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YEAR I TUTORIAL: MUSCULOSKELETAL SYSTEM

Cells require movement.... WITHIN cells Vesicle movement, chromosome movement in mitosisCELL movementsPhagocytosis Bacterial motility. MOVEMENT USES PROTEIN ASSEMBLIES.... Chemical energy? mechanical workThis energy can come from:- ATP hydrolysis- ion gradient?Motors' may be

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YEAR I TUTORIAL: MUSCULOSKELETAL SYSTEM

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    1. YEAR I TUTORIAL: MUSCULOSKELETAL SYSTEM Reenam Khan- 2nd year medic reenam.khan06@imperial.ac.uk

    2. Cells require movement... WITHIN cells Vesicle movement, chromosome movement in mitosis CELL movements Phagocytosis Bacterial motility

    3. MOVEMENT USES PROTEIN ASSEMBLIES... Chemical energy? mechanical work This energy can come from: - ATP hydrolysis - ion gradient ‘Motors’ may be: Linear Rotary Oscillatory

    4. LINEAR MOTORS: Require protein rails i.e. Something to move along. Example = KINESIN (protein rail= microtubules)

    5. OTHER LINEAR MOTORS... Myosin (requires actin filaments) Dynein (uses microtubules) NCD (uses microtubules) Helicases/ topoisomerases (use DNA/RNA) Other linear motors rely on filament polymerisation: eg actin polymerisation in listeria to move into infected cells or microtubule polymerisation

    6. Listeria using actin polymerisation:

    7. OSCILLATORY MOTORS: In cilia e.g. sperm tails, respiratory tract Require cross-linked microtubule bundles (axonemes) Powered by dynein (motor proteins)

    8. Cilia in action:

    9. ROTARY MOTORS Require stators- something that doesn’t rotate to hold it in position!

    10. ROTARY MOTORS Example 2= flagellar motor

    11. myosin Many different types Myosin V ? vesicle transport Myosin II ? skeletal and cardiac muscle contraction

    12. Lots of myosin molecules (294)? thick filaments

    13. Actin filaments: Polymer of G-actin (43 kDa globular protein) In most cells, found at the periphery, underlying the cell surface ‘thin filaments’ in muscle Also in microvilli Also involved in cell shape changes

    14. Skeletal muscle structure:

    15. SARCOMERE STRUCTURE

    16. Calcium release mechanism

    17. ACTIVATION OF SKELETAL MUSCLE CONTRACTION

    18. Cross-bridge cycle:

    19. Characteristics: Energy source= ATP. If absent? rigor mortis One-way filament sliding Small step size- 1 cycle= 1% of sarcomere’s length

    20. Isometric contractions- no length change...

    21. Varying the force produced: Recruitment: Motor unit= motoneurone all the fibres it innervates. Size varies.

    22. 2) Stimulation frequency

    23. 3) Filament overlap

    24. 4) Velocity and direction of movement

    25. WHERE DOES THE ATP COME FROM? 1) Some is stored directly 2) Creatine kinase: 3) Glycolysis- using glycogen/glucose. Lactic acid made 4) Oxidation- using glucose/glycogen/fatty acids

    26. Different energy sources for different activities:

    27. CARDIAC MUSCLE

    29. Cardiac muscle: two ca2+ sources

    30. Smooth Muscle

    32. QUESTION TIME! Actin is found in thick filaments Smooth muscle has filaments Regarding the cross-bridge cycle: 3) Tropomyosin binds Ca2+ 4) ATP binding to myosin causes ‘power stroke’ Regarding motors: 5) Linear motors require protein rails 6) Rotary motors require axonemes 7) An example of an oscillatory motor is kinesin

    33. QUESTION TIME! 8) The dihyrdropyridine receptor is a voltage sensor 9) The ‘light bands’ of sarcomeres are caused by thin filaments 10) The longer the length of a sarcomere, there greater the amount of force produced in muscle contraction.

    34. Thank you

    35. REMINDERS: Membership Next tutorial - send any feedback for the tutorial to nj104@ic.ac.uk or bh04@ic.ac.uk The lecture slides will go online, check the website: http://www.union.ic.ac.uk/medic/muslim/ Any help from us? Please email rk206@ic.ac.uk

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