Updated Scheduling Informa5on Scheduled Final Exam Wednesday December 16 Arjona Hall 8 00 10 00 10 00 12 00 12 00 2 00 2 00 4 00 See Exam Registra5on Link The 2h Final Exam Period will include 2 separate exams 50 ques on Block 4 Exam and a 25 ques on Cumula ve Exam that covers all 4 blocks Review Session 1 Thursday Dec 10th 6 8PM TLS 154 Review Session 2 Last Day of Class Friday Dec 11th 1 25PM Normal Class If you have bunched nal exams or an extenua5ng circumstance and wish to take the Cell Biology Exam 4 Final Exam at one of the two alternate 5mes you must contact the Dean of Students O ce ASAP DOS will then contact Dr DaggeU with o cial no ca on of permission to take the exam at an alternate me Students who do not request permission by December 4th will not be granted permission to reschedule their exams Early Late Final Exam TBA Finishing up Last Week 10 Cell cycle 11 Cell Interactions 12 Cell Movement This Week 13 Specialized Cells 14 Stem Cells 15 Pathogen infected Cells Next Week 16 Cancer Cells 17 Cell Death 18 In class Review Reminder if you need to reschedule your Cell Biology final exam you must contact DOS for approval as soon as possible December 4th deadline approaching Specialized Cells Many di erent cell types rely on specialized cytoskeletal assemblies for their proper func5on Fibroblasts migra on ac n Osteoblasts collagen secre on Neuronal cells growth cone ac n MTs axonal tra cking MTs motors and exocytosis ac n Muscle cells sarcomeres and contrac on ac n myosin Macrophages extravasa on ac n phagocytosis ac n podosome assembly ac n T cells B cells An5gen presen5ng cells immunological synapses ac n Respiratory epithelia Sperm mo le cilia agella MTs motors Sensory cells non mo le cilia primary cilia MTs motors MANY other cells Figure 23 52 Molecular Biology of the Cell Neurons require intracellular transport for the proper distribu5on of neuronal proteins and organelles Nature Reviews Microtubules have a unipolar orienta5on within the axon Kinesins and cytoplasmic dynein mediate vesicle transport within the axon Nature Reviews Vesicle movements within axons I hUp www youtube com watch v SyJgz4P Omo Vesicle movements within axons II hUp www youtube com watch v 09DBrhMylGo Synap5c vesicle tra cking at the NMJ Synap c vesicle exocytosis and endocytosis at the axon terminal is a highlycoordinated and wellstudied process with many debatable details Ac n dynamics play a role Synap c transmission at the neuromuscular junc on NMJ triggers muscle contrac on Termina5on of motor neurons at the neuromuscular junc5on NMJ Skeletal muscle 5ssue is comprised of striated mul5 nucleate cells Muscle contrac on is the best understood example of ac n based movement It represents a model for understanding how motor proteins such as myosin generate forces that are important for various aspects of mo lity The three major classes of muscle are skeletal cardiac and smooth Skeletal and cardiac are called striated because they appear striped under the light microscope Skeletal muscle in par cular has a very regular internal structure that has facilitated our understanding of the mechanism of contrac on These images depict myoblast fusion DNA F ac5n Figure 23 48 Molecular Biology of the Cell Garland Science 2008 D Drubin Muscle cells and sarcomere structure The muscle bers of skeletal muscle myo bers are huge cells that contain mul ple nuclei Myo bers are comprised of mul ple individual contrac le bundles called myo brils Each myo bril consists of a chain of small contrac le units called sarcomeres The sarcomere is composed of thin laments and thick laments Thin laments are composed of ac5n laments and ac n binding proteins The ac n laments are oriented with their barbed ends facing the Z disk Thick laments are composed of hundreds of myosin II motor molecules The coiled coil tail domains of myosin II molecules mediate assembly into the lament Thick laments are bipolar the heads are at opposite ends of the lament and are separated by a bare zone Other proteins help establish and maintain the structure of the sarcomere Leiomodins are the ac n nucleators that are thought to create the ac n laments in muscle D Drubin Sarcomere organiza5on and ABPs The ends of ac n laments are aUached to the Z discs at either end of the sarcomere The end capping protein CapZ and the bundling protein ac nin mediate this interac on The ends of ac n laments are capped by tropomodulin Thus CapZ and tropomodulin stabilize ac n in the sarcomere by preven ng both polymeriza on and depolymeriza on A single molecule of the protein nebulin wraps along the en re length of the thin lament and has been suggested to act like a molecular ruler to control the length of thin laments The huge 2 7MDa brous protein n connects the ends of myosin thick laments to the Z disk and extends along the lament to the M line half the length of the sarcomere Ti n is thought to func on as a spring to keep thick laments centered in the sarcomere when the muscle contracts or is stretched M line D Drubin The sliding lament model of muscle contrac5on Sarcomeres shorten during muscle contrac on The sliding lament model 1954 proposes that sarcomere shortening is caused by myosin laments sliding past the ac n laments with no change in the length of either kind of lament The interac on of myosin heads on thick laments with thin laments can be observed by electron microscopy as crossbridges By hydrolyzing ATP during the cross bridge cycle myosin moves towards the barbed end of ac n laments at the Z disk Because the myosin lament is bipolar it pulls the thin laments and the Z disk towards the center of the sarcomere causing sarcomere shortening D Drubin ATP and Ca 2 drive skeletal muscle contrac5on Muscle contrac on occurs when a signal passes to the muscle from its motor nerve This triggers an ac on poten al in the muscle cell that spreads down the transverse tubules T tubules membrane invagina ons that extend into the cytosol of the myo ber This signal passes to the sarcoplasmic re5culum SR an ER like network of tubules that store Ca 2 Release of Ca 2 from the SR ini ates muscle contrac on Myosin will not bind to ac n in muscle cells unless Ca 2 is present D Drubin ATP and Ca 2 drive skeletal muscle contrac5on Myosin will not bind to ac n in muscle cells unless Ca 2 is present Tropomyosin and troponin prevent myosin binding in the absence of Ca 2 Tropomyosins form a chain along the thin lament In the absence of Ca 2 tropomyosin blocks the movement of