L312/Spring 2006 Lecture 16 Drummond March 6

1. L312/Spring 2006 Lecture 16 Drummond March 6 For today: Focus on Ch. 17 Actin and myosin, movement 595-607 Contribution of ATP to kinesin/myosin motor function What drives the process? Revisit today Thursday: Exam II! Do we need another review session today/tonight? Today: Finish consideration of actin filaments last time: size, composition, contribution to the cell structure and movement today, focus on: lamellipodia, filopodia, ARPs (actin related proteins) integrins capping proteins, depolymerizing proteins, Questions: How is the signal to move transmitted to the inside of the cell? How can actin be used to move the cell? Why are integrins essential for cell migration? What is the role of myosin in movement? What is the structure of muscle fibers and how does structure relate to function? You are responsible for the role of calcium in muscle cell contraction--how does a rise in calcium mediate muscle contraction?

2. Re-thinking the role of proteins in cellular structure and function Intermediate filaments, Microtubules and actin as reversible, modular, remodelable fibers for structure, strength, transport and organization

3. Actin filaments: Where: remember that actin filaments comprise the cell cortex (plus many other roles) why NOT microtubules or intermediate filaments?

4. Contexts for finding actin filament function (how can a 7 nm fiber carry out all these roles?) Lamellipodia (sheets) Filopodia (fingers) Contractile bundles Villi support Contractile rings

5. Actin filaments contain a single, polar protein monomer Thin, flexible, 30X volume Vs microtubules ATP/actin adds here

6. How does actin polymerization move the leading edge of the cell? ARPs are essential for lamellipodia formation

7. Different extracellular signals trigger different actin responses What is the experiment here? Think about regulation in a broader context-- What do extracellular signals do to the cortex? How are all the responses integrated?

8. Anchoring points to a glass slide (human fibroblast) Reflection/interference fluorescent antibody to actin

9. The actin superhighway Key questions: how does myosin-1 resemble kinesin? How does actin resemble microtubules? What is the key rule about direction of movement? Why vesicles? (now granules with mRNA) Move cargo Move cell

10. Add ATP Release Step/reattach Dissociate ADP Football game analogy

11. How does this compare with the role for ATP in the kinesin ‘walk’

12. How are myosin-II distinguished from myosin-I family proteins? What holds the two monomers together?

13. How can the relative movement of actin and myosin bring about cell contraction? What drives this process?

14. How do actin/myosin interactions support muscle contraction? What are muscle fibers? How big are they? Why are they multinucleate?

15. What is the relative layout of actin and myosin here? 1 ATP hydrolyzed/cycle per myosin head 5 nm movement to + end Each myosin filament has 300 heads Cycle (attach/detach) at a rate of 5/second 15 µm / second movement

16. How is movement of actin related to contraction?