BIOL 3151: Principles of Animal Physiology

ANIMAL PHYSIOLOGY BIOL 3151: Principles of Animal Physiology Dr. Tyler Evans Email: tyler.evans@csueastbay.edu Phone: 510-885-3475 Office Hours: M,W 10:30-12:00 or appointment Website: http://evanslabcsueb.weebly.com/

PROBLEM SET #1 IN-CLASS ASSIGNMENT WED OCT 16 • will test on Lectures 1-9 • will be in similar format to the midterm exam you will take on Fri Oct 18th • can use notes, textbook and discuss answers with classmates • bring notes from all lectures • have the entire class to complete the assignment

LAST LECTURE CELLULAR MOVEMENT AND MUSCLES MICROTUBULES • cells use this microtubule network to control the movement of vesicles and other cargo to different parts of the cell • e.g. color change in camouflaged animals • Xenopus frog darkens its skin by transporting pigment granules from the MICROTUBULE ORGANIZING CENTER to the periphery of the skin along microtubules Textbook Fig 5.3 pg 200

LAST LECTURE CELLULAR MOVEMENT AND MUSCLES MICROTUBULES • squid chromatophores use the same mechanism • use the polarity (charge difference) between the each end of the microtubule to determine in which direction the pigment granules move (i.e. toward or away from skin)

LAST LECTURE CELLULAR MOVEMENT AND MUSCLES TRANSPORT USING MICROTUBULES • motor proteins recognize this polarity and each motor protein moves in a characteristic direction: • KINESIN: moves along the microtubule in the POSITIVE direction • DYNEIN: moves along the microtubule in the NEGATIVE direction KINESIN DYNEIN

LAST LECTURE CELLULAR MOVEMENT AND MUSCLES TRANSPORT USING MICROTUBULES e.g. neurotransmitters transport down axons • neurotransmitters are released at synapses to induce a response • neurotransmitters are carried from the cell body (i.e. soma) down the axon on microtubules • kinesin can transport neurotransmitters to the end of the synapse (+ direction) • dynein then carries the empty synaptic vesicle back to the soma (- direction) textbook Fig 4.16 pg 162 textbook Fig 5.7 pg 204

LAST LECTURE CELLULAR MOVEMENT AND MUSCLES MICROFILAMENTS • microfilaments are the other type of cytoskeletal element used in movement • also involved in transport within cells, but in cell shape changes and moving from place to place • microfilament based movement uses ACTIN and the motor protein MYOSIN • microfilaments are composed of long string of ACTIN • microfilaments form in much the same way microtubules: “+” and “-” ends of actin assemble • actin monomers are termed G-ACTIN • “G” stands for globular • referred to as F-ACTIN when in polymers • “F” stands for filamentous

LAST LECTURE CELLULAR MOVEMENT AND MUSCLES SLIDING FILAMENT MODEL • the myosin molecule extends by straightening its NECK (i.e. arms extending) • the myosin HEAD then forms a bond with the actin filament (i.e. hands grasping onto the rope) • this strong interaction between actin and myosin is called a CROSS BRIDGE • myosin bends and pulls the actin filament towards its tail (i.e. pull up) • this step is called the POWER STROKE • HEAD then uncouples from actin and myosin returns to the resting unattached position Actual movement depends on whether it is actin or myosin that is free to move • Textbook Fig 5.12 pg 209 • if rope attached, you will pull yourself (myosin is mobile) • If rope not attached, you will pull the rope (actin is mobile)

TODAY’S LECTURE MUSCLE STRUCTURE AND REGULATION OF CONTRACTION • large forces generated during muscle contraction are the result of combining the actions of many polymers of myosin • polymers of myosin are called THICK FILAMENTS • thick filaments are doubled headed, meaning they have clusters of the myosin head at each end • in muscle tissue, thick filaments of myosin slide along polymers of actin called THIN FILAMENTS textbook Fig 5.15 pg 212

MUSCLE STRUCTURE • in vertebrate STRIATED MUSCLE, thick and thin filaments are arranged in a characteristic pattern • cardiac (heart) and skeletal muscles are examples of striated muscle STRIATED MUSCLE textbook Fig 5.16 pg 213

MUSCLE STRUCTURE • basic unit of striated muscle is called the SARCOMERE • muscles are comprised of many sarcomeres arranged in a repeated pattern, that gives striated muscle striped appearance SARCOMERE textbook Fig 5.17 pg 215

MUSCLE STRUCTURE • areas occupied by thick filaments appear darker than those lacking thick filaments • area occupied by thick filaments called the A-BAND • lighter regions are areas lacking thick filaments and are comprised of thin filaments and other cytoskeletal proteins • this region is referred to as the I-BAND • middle region where forming gap between extending thin filaments forms the M-LINE • Z-DISKS are plates that hold actin think filaments in place myosin actin Z-disk M-line

MUSCLE STRUCTURE • basic unit of striated muscle is called the SARCOMERE • sacromere is formed by a thick filament surrounded by an array of six thin filaments • at each end of the sacromere is a protein plate called the Z-DISK • thin filaments extend out from the Z-disk • the double headed thick filaments are arranged between the two Z-disks • thick filaments span two sets of thin filaments, so that one end of the thick filament can associate with one set of thin filaments and the other end with another set of thin filaments textbook Fig 5.18 pg 215

MUSCLE STRUCTURE textbook Fig 5.17 pg 215

MUSCLE STRUCTURE CHANGES IN ACTIN AND MYOSIN DURING MUSCLE CONTRACTION • many myosin molecules extend their necks and attach to actin to form a CROSS BRIDGE • hydrolysis of ATP provides energy for POWER STROKE that pulls thin filaments, which are attached to Z-disk, toward the M-line • as a result, the sarcomere shortens or the muscle contract

MUSCLE STRUCTURE & CONTRACTION FORCE CHANGES IN ACTIN AND MYOSIN DURING MUSCLE CONTRACTION • the arrangement of the sarcomere determines contraction force • if the sarcomere is too short, thin filaments will collide and there will be little space for the muscle to contract • the force generated will decrease Normal Sarcomere Too Short Sarcomere textbook Fig 5.17 pg 215

MUSCLE STRUCTURE & CONTRACTION FORCE CHANGES IN ACTIN AND MYOSIN DURING MUSCLE CONTRACTION • if sarcomere is too long, some myosin heads will not overlap with thin filaments and be unable to form cross-bridges • fewer cross-bridges means less force generated during contraction Normal Sarcomere Too Long Sarcomere textbook Fig 5.17 pg 215

MUSCLE STRUCTURE • the arrangement of the sarcomere effects contraction force textbook Fig 5.19 pg 216

MUSCLE CELL STRUCTURE • muscle cells incorporate hundreds of thousands of repeating sarcomeres • a single continuous stretch of interconnected sarcomeres is called a MYOFIBRIL • MUSCLE CELLS are made of groups of myofibrils encased in a plasma membrane called a SARCOLEMMA

REGULATION OF MUSCLE CONTRACTION • first steps toward muscle contraction occur when action potentials from the brain travel down motor neuron to the neuromuscular junction • this triggers release of neurotransmitter ACETYLCHOLINE, which binds to a receptor on the sarcolemma (muscle cell membrane) • this binding induces an action potential to spread throughout the muscle cell textbook Fig 4.16 pg 162 textbook Fig 5.7 pg 204

REGULATION OF MUSCLE CONTRACTION • action potential generated when ACETYLCHOLINE binds to receptors spreads across the SARCOLEMMA (muscle cell membrane) • the sarcolemma has a unique feature important for contraction • it is covered with pores called T-TUBULES that provide a pathway for action potentials to spread across the muscle cell • as the action potential spread across the muscle cell, it causes large amounts of calcium (Ca+2) to be released from storage units called the SARCOPLASMIC RETICULUM (in blue below)

REGULATION OF MUSCLE CONTRACTION • the released Ca+2 is then used to regulate actin-myosin binding • the Ca+2signal is transmitted to actin and myosin by two proteins that associate with the actin thin filaments: TROPONIN and TROPOMYOSIN • when intracellular Ca+2 is low the complex of troponin and tropomyosin block myosin binding sites on the thin filament • increases in intracellular Ca+2 causes complex of troponin and tropomyosin to roll out of the way and allow myosin to bind to actin filament textbook Fig 5.21 pg 220

REGULATION OF MUSCLE CONTRACTION • TROPONINis composed of three subunits (i.e. smaller proteins that group together to form one large protein) • TnC- is a Ca+2 sensor and can bind Ca+2 with high affinity • TnI- blocks the myosin binding site • TnT- binds tropomyosinand keeps complex associated with actin C = calcium I = inhibitory T = tropomyosin textbook Fig 5.21 pg 220

REGULATION OF MUSCLE CONTRACTION • in a typical muscle cell, intracellular Ca+2 is very low and binding site on TnC are empty. • empty TnC interacts with TnI to block myosin from binding to actin • when muscle is activated, intracellular Ca+2 spikes (100-fold) and binds to TnC • binding of Ca+2 to TnC induces a change in conformation in TnI that exposes the myosin binding site on actin • because TnT is bound to tropomyosin the complex exposes the myosin binding site by sliding down tropomyosin ACTIVE INACTIVE Troponin complex (TnC, TnI, TnT) Myosin head = exposed myosin binding site tropomyosin actin textbook Fig 5.22 pg 220

REGULATION OF MUSCLE CONTRACTION SLIDING FILAMENT MODEL • the myosin molecule extends by straightening its NECK (i.e. arms extending) • the myosin HEAD then forms a bond with the actin filament (i.e. hands grasping onto the rope) • this strong interaction between actin and myosin is called a CROSS BRIDGE • myosin bends and pulls the actin filament towards its tail (i.e. pull up) • this step is called the POWER STROKE • HEAD then uncouples from actin and myosin returns to the resting unattached position Actual movement depends on whether it is actin or myosin that is free to move • Textbook Fig 5.12 pg 209 • if rope attached, you will pull yourself (myosin is mobile) • If rope not attached, you will pull the rope (actin is mobile)

REGULATION OF MUSCLE CONTRACTION • actin-myosin activity stops when action potentials from brain stop and intracellular Ca+2 falls back to resting levels • causes Ca+2binding sites on TnCto be vacant again • myosin binding sites in actin are once again blocked by TnI Ca+2 and myosin binding textbook Fig 5.22 pg 220

REGULATION OF MUSCLE CONTRACTION • this relaxation phase is dependent on ACETYLCHOLINESTERASE, that breaks the down acetylcholine to acetic acid and choline • this stops action potential from triggering the release of Ca+2 from sarcoplasmic reticulum

LECTURE SUMMARY • large forces generated during muscle contraction are the result of combining the actions of many polymers of myosin (THICK FILAMENTS) and actin (THIN FILAMENTS) • basic unit of striated muscle is called the SARCOMERE, which is highly patterned and gives this type of muscle its striped appearance (know the structure) • binding of acetylcholine to its receptor causes action potential to spread across muscle cell membrane called the SARCOLEMMA • aided by pores called T-TUBULES • striated muscle contracts when action potential causes calcium (Ca+2) levels increase within the myofibril • the Ca+2 signal is transmitted to the contractile apparatus by two proteins associated with thin filaments: TROPONIN and TROPOMYOSIN • this relaxation phase is dependent on ACETYLCHOLINESTERASE that stops action potential from triggering the release of Ca+2 from sarcoplasmic reticulum

NEXT LECTURE MUSCLE DIVESITY IN VERTEBRATES AND INVERTEBRATES textbook Fig 5.34 pg 239

BIOL 3151: Principles of Animal Physiology