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

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Taste Smell

Long distance Many receptors –1000s mouse – 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 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

Sensory neuron depolarization Ca ++ Na + Complex stimuli Sugars Bitter Ionic stimuli Salt (Na+) Sour (H+) Second messenger Intracellular Ca ++ Taste Receptor

Olfaction Press Release: The 2004 Nobel Prize in Physiology or Medicine 4 October 2004 The Nobel Assembly at Karolinska InstitutetThe 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"

ATP cAMP Odourant molecule G-protein receptor Na+

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 Smooth Skeletal movement Cardiac heart Blood vessels lungs intestine Mechanisms of muscle contraction essentially the same Differences in how muscle cells are organized and how contractions initiated

Muscle Tendon Bone Muscle Fibers nucleus Myofibril Skeletal muscle

Z ZZ M Sarcomere (2-3  m) A band I H Myofibril band zone

Banding patterns due to overlapping protein filaments H A I Z disk Actin filament Myosin filament Actin filament ‘cross bridges’

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

Stimulator Sarcomere length (  m) Relative tension Control muscle length Length – Tension relationship for single sarcomere Measure tension

Sarcomere length (  m) Relative tension

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 Myosin Light Chains S2 Link

protein filaments of the sarcomere Actin filament Myosin filament Actin filament ‘cross bridges’

Myosin filament ~150 cross-bridges at each end of the myosin filament Myosin self-assembles into filaments

Actin filaments F-Actin (flimanetous) assembles from G-actin (globular) Actin has myosin binding sites

Myofilament chemistry Actin + myosin  Actomyosin complex Actin + myosin  Actomyosin complex ATP

Myosin-ATP  Myosin-ADP-Pi  Myosin +ADP +Pi Myosin-ADP-Pi + Actin  Actomyosin + ADP + Pi Very slow! Very fast! Releases energy  Actin  rate of ATP hydrolysis by myosin

Myosin-ADP-Pi binds Actin weakly Myosin-ADP Head rotates ADP is released and ATP binds Myosin Myosin-ATP released from Actin Myosin hydrolyzes ATP  ADP+Pi Myosin-ADP binds Actin strongly Pi Myosin-ATP Actin-Myosin Cycle

Transition between weakly bound and strongly bound complex generates tension

Myosin filament Myosin head group S2 link Actin filament Binding sites Stretching of the link generates tension Weak binding Strong binding

Equal and opposite force on thick filament Why do thin filaments move? Net force

Actin + myosin  Actomyosin complex ATP What if we don’t have this? X Rigor mortis

Role of calcium Intracellular Calcium is required for muscle contraction Used ‘skinned’ muscle fibers Membranes chemically removed just protein components left Calcium concentration (mM) Relative force

Role of calcium Troponin complex Tropomyosin 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

Summary Myosin binds to Actin in ADP/ATP- dependent manner Transition from weak to strong bond rotates myosin head group Lengthening of the link generates tension Calcium is required to remove Troponin- Tropomyosin 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 Myofibril Sarcoplasmic Reticulum Transverse tubules