1. The Cell Cytoskeleton1 Chapter 17 Questions in this chapter you should be able to answer: Chapter 17: 1 - 11, 13 - 23 Watch this animation http://multimedia.mcb.harvard.edu/ anim_innerlife.html The Inner Life of Cells

2. The Cell Cytoskeleton2 What are the 3 primary types of cytoskeletal proteins? Intermediate filaments -- resist mechanical stress Microtubules -- cytoplasmic transport -- axoneme movement -- chromosome movement Actin filaments -- membrane contraction -- muscle cells -- cytokinesis -- cell movements

3. The Cell Cytoskeleton3 What is the structure of intermediate filaments Cable-like arrangement Extended molecular interactions Anchoring to desmosomes Intermediate Filaments Intermediate Filaments

4. The Cell Cytoskeleton4 Distribution and functions of IFs? Cytoplasmic -- keratins – skin integrity  -- in neurons -- in muscle, connective tidssue Nuclear -- lamins -- progeria connection??

5. The Cell Cytoskeleton5 What is the fundamental structure of microtubules? Alpha and beta tubulin subunits 13 member ring Why do MTs have polarity? ‘MT Organizing Center’ Why are MTs said to display ‘Dynamic Instability’? Dynamic Instability

6. The Cell Cytoskeleton6 What is the mechanism of MT growth and retraction? Binding, hydrolysis and release of GTP ‘Capping’ at cell membrane Question 17-3, p 583 How would a change in [tubulin] affect MT dynamics?..if only GDP were present? … or a nonhydrolizable GTP analog? MT with EB1 cap

7. The Cell Cytoskeleton7 How do MTs facilitate cytoplasmic transport? Motor proteins kInesin & dynein Kinesin walking Organelle movement

8. The Cell Cytoskeleton8 What is the structure and movement of an axoneme? Cilia & flagella “9 + 2 Structure” Lining Cell video

9. The Cell Cytoskeleton9 Axoneme mutations and Immotile Cilia Syndrome Diagnosis Symptoms; respiratory infection; situs inversus, flagella and embryonic development - IDA - ODA - IDA Morillas HN, Zariwala M, Knowles MR. 2007. Genetic Causes of Bronchiectasis: Primary Ciliary Dyskinesia. Respiration 2007;74:252-263

10. The Cell Cytoskeleton10 What is the distribution and structure of actin filaments? treadmilling

11. The Cell Cytoskeleton11 How are actin filaments organized in the cytoplasm? The cell cortex Actin binding proteins

12. The Cell Cytoskeleton12 How does actin mediate cell movements? Cell crawling What are Lamellipodia and Filopodia? Membrane ruffling Listeria movement Listeria movement

13. The Cell Cytoskeleton13 Actin, myosin and muscle contraction Some basic anatomy... Muscle are bundles of muscle cells Muscle cells contain myofibrils Sarcomere is contractile unit of myofibril

14. The Cell Cytoskeleton14 How are actin and myosin arranged within a sarcomere? Structure of a myosin-II thick filament Myosin motor proteins I & II

15. The Cell Cytoskeleton15 How does myosin interact with actin filament? What happens to the sarcomere during contraction?

16. The Cell Cytoskeleton16 Myosin is attached ATP binds -- Myosin head detaches ATP is hydrolyzed -- Myosin Head cocks -- loosely binds to actin Pi is released -- which triggers …. Powerstroke -- during which… ADP is released Myosin remains attached How does the sliding filament model explain sarcomere contraction? myosin

17. The Cell Cytoskeleton17 How is muscle contraction triggered? Motor neuron & action potential Sarcoplasmic reticulum T-tubules Ca ++ release

18. The Cell Cytoskeleton18 How does Ca++ trigger the muscle contraction? The tropomyosin / troponin complex Sarcomere

19. The Cell Cytoskeleton19 Question In order to keep cytosolic Ca ++ levels low, muscle cells possess an ATP driven Ca ++ pump in the sarcoplasmic reticulum and a Ca ++ /Na + ATPase in the cell membrane. The cells also possess the Na + /K + ATPase in the cell membrane. The Na + /K + ATPase is partially inhibited by drugs such as ouabain and digitalis, whereas the Ca ++ /Na + ATPase is inhibited by binding to a protein called phospholamban. A. Draw a diagram showing the expected arrangement and orientation in the membranes of these membrane proteins. B. Would treating a patient with either of these drugs weaken or strengthen muscle contraction (they are usually given to cardiac patients)? Explain. C. The regulatory protein “protein kinase C” (PKC) regulates activity of the Ca ++ ATPase. PKC can phosphorylate (covalently add a PO 4 ) to the Ca ++ ATPase, which increases its affinity for Ca ++. What would be the expected effect of Ca ++ ATPase phosphorylation on the strength of muscle contraction?