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Histo Muscle
Muscle
| Question | Answer |
|---|---|
| Explain skeletal muscle development. | Expression of master control genes (MyoD) occurs in progenitor cells. Stimulation and proliferation of myoblasts into myotubes occurs. Myotubes synthesize specific contractile proteins of the myofibril, developing into the mature skeletal myocytes. |
| Describe the organization of muscle | Sarcomere (contractile unit), myofibril, myofiber (or cell), fascicles, muscle. |
| Describe the different layers of connective tissue that exists around muscle. | Endomysium wraps around muscle cells. Perimysium, wraps around fascicles. Ectomysium, wraps around the whole muscle (fascia lata in the leg). |
| Describe the sarcomere structure. | Runs from z-line to z-line. I-band is a light band between the A-band and the Z-line, on either side of the A-band. The A-band flanks the H-band, which itself flanks the M-line. |
| What types of filaments (cytoskeletal proteins) are located in each band? | Z-line connects the plus ends of actin. I-band only contains actin. A-band contains both actin and myosin. H-band contains myosin only. M-line is were myosin bipolar molecules meet. |
| During contraction, which bands shorten? | Only the I and H bands shorten during contraction |
| What is the sarcolemma? | The plasma membrane of a muscle cell |
| The sarcoplasmic reticulum is analogous to what other structure? | Endoplasmic reticulum |
| What is the triad junction? | It's a junction that is apparent in cardiac muscle cells, where the T-tubules meet at the A and I-bands. |
| What is a diad junction? | It's a junction that is apparent in skeletal muscle cells, where the T-tubules meet at the Z-lines. |
| Thick filament | Composed of bipolar myosin II attached via their tail domains. Each myosin II has two S1 heads that have ATPase activity and contain actin binding sites. Each myosin head is a unidirectional motor protein. |
| Thin filament | Composed of actin globular/G-actin polymerized into filamentous or F-actin. The plus end is capped by Z-capping proteins and is attached to the z-line by alpha-actinin. Polarity of actin changes at the z-line. |
| What is nebulin? | Molecular ruler, determines length of actin filament. |
| Titin | Anchors thick filament in sarcomere, maintains registration, assists in relaxation. |
| Desmin (IF) | Provides mechanical support inside the cell during contraction, links Z-disks between myofibrils |
| Tropomyosin | Long rigid rod --> 1/ 7 actin. Binds troponin and actin |
| Troponin-T | TnT, binds tropomyosin |
| Troponin-I | Inhibitory subunit |
| Troponin-C | Ca2+ binding subunit |
| Explain the role of Ca++ in muscle conraction | Ca++ binding to Troponin-C causes the inhibitory TM-NT complex to move and allow myosin crossbridge binding. The ADP-Pi is released from myosin after the powerstroke conformational change occurs. New ATP binds. |
| Force transmission | Tension is generated by the shortening of sarcomeres in unison. The attachment of terminal sarcomeres with the sarcolemma, ECM, and connective tissue to bone transmits the tension causing movement. |
| Facilitating structures of tension. | Attachment of thin filaments to z-lines and modified terminal z-lines. External basal lamina, tendon, cartilage, fibrocartilage, periosteum, sharpey's fibers. |
| Duchenne Musclular Dystrophy | X-linked recessive; defective dystrophin (homolgous to a-actin); actin binding molecule that attaches actin to the sarcolemma. Without it, muscle damage ensues. |
| T or F. Mature skeletal muscle cells are post-mitotic and have limited generation facilitated by satellite cells? | T |
| The connective tissue layers serve two functions. What are they. | Serve as pathways for blood vessels and nerves. Transmit force from muscle to bone. |
| Sarcoplasm | Cytoplasm |
| How many triads per sarcomere? | 2 |
| Large reservoir of Ca++ in SR bound to.... | Calsequestrin |
| Myosin II molecule | N-term region forms motor domain (ATP&actin binding sites). S1 isolated motor regions. C-term regions from coiled-coiled rod domain. |
| Roughly 300 myosin molecules per thick filament. T or F? | T |
| Barbed end = ______ - end. Pointed end = ________ - end | +;- |
| What are the steps in crossbridge cycle | ATP binding releases myosin cross-bridge cycling. ATP hydrolysis occurs on detatched myosin heaad. Actin binding triggers Pi release, power stroke. |
| How much does a sarcomere shorten? | ~1um |
| Limited capacity for regeneration, no regeneration, and regenerative are associated with what respective muscle types? | Skeletal, Cardiac, and smooth |
| What are the differences between red, white, and pink/intermediate fibers? | R-Contract slowly, but for a long time. Lots of mitochondria+Lipid droplets. Contains myoglobin and & cytochromes. W-contract fast, duration short. E sup. by anaerobic glycolysis. P/I-intermediate interactions. |
| Different myosin isomers have the same effect on muscle contraction speed and duration. T or F. | F, different myosin isoforms have different contraction speed characteristics and duration of contraction capacity. |
| Contraction of the heart is controlled by __________ and excitation spreads intercellularly via __________. | SA nodes; Gap junctions |
| Large, long cylindrical cells with periphery nuclei that look small. What cell type? | Skeletal |
| small, branching cells with centrally located nuclei and abundant mitochondria. What cell type? | Cardiac |
| Gold-like/hot pink-like granules, located close to the nuclei, that contain the undigested lipid and leftover junk in endstage lysosomes. Found in cardiac and nerve cells. | Lipofuscin |
| Intercalated disks are composed of what three structures (transverse and lateral)? | T-Fascia Adherens (modified Z-lines, site of thin filament attachment in terminal sarcomeres, between adjacent cells) and desmosome (att. of IFs). L - gap junctions. |
| Purkinje Fibers | Modified cardiac cells that propagate electrical signals from the AV node to the ventricles. Contain more glycogen granules (PAS stain) and are reduced myofibrils (stain less intensely in H&E). |
| Which muscle cell types contain gap junctions? | Cardiac and smooth |
| Glycogen is present in EMs of cardiac muscles, what do they look like? | Little black dots localized within the sarcomere. |
| What muscle type can be looked at under LM during contraction with obvious changes in nuclei morphology. Describe what the nucleus looks like. | Smooth muscle; nuclei takes on a corkscrew shape. |
| Actin is one of the most abundantly expressed cellular proteins with 10% (non-muscle - 2 genes) and 1-5%(muscle - 4genes). T or F. | F, reversed percentages |
| What complex is important in regulating actin assembly? | Arp2/Arp3 complex |
| What is the difference between G-actin and F-actin. | G-is in globular state bound by either adp or atp. F-is in a filament formation that occurs by the polar assembly of the faster + end. |
| Actin assembly is biphasic, how? | Slow nucleation, but a faster elongation phase. |
| Dense bodies are... | Site to thin filament attachment to the sarcolemma or cytoplasmic a-actin and desmin |
| Actin network in non-muscle as compared to muscle cells differs how? | Non-muscle its more dynamic; muscle cells its more stable. |
| The rate constants for depolymerization of the - end and the polymerization of the + end are __________. | Equal |
| Unlike MT, actin minus ends and plus ends assemble and disassemble at about the same rate. The causes the actin filaments to undergo the ___________ movement. | Treadmilling |
| Most actin-F subunits are have ADP bound, since after polymerization ATP hydrolyzes. However, a significant presence of actin-F bound to ____ exist on the + end, a structure that's often called ________. | Plus; Actin-ATP cap. |
| What is the role of the actin-spectrin network in RBC's | Protects against mechanical damage |
| Microvilli are composed of 20-30 __ filaments, which are cross-linked by __. | Actin; villin and fimbrin |
| An isoform of myosin II, _______, is specialized in that with its tail end it is attached to the _______. | Myosin I; plasma membrane |
| What are the the relevant functions of myosin I? | To deliver new PM from cell body to microvilli and to drive the shedding of enzyme filled vesicles from the cell to the gut. |
| The orientation of actin filaments in the microvilli are the _______ end is at the tip of the villi and the ______ end is at the base. | + (barbed); - (sharp) |
| The + (barbed) end of actin is anchored to the PM by ______ and _______. | CapZ and a-actinin. Similar to the Z-lines. |
| Actin filaments extend their ____end into the terminal web,where ______ motor protein resides. | -; Myosin II |
| T of F. Only myosin II can form thick filaments. | T |
| ___ are modified cilia located in the ear. Cilia Length dictates their frequency determination. | Stereocilia |
| Mutations in myosin ______ can cause deafness. | I, VI, VII |
| Vinculin | ABP that attaches to a-actin and CapZ. |
| Talin | ABP that binds vinculin and integrins |
| Integrin | Transmembrane protein that is bound to talin and ECM proteins |
| Fibronectin | Component of the ECM that is bound by integrin? |
| Contractile networks require myosin II action. What are the various types contractile networks seen in the cell? | Smooth muscle contraction; Cytokinesis; apical contraction of epi sheets (development)Phagocytosis |
| In contractile networks, the myosin II filament is assembled as a response to cell signals. T or F? | T |
| Cellular motility is mediated by... | Contractile network at the rear, a stable network at the site of attachment, and a dynamic network at the leading edge of the cell. |
| The leading edge of a moving cell depends on the__________mediated by signal molecules at the cell surface. | Actin assembly |
| Listeria bacterium use a WASP analogue___ to stimulate actin polymerization to provide it locomotion. | Act A |
| _____ proteins are activated by intracellular signals and stimulates the Arp2/3 complex to nucleate actin assembly. | WASP |
| The ARP 2/3 complex plays a role in actin nucleation by... | Cap point ends of actin; weak nucleator of actin barbed end; crosslinking growing filaments to sides of others at a 70 deg. angle. |
| CapZ | Caps the barbed end |
| ADF/cofilin | severs old filaments to regenerate pool of actin-ADP |
| Profilin | Monomer binding protein that promotes nucleotide exchange from ADP --> ATP. |
| Phallodion | prevents filament disassembly. |
| Cytochalasin | Binds to + end and inhibits further subunit addition |
Created by:
jgenere
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