MCB Lecture 35 Cytoskeleton II Flashcards
In muscle contraction, hydrolysis of ATP on the myosin head prompts what?
The head cocks and binds to the actin filament
Describe how myosin causes actin filaments to move
- ATP binds, and the head dissociates from actin
- ATP is hydrolysed, head cocks and it binds to actin
- Dissociation of the phosphate triggers the power stroke
- ADP dissociates during the power stroke
What triggers the power stroke?
The dissociation of the phosphate
What does ATP binding to myosin trigger?
The dissociation of the myosin head from actin
Describe the three stages in cell locomotion
- Protrusion
- Adhesion
- Traction
Describe the attachment phase of cell locomotion
New focal contacts are made at the mobile side of the cell
Old focal adhesions at the other side are removed
Describe the traction phase of cell locomotion
Focal adhesions produce Cell traction forces
Myosin rearranges the actin, producing stress and contractile forces
How are cells guided when they move?
They follow chemical gradients or molecules
How do bacteria cells know where to go when they move?
- Chemoattractants bind to receptors on the surface of bacteria
- One of two pathways is activated:
2a. Rac: actin polymerisation
2b. Rho: myosin activity
Describe the formation of Microtubules
Tubulin dimers form
Dimers arrange head to tail to form a protofilament
13 Protofilaments line up side on to form a tube
9 double tubes arranged in a circle, with 2 in the middle form a microtubule
What is the structure of a protofilament of a microtubule?
It is a strand of dimers connected head to tail
Describe the polarity of a microtubule protofilament
+/beta end
-/alpha end
What are some functions of microtubules? (3)
Form tracts around the cell
Cilia and flagella
Mechanical work
What is the function of the GTP-cap?
What happens if it lost?
A GTP-cap binds to the beta end and stimulates polymerisation
Without a GTP-cap, catastrophes are much more common and the filament depolymerises
Describe polymerisation of microtubule protofilaments
Dimers added to the protofilament on the beta end
What is the rate limiting step in microtubule formation?
Nucleation, formation of an oligomer that has enough H bonds to be stable and for polymerisation to then occur
Which complex speeds up nucleation of microtubules?
Gamma-Tubulin ring complex
Which organelle produces microtubules?
Describe its structure
Centrosome
It is a sphere with two centrioles
The sphere is perforated with gamma-Tubulin Ring Complexes that increase rate of polymerisation
What is the function of proteins that bind to micro filaments?
They increase stability, so that the microfilament can form a tract around the cell
Describe the function of MAP
MAP binds to the GTP Cap on the plus and reduces the frequency of catastrophes by stabilising the filament
We thus get a longer, more stable filament
… microtubule forms tracks around the cell
Stabilised
Which motor proteins move materials around on the microtubule cytoskeleton?
Kinesin and Dynein
Differentiate between Kinesin and Dynein
Kinesin moves stuff anterograde: toward the plus end
Dynein: moves stuff retrograde: towards the minus end
Describe how motor proteins generate force
ATP hydrolysis couples with conformational changes
How do Kinesin and Dynein interact with the microtubule?
In a similar way that myosin interacts with actin filaments
How do Kinesin and Dynein associate with vesicles?
Through many proteins
Describe the dynamic instability of microtubules, and how catastrophes occur
When a GTP-cap is lost, the microfilament rapidly depolymerises.
During migration, actin polymerisation preferentially occurs at which end of the cell?
The extending end
What is important about the dimer that forms microtubule filaments?
It is a heterodimer: alpha and beta subunit
What is the structure of a microtubule?
13 protofilaments
What is the structure of microtubules in cilia and flagella?
9 + 2
Wat is meant by the dynamic instability of microtubules?
They undergo phases of rapid polymerisation as well as rapid depolymerisation
What can lead to decreased stability of the GTP cap?
Hydrolysis of the GTP to GDP
What are the three types of Tubulin monomers?
Alpha, beta, gamma
How do we control where we want to synthesis microtubule?
The controsome can be moved around the cell
How can microtubules be destabilised?
Binding of certain proteins to the GTP Cap
What is the role of cytoskeleton in the bio secretory pathway?
Vesicles travel along microtubule
