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BGYB30 Midterm 2004 • Total number of Marks available= 56 • I will record all of the grades out of 54 total marks. • Small adjustment of +0.5 for different markers • Average mark = 36.4 • Class average after adjustments = 36.4 / 54 = 67.4% BGYB30 Midterm 2004 • Short Answers • Available for pickup next week during TA office hours (Mon 10-12, Wed 12-1) • If you want your test remarked – Compare your grade to posted marking scheme – Tests will be entirely remarked /56 – Your test must NOT leave the office – All requests submitted by 1pm Nov 18 ?? Taste Smell Taste • Contact • 4 basic tastes – Salt, bitter, sweet, sour – Complex mixing for taste perception • All modify synaptic transmission between taste receptor and a sensory neuron • Individual receptor cells respond best to one type of taste and less well to others Smell • Long distance • Many receptors – 1000s mouse – 100-200 human • All receptors are G-protein coupled receptors • Depolarize olfactory cells, leading to APs • Each receptor cell has only one or two types of receptor molecules Complex stimuli Sugars Bitter Ionic stimuli Salt (Na+) Sour (H+) Taste Receptor Second messenger depolarization Na+ Intracellular Ca++ Ca++ Sensory neuron Olfaction Press Release: The 2004 Nobel Prize in Physiology or Medicine 4 October 2004 The Nobel Assembly at Karolinska Institutet has today decided to award The Nobel Prize in Physiology or Medicine for 2004 jointly to Richard Axel and Linda B. Buck for their discoveries of "odorant receptors and the organization of the olfactory system" Na+ Odourant molecule receptor G-protein ATP cAMP glomerulus Olfactory receptor cells with different receptor molecules Taste & Smell • Summary – Both are receive and process external chemical stimuli – Taste receptors modify synaptic transmission – Olfactory receptors generate APs – Many types of olfactory receptors, only a few types of taste receptors Muscle Next Class: BGYB30 Pose-Off Winner 2002 Winner 2003 Muscle Striated Skeletal •movement Cardiac •heart Smooth Blood vessels lungs intestine •Mechanisms of muscle contraction essentially the same •Differences in how muscle cells are organized and how contractions initiated Skeletal muscle Tendon Muscle Bone Muscle Fibers nucleus Myofibril Myofibril Sarcomere (2-3 m) Z M Z H zone A band I band Z Banding patterns due to overlapping protein filaments A I H Z disk Actin filament Myosin filament ‘cross bridges’ Actin filament • When muscle contracts the sarcomere length is reduced REST CONTRACTION STRETCH • Length of filaments doesn’t change • but the degree of overlap does sliding filament hypothesis The degree of overlap is important for generating tension Specifically the number of cross-bridges Relative tension Length – Tension relationship for single sarcomere Stimulator 1.0 0.5 1.25 Control muscle length Measure tension 1.65 2 2.25 Sarcomere length (m) 3.65 1 3 4 Relative tension 2 1.0 3 2 4 0.5 1 5 5 1.25 1.65 2 2.25 Sarcomere length (m) 3.65 • At maximum stretch no overlap • At peak tension optimal overlap • As sarcomere shortens filaments interfere Summary • Muscles made of myofibrils • Myofibrils have sarcomeres Functional unit of muscle contraction • Thick and thin filaments give a banding pattern (myosin and actin) • With contraction sarcomere length changes • Maximum tension produced with optimal overlap of filaments Next Class BGYB30 Pose-Off Winner 2002 Winner 2003 Myosin Tail • assembles into filaments Head • binds Actin • ATPase S2 Link Myosin Light Chains protein filaments of the sarcomere Actin filament Myosin filament ‘cross bridges’ Actin filament Myosin filament Myosin self-assembles into filaments ~150 cross-bridges at each end of the myosin filament Actin filaments • F-Actin (flimanetous) assembles from G-actin (globular) • Actin has myosin binding sites Myofilament chemistry Actin + myosin Actomyosin complex ATP Actin + myosin Actomyosin complex Very slow! Myosin-ATP Myosin-ADP-Pi Myosin +ADP +Pi Releases energy Myosin-ADP-Pi + Actin Actomyosin + ADP + Pi Very fast! Actin rate of ATP hydrolysis by myosin Actin-Myosin Cycle Myosin-ADP-Pi binds Actin weakly Pi Myosin-ADP binds Actin strongly Myosin-ADP Head rotates ADP is released and ATP binds Myosin Myosin-ATP released from Actin Myosin hydrolyzes ATPADP+Pi Myosin-ATP • Transition between weakly bound and strongly bound complex generates tension Actin filament Binding sites Strong binding Weak binding Myosin head group S2 link Stretching of the link generates tension Myosin filament Why do thin filaments move? Net force Net force Equal and opposite force on thick filament What if we don’t have this? X ATP Actin + myosin Actomyosin complex Rigor mortis Role of calcium • Intracellular Calcium is required for muscle contraction • Used ‘skinned’ muscle fibers • Membranes chemically removed • just protein components left Relative force 1.0 0.01 0.1 1.0 Calcium concentration (mM) Role of calcium Tropomyosin Troponin complex •Troponin and Tropomyosin bind to actin block the actin – myosin binding sites •Troponin is a calcium binding protein • When Troponin binds calcium it moves Tropomyosin away from the actin-myosin binding site Ca Ca Summary • Myosin binds to Actin in ADP/ATPdependent manner • Transition from weak to strong bond rotates myosin head group • Lengthening of the link generates tension • Calcium is required to remove TroponinTropomyosin from the binding sites Where does Calcium come from? • Intracellular storage called Sarcoplasmic Reticulum • Surround each myofibril of the whole muscle • Contains high concentration of calcium • Transverse Tubules connects plasma membrane to deep inside muscle Text Fig 10-21 Myofibril Transverse tubules Sarcoplasmic Reticulum Transverse tubules