1 Exam 2 KEY plus extra detail BIO 361T Fall 2014 1 Name Discussion circle one M2 00 M3 00 T2 00 T3 30 Each muscle is a group of muscle cells myocytes that are connected Smooth and cardiac muscles are held together via gap junctions while skeletal muscles are held together by only connective tissue Muscle cells have cytoskeletal networks of actin and myosin proteins that allow them to change shape comprising thin and thick filaments respectively In striated muscle these filaments are arranged into sarcomeres which are connected to form myofibrils that run the length of the cell 10 points 2 Draw a molecular model of how a skeletal muscle fiber contracts from neurotransmitter binding to fiber shortening Clearly indicate two points at which this differs from smooth muscle and what the differences are 10 points 0 5 ACh binds receptor could be different NT receptor in smooth muscle 1 Sarcolemma or cell membrane depolarizes via voltage gated Na K channels spreads down T tubules no T tubules in smooth cells are connected by gap junctions 1 Opens voltage gated Ca2 channel in sarcolemma DHPR 1 Connected to SR Ca2 channel RyR which also opens not in smooth little SR in smooth 1 Ca2 floods sarcoplasm 1 Ca2 binds troponin Ca2 binds calmodulin 1 Tropomyosin moves off of myosin binding site Moves caldesmon off of site 1 Myosin head hydrolyzes ATP uses energy to extend head and bind actin releasing ADP and Pi 0 5 Myosin head pulls actin shortening the sarcomere not organized into sarcomeres fibers 1 difference between smooth and skeletal 3 Explain how a myocyte can be modified to primarily generate heat as in the billfish heater organ 3 points Reduce contractile properties few myofibrils Increase Ca2 pumping which increases sugar catabolism and other steps of ATP production cellular respiration which is exothermic lots of SR and mitochondria Not to be confused with the electric organ where many myocytes fuse together and lose contractility but maintain excitable membrane properties to fire electric discharge 4 Choose one category of taste salty sour bitter sweet that vertebrates can detect and explain the molecular mechanism of gustation 5 points 2 Salty Na enters Na channel depolarization opens voltage gated Ca2 channel releases NT onto sensory afferent sends input to brain Sour H binds a channel in humans binds and closes a K channel depolarization same as above Bitter tastant binds GPCR activates G protein transducing 2nd messenger cascade opens Ca2 channel same as above Sweet sugar molecule binds GPCR activates G protein gustducin 2nd messenger cascade cAMP closes K channel depolarization opens voltage gated Ca2 channel same as above Remember that the taste receptors are modified epithelial cells they do not fire action potentials themselves 5 How does the vertebrate auditory system detect and transduce the volume of a sound 5 points Pressure wave has higher amplitude which bends hair cells in inner ear more Opens more mechanically gated K channels More K comes in greater depolarization More voltage gated Ca2 channels open more neurotransmitter released Greater frequency of action potentials fired by sensory afferent to brain 6 Why can vertebrates see with higher resolution in daylight than in low light levels 6 points Because their cones are active in daylight where there is little convergence unlike rods Each photoreceptor synapses onto one bipolar cell which synapses onto one ganglion cell Only rods are active in low light which are at a low concentration in the fovea resulting in a lowresolution image Not because vertebrates have high cone rod ratio overall which was a common answer Ratio overall varies among vertebrates depending on diurnal vs nocturnal Vertebrates animals 7 Use a table to compare and contrast the statocyst system in cephalopods to the vestibular system in vertebrates 4 points Statocysts in cephalopods System of tubes at different angles Lined with mechanoreceptors Detect orientation and movement Contain statoliths Vestibular system in vertebrates System of tubes at different angles Lined with mechanoreceptors Detect orientation and movement Contain otoliths 8 What part of a bat s echolocation call is used for long range searching and accounting for velocity of moving targets 2 points a Constant frequency b CF sweep c Frequency modulated d FM pulse 9 What part of a bat s echolocation call is used for short range homing and accurately estimating distance to a target 2 points a Constant frequency b CF sweep c Frequency modulated d FM pulse 10 Give a detailed molecular explanation of how a serotonin receptor antagonist inhibits sensitization of the gill withdrawal reflex in Aplysia 8 points 3 When tail is shocked sensory afferent causes interneuron to release serotonin onto axon terminal of siphon sensory afferent Antagonist is bound to serotonin receptor preventing serotonin from binding Will not cause gill to be withdrawn more in response to tail shock which is due to binding GPCRs Will not activate second messenger cascades adenylate cyclase cAMP and PLC DAG PKC that prolong depolarization by inhibiting K channels and increase Ca2 by opening more voltagegated Ca2 channels and other Ca2 channels Will not increase NT release onto gill motor efferent 11 Why is the CA3 CA1 hippocampal pathway a good cellular model for learning Include a basic molecular mechanism 5 points Because CA1 remembers previous activation via LTP If CA3 is repetitively stimulated it will release more Glu onto CA1 which will increase CA1 s sensitivity to Glu and Glu release by CA3 in the future 12 True or False If false give a counter example 3 points a All chordates are vertebrates False sea squirts tunicates b All vertebrates are chordates True c There are no radially symmetrical Bilateria False echinoderms like star fish d Adult lampreys jawless fish have notochords True visible in specimen we saw 13 Explain two features of smooth muscle that make it more suited for blood vessels than cardiac or skeletal muscle 6 points Filaments arranged in multiple directions which allows it to contract and withstand stretching in multiple directions Filaments anchored to cell membrane in multiple spots via adhesion plaques which allows it to contract and withstand stretching in multiple directions Connected by gap junctions which allows multiple muscle cells to contract simultaneously unlike skeletal muscle Can sustain contraction tonically 14 Use two variables to explain why blood flow Q is less in
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