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Cytoskeleton
Medical Cell Biology
Term | Definition |
---|---|
Functions of Cytoskeleton | Provides structural integrity, cell motility/contraction of muscles, change in cell shape, and movement of organelles |
3 Types of Muscle | skeletal, cardiac, and smooth |
Skeletal Muscle | striated, multi-nucleated, consist of actin and myosin |
Sacromere | Functional contractile unit of a skeletal muscle |
3 Layers of connective tissues surround skeletal muscle | Epimysium, Perimysium, and Endomysium |
Epimysium | Surround the whole muscle (group of muscle fasciculi) |
Perimysium | Surround muscle fasciculous (bundle of muscle fibers) |
Endomysium | Surround individual muscle fiber. |
Z Disk | actin thin filaments |
A band | Remain constant during contraction |
I Band | Shortens during contraction |
H Band | Center of A band, overlapping of thick and thin filament (thick filament) |
M Line | Anchor thick filament (myosin) |
Actin | composed of F-actin (polymerize) and G actin (globular protein) |
What is important about the G-protein? | Binds to ATP to polymerize F-actin. Polymerization: need ATP and Mg2+ |
Tropomyosin | Wrap around the thin filament |
Troponin | Bind to tropomyosin (block the myosin head binding site) TnC, TnI, TnT |
Tropomodulin | Cap slow growing end (-) |
Polymerization of actin | Lag phase, polymerization phase, and Steady Phase, |
Steady Phase | Also known as tread milling Effect. Monomers added is equal to the number of monomers removed. Addition of G-actin ATP (+ end) = loss of G-actin ADP (-end) |
Tropomyosin | Wrap around the thin filaments for stability of F-actin |
Z disk proteins | Cap Z and alpha actinin (anchored thin filament) |
Cap Z | bind to + end of F-actin prevent growth and depolymerization |
Alpha actinin | Space b/w thin filaments so thick filaments won't bind |
Titin | Keep myosin thick filament centered |
Nebulin | extended from Z-disk to (-) end of thin filament |
Desmin | Stabilize the Z-disk |
Myosin | consists of 2 heavy chains and 2 light chains. Formed in coiled-coil helix fashion with a repeat sequence of amino acids- to avoid aqueous solution |
Papain | Cleave myosin heads |
Rigor Mortis | Occurs when there is no ATP. The myosin head remain binding to the actin filament - Stiffness |
Calcium regulation | Troponin complex bound to tropomyosin, block the binding site for myosin head. |
What happens when Ca binds to Troponin C? | Moves troponin away from the tropomyosin. This exposes actin to the myosin head |
Sarcroplasmic Reticulum | Stores Ca++, consists of 2 terminal cisternae and one T-tubule (triad) |
DHPR (Dihydropyridine receptor) | Locates along the T-Tubule, which will undergoe a conformational change. |
Ryanodine receptor | Ca2+ channel of the SR. This SR Ca2+ channel open and release Ca2+ into the cytosol |
Calsequestrin | Takes back Ca into the SR by Ca2 ATPase |
Cardiac Muscle Cell | Location of the nuclei is in the center where as the location of the nuclei in a skeletal muscle is in the periphery. Contraction is the same as skeletal muscle |
Intercalated disks | Only present in Cardiac cells |
Gap Junctions | Located in intercalated disks. It is for synchronizing the contraction (allow rapid exchange of solutes and ions) |
Desmosome (macula adherens) | Hold cells together |
Fascia adherens | Hold actin thin filament together like Z-disk |
Familial Hypertrophy Cardiomyopathy | Defect in cardiac B-myosin |
Familial Dilated Cardiomyopathy | Defect in cardia a-actin |
Smooth Muscles | No sarcomere, no troponin, not striated. Has dense bodies, lots of IFs (desmin, vimentin). Ratio of thin to thick 12:1. Made up of Dense bodies |
Dense Bodies | Made up of a-actinin |
Myosin Light Chain Kinase | Phosphorylates Myosin Light chain |
Ca2+ Calmodulin - Contraction | Myosin light chain kinase is inactive when Ca-calmodulin complex form. This will phosphorylate myosin light chain and become active |
Ca2+ Calmodulin - Relaxation | Dephosphorylation of myosin light chain by removing pi by phosphatase |
Catcholamine | Binds to Beta adrenergic receptors. Cause an increase in cAMP, which phosphorylates protein Kinase A |
Protein Kinase A | Phosphorylates myosin light chain kinase - cause inability to bind to calmoduline-- lead to relaxation |
Dephosphorylation of MLCK | Causes muscle to contract by dephosphorylation of MLCK. MLCK is active |
release of Ca+2 and DAG is stimulated by which kinase? | Protein kinase C |
Caldesmon | Ca+2 proteins that interact with actin thin filaments |
Contractile Ring | Present during telophase of mitosis. During mitosis, actin filaments form at cleavage site-cleavage furrow. Myosin polymerises with actin contractile ring |
Villin and fimbrin | Bundled together and then attach to microvilli. Increase surface area for absorption at + end |
Spectrin II and Myosin II | Link two bundles together at terminal web. Microvilli anchored at terminal web. |
Gelsolin | Keep cytosol liquification that is triggered by increased calcium. Makes fragment filaments |
Profilin | Polymerization. When PIP2 is bound to profilin, profilin cannot bind to actin. When PIP2 hydrolyzes to IP3 and DAG by PLP-C release profilin |
Thymosin | Binds to G-actin and keep it in that state |
Cytochlasin | Inhibitors of actin filament. Blocks plus end |
Paballoidin | Stabilize microfilament does not allow depolarization |
Protrusion | Actin polymerization. If polymerization is greater than retrograde flow = cell protrusion |
Retrograde flow | myosin II contractile |
Arp 2/3 nucleating complex | Branching of lamellipodia |
Lamellipodia and filopodia | extension at leading edge for cell movement |
WasP and Scar | Binds to Arp 2/3 - promote actin polymerization |
Cdc42 | Activate Scar bind to Arp 2/3 form filopodia |
Rac | Activate Wasp and PI (4) P5 kinase form lamellipodia and membrane ruffles |
Rho | Bundling of actin with myosin II. |
Rhokinase | Phosphorylates myosin II--contracation |
ERM proteins | Ezrin, Radixin, Moesin |
Defect Merlin | Leads to Neurofibromatosis |
What attaches actin filament to plasma membrane | ERM Proteins |
Spectrin 4.1 | Maintains biconcave shape of RBC |
Ankyrin | Anchored spectrin to membrane. The whole complex is stabilized by protein 4.1 |
Ubiquination | Is needed for shaping RBC |
Dystrophin | Protein that belong to spectrin gene family. If absent - responsible for Duchenne's Muscular Dystrophy |
Intermediate filaments | Resistance to mechanical stress. (ankyrin and spectrin II) |
Keratin filament | Epithelial Cells |
Neurofilament | Neurons |
Vimentin | Containing filaments - fibroblasts/glial cells/ muscle cells |
Nuclear Lamina | All nucleated cell (except RBC) |
GFAP | brains |
Microtubules | Need tubulin alpha and beta. 13 protofilament. Flagella and cilia motility, Meitotic and mitotic spindles. Vesicle transport. Need GTP |
Drugs that Target Microtubules | Colchine, Viblastine sulphate, Nocodazole, Paclitaxel |
Polarity | addition of subunit is faster at (+) end, (-) end is capped due to centrosome complex |
Centrosome complex | Composed at 9 short-triplet microtubules (9+2 arrangement) |
Kinesin | Anterograde transport (-end to +end) |
Dynein and KRPS | Retrograde transport + end to - end |
Dynactin Complex | Arp 1, Spectrin, Dynein |
APP (Amyloid Precursor Protein) | Defect in MAMR (membrane associated motor receptors causes Alzheimer's disease |
Dynein | ATPase extending towards B Tubule |
Nexin | Attaches neighboring doublets |
Radial Spokes | Attach doublets to the center |
Arrangement of Microtbules in cilia and flagella | Arranged in 9+2 array. Doublet alpha tubule and beta tubule |
Metaphase | Chromosome line in the middle - 2 forms: interpolar (overla of the spindles) and ASTRAL (GROWING AWAY FROM THE KINETOCHORE) |
Telophase | Cytokinesis (contractile ring) - form daughter cell membrane |
MAPs and Tau | Bind to tubulin monomoer of microtubule-allow bundling and stabilize MT |
MAPs (EB 1 and CLIP 170) | Attach MT to kinetochore |
Katanins and Stathmins/Op18 | Disrupt microtubules formation |
Katanins | Prevent the additions of tubulins to MTs by binding to tubulins dimer |
Stathmin | Detach MTs from MTOC |