indirectly with cargo

Light chain has TPR and variable c terminal Domain. This domain can specifically interact with proteins on vesicles

Question 18

How do we look at kinesin behaviour in vitro?

Answer 18

Add kinesin Fluro protein, and ATP.
Working as cargo

USE gold cargo for better res to see steps

Question 19

What do kinesins do when there’s a obstacle?

Answer 19

Tries to side step

Some fall off

Question 20

What is dye in

Answer 20

Motor protein
Moves to minus end
Uses ATP to fuel

12 subunits
Donut shaped head - where ATPase happens

Stalk binds to microtubule

Question 21

What is a dyenin receptor

Answer 21

Dynactin

Protein complex that binds to end of dyenin which enhances interact film between dyenin and cargo

Question 22

What happens when both kinesin and dyenin bound to a cargo?

Answer 22

Usually kinesin is stronger (5 fold)

But when cAMP level is low, dyenin will win

(Cyclic amp)

Question 23

What is myosin?

Answer 23

Actin based motor protein

Moves really fast 7micrometers per sec

Light chains bound to motor proteins

Work by hydrolysing ATP

P

Question 24

How does myosin move?

Answer 24

Takes long steps, head domain binds actin, uses ATP hydrolysis to walk along filament

Walks to plus end

Tail mediates interaction with cargo

Question 25

How does myosin work in muscles?

Answer 25

Thick filament - myosin
Thin - actin
Head domains stick out from sides of filaments ready to walk along adjacent actin based filaments when muscle is contracted

Myosin head hydrolysis atp, then binds to actin, then then bind ATP, detach from actin

Question 26

How is cell migration fuelled by actin polymerisation ?

Answer 26

Protein called integrin links the cell to the surface(substrate) and let’s go at the back

Actin polymerisation, and through myosin, it pushes the actin forward

Question 27

What is the cellulose synthase complex in plant cells?

Answer 27

Cellulose micro fibrils - tensile strength equal to steel

How you’ve laid these down determines how the plant grows… Can only expand in those directions

Cellulose is synthesised by a large protein complex that moves along micro tubules (joined by CS1)

Catalytic activity of this complex moves along micro tubules

Question 28

Are dyenin in plant cells?

Answer 28

Nah