aravind cell bio.pptx ............................................

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1. 1 CYTOSKELETON CYTOSKELETON

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3. https://www.slideserve.com/shawna/cell-analogy-analogy-to-a-school https://prezi.com/4zgst85do-t2/cell-analogy-project-house/ 3

4. How and Why Cells Move 4 https://www.thoughtco.com/how-and-why-cells-move-373377 In cases involving wound injury and repair, connective tissue cells must travel to an injury site to repair damaged tissue.  White blood cells, such as neutrophils and macrophages must quickly migrate to sites of infection or injury to fight bacteria and other germs. Cancer cells have the ability to metastasize or spread from one location to another by moving through blood vessels and lymphatic vessels- Epithelial to Mesenchymal Transition (EMT) In the cell cycle, movement is required for the cell dividing process of cytokinesis to occur in the formation of two daughter cells. Movement within the cells Vesicle transportation Organelle migration Chromosome movement during mitosis  

5. 5 https://scienceaid.net/the_Eukaryotic_Cell_Cytoskeleton

6. Actin filaments determine the shape of the cell’s surface and are necessary for whole-cell locomotion; they also drive the pinching of one cell into two. Microtubules determine the positions of membrane-enclosed organelles, direct intracellular transport, and form the mitotic spindle that segregates chromosomes during cell division. Intermediate filaments provide mechanical strength . 6

7. https://mmegias.webs.uvigo.es/02-english/5-celulas/7-citoesqueleto.php https://kaylasanatomyclass.weebly.com/cytoskeleton.html http://www.nslc.wustl.edu/courses/bio101/cruz/Organelles/Organelle.htm 7 https://gfycat.com/gifs/search/cytoskeleton https://alg.manifoldapp.org/read/fundamentals-of-cell-biology/section/301523e1-6d5d-488f-8dce-e73b46200340

8. Distribution of actin in the cell 8 https://www.mechanobio.info/cytoskeleton-dynamics/what-is-the-cytoskeleton/what-are-actin-filaments/how-are-actin-filaments-distributed-in-cells-and-tissues/

9. Microfilaments 9 https://www.mdpi.com/2073-4409/9/2/358/htm https://onlinelibrary.wiley.com/doi/full/10.1002/rmb2.12316

10. 10 https://lizawolfson.co.uk/portfolio-item/animated-gifs/ The two ends of an actin filament grow at different rates, with monomers being added to the fast-growing barbed end five to ten times faster than to the slow-growing pointed end.

11. Treadmilling Treadmilling- Simultaneous gain of monomers from + end and loss of monomers from – end, maintaining the length of the actin. Rate of gain and loss of the filament is the same. However, the monomer moves through the filament. The monomer that is added at the + end ultimately reaches the - end and falls off at the – end. 11 https://www.memorangapp.com/flashcards/170868/Lecture+3%3A+Actin/ Intermediate concentrations of Actin

12. Initiation of actin filaments-Nucleation Formins are a family of large (140-200 kd) barbed-end tracking proteins that both nucleate the initial actin monomers and then move along the growing filament, adding new monomers to the barbed end. 12 https://www.mechanobio.info/cytoskeleton-dynamics/what-is-the-cytoskeleton/what-are-actin-filaments/how-does-arp23-mediate-the-nucleation-of-branched-filaments/

13. 13 F ormin homology (FH) GTPase binding domain (GBD) Dia-autoregulatory domain (DAD) Diaphanous inhibitory domain (DID)

14. 14 Arp-Actin related protein

15. 15 Arp-Actin related protein

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17. 17 https://www.mdpi.com/2073-4409/9/2/358/htm Wiskott–Aldrich Syndrome protein (WASP)

18. ADF/Cofilin (Actin depolymerizing Factor) 18 https://www.semanticscholar.org/paper/Taurine-chloramine-induced-inactivation-of-cofilin-Luo-Uehara/fa1fbcd967ff6b6005fc62708e5d96fe2ff80be5

19. Depolymerisation ADF/cofilin (Actin depolymerizing Factor) These proteins bind to actin filaments and enhance the rate of  dissociation of actin/ADP monomers from the pointed end. ​ ADF/cofilin can also sever actin filaments. ADF/cofilin preferentially binds to ADP-actin, so it remains bound to actin monomers following filament disassembly and sequesters them in the ADP-bound form, preventing their reincorporation into filaments. ​ Profilin acts by stimulating the exchange of bound ADP for ATP, resulting in the formation of actin/ATP monomers, which dissociate from cofilin and are then available for assembly into filaments. ​ 19

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21. Polymerisation- Profilin 21

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23. Bundles 23 https://iopscience.iop.org/book/978-0-7503-1753-5/chapter/bk978-0-7503-1753-5ch7 Supports projections of the plasma membrane, such as microvilli.​ Fimbrin is a 68 kd protein containing two adjacent actin-binding domains. It binds to actin filaments as a monomer, holding two parallel filaments close together. (14nm) The second type of actin bundle is composed of filaments that are more widely spaced, allowing the bundle to contract. (40nm) Alpha-actinin binds to actin as a dimer, each subunit of which is a 102 kd protein  containing a single actin-binding site. 55kDa globular protein that is a component of the crosslinking actin filaments functional module. Fascin organizes F-actin into tightly packed parallel bundles approximately 8nm apart.

24. Actin Network 24 https://www.mechanobio.info/cytoskeleton-dynamics/actin-crosslinking/

25. Extracellular Matrix 25

26. Extracellular matrix 26

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30. 30 https://www.researchgate.net/figure/Epithelial-cell-cell-and-cell-matrix-junctions-Schematic-drawing-of-key-epithelial_fig1_298739733

31. Cultured fibroblasts secrete extracellular matrix proteins that stick to the surface of the culture dish. The fibroblasts then attach to this extracellular matrix on the culture dish via the binding of transmembrane proteins (called integrins). The sites of attachment are discrete regions (called focal adhesions) that also serve as attachment sites for large bundles of actin filaments called stress fibers. Stress fibers are contractile bundles of actin filaments, cross-linked by a- actinin and stabilized by tropomysosin, which anchor the cell and exert tension against the substratum. They are attached to the plasma membrane at focal adhesions via interactions with integrin. These complex associations are mediated by several other proteins, including talin and vinculin. For example, both talin and a-actinin bind to the cytoplasmic domains of integrins. Talin also binds to vinculin and both proteins also bind actin. Other proteins found at focal adhesions also participate in the attachment of actin filaments, and a combination of these interactions is responsible for the linkage of actin filaments to the plasma membrane. Cell-Matrix interactions 31

32. The actin cytoskeleton is similarly anchored to regions of cell-cell contact called adherens junctions.  In sheets of epithelial cells, these junctions form a continuous belt-like structure (called an adhesion belt) around each cell in which an underlying contractile bundle of actin  filaments is linked to the plasma membrane.  Contact between cells at adherens junctions is mediated by transmembrane proteins called cadherins. The cadherins form a complex with cytoplasmic proteins called catenins, which associate with actin filaments.  Cell-Cell interactions 32

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35. 35 Pseudopodia are extensions of moderate width, based on actin filaments cross-linked into a three-dimensional network, that are responsible for phagocytosis and for the movement of amoebas across a surface.  Lamellipodia are broad, sheet-like extensions at the leading edge of fibroblasts, which similarly contain a network of actin filaments.  Many cells also extend microspikes or filopodia, thin projections of the plasma membrane supported by actin bundles.

36. 36 https://f1000research.com/articles/4-940

37. Filopodia contains 15-20 parallel filaments tightly packed into bundles with their barbed membrane facing the membrane. 37 Lamellipodium is driven by a growing network of actin microfilaments (branched actin). Arp2/3 and WASP serve as nucleators. ADF, Profilin and capping proteins co-operate to help in treadmilling. https://www.researchgate.net/figure/Two-phases-of-the-Ecoli-movement-The-bacteria-migrates-due-to-movement-of-the-flagella_fig4_228634410

38. 38 https://www.mechanobio.info/cytoskeleton-dynamics/what-are-invadopodia/ Invadopodia Invadopodia are elongated ventral projections that extend into the underlying ECM. Microtubules and intermediate filaments have also been detected in mature invadopodia. Actin filament nucleators and their regulators such as the Arp2/3 complex, N-WASP (neuronal Wiskott-Aldrich syndrome protein), WASP-interacting protein (WIP) and cortactin are also found localized to this structure. Invadopodia contain a substantial number of actin filaments arranged as parallel bundles, akin to those observed in filopodia. Cross-linking proteins such as fascin are abundant in invadopodia

39. 39 https://www.mechanobio.info/cytoskeleton-dynamics/what-are-lamellipodia-and-lamella/what-steps-are-involved-in-lamellipodia-assembly/ First, cells must develop an initial polarity via specialization of the plasma membrane or the cell cortex. Second, protrusions such as pseudopodia, lamellipodia, or filopodia must be extended to establish a leading edge of the cell. These extensions must then attach to the substratum across which the cell is moving. Finally, during cell migration the trailing edge of the cell must dissociate from the substratum and retract into the cell body.

40. 40 A migrating cell needs to perform a coordinated series of steps to move. Cdc42 regulates the direction of migration, Rac induces membrane protrusion at the front of the cell through stimulation of actin polymerization and integrin adhesion complexes, and Rho promotes actin:myosin contraction in the cell body and at the rear. https://www.sciencedirect.com/science/article/pii/S001216060300544X#FIG1

41. 41 Actins in Cancer Progression https://universe-review.ca/R10-39-embo.htm

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43. Degradation of basement membrane Malignant cells generally secrete proteases that digest extracellular matrix components, allowing the cancer cells to invade adjacent normal tissues. Secretion of collagenase, for example, appears to be an important determinant of the ability of carcinomas to digest and penetrate through basal laminae to invade underlying connective tissue 43

44. https://www.omicsonline.org/articles-images/2168-9296-3-137-g002.html 44 Invadopodia in cancer migration. After tumor cells have proceeded through EMT, invadopodia form in the cellular cytoskeleton, giving the cells a migratory phenotype. Degradation of basement membranes and extracellular matrix during migration is achieved by invadopodia through the use of metallo proteases. Cells can then migrate to the ECM, where they form pseudopodia. Invadopodia are involved in directional migration and chemotaxis during the travel through the ECM. Once tumor cells reach the endothelium, they again use invadopodia to degrade the basement membrane and enter the blood stream.

45. Actins in Muscle Contraction 45

46. 46 The core of a Z-disc consists of actin filaments coming from adjacent sarcomeres which are crosslinked by  α  actinin molecules. Mature Z-discs are probably composed of hundreds of different proteins.

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48. Two additional proteins (titin and nebulin) also contribute to sarcomere structure and stability. Titin is an extremely large protein (3000 kd), and single titin molecules extend from the M line to the Z disc. These long molecules of titin are thought to act like springs that keep the myosin filaments centered in the sarcomere and maintain the resting tension that allows a muscle to snap back if overextended. Nebulin filaments are associated with actin and are thought to regulate the assembly of actin filaments by acting as rulers that determine their length. 48

49. The type of myosin present in muscle (myosin II) is a very large protein (about 500 kd) consisting of two identical heavy chains (about 200 kd each) and two pairs of light chains (about 20 kd each). Each heavy chain consists of a globular head region and a long a-helical tail. The a- helical tails of two heavy chains twist around each other in a coiled-coil structure to form a dimer, and two light chains associate with the neck of each head region to form the complete myosin II molecule. The motor activity of myosin moves its head groups along the actin filament in the direction of the barbed end. This movement slides the actin filaments from both sides of the sarcomere toward the M line, shortening the sarcomere and resulting in muscle contraction. 49

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51. In striated muscle each tropomyosin molecule is bound to troponin, which is a complex of three polypeptides: troponin C (Ca2+-binding), troponin I (inhibitory), and troponin T (tropomyosin-binding). 51

52. 52 https://courses.lumenlearning.com/wm-biology2/chapter/atp-and-muscle-contraction/

53. Activation of myosin in smooth muscle and non-muscle cells In non-muscle cells and in smooth muscle, however, contraction is regulated primarily by  phosphorylation of one of the myosin light chains called the regulatory light chain. Phosphorylation of the regulatory light chain in these cells has at least two effects: It promotes the assembly of myosin into  filaments, and it increases myosin catalytic activity enabling contraction to  proceed.  The enzyme that catalyzes this phosphorylation, called myosin light- chain kinase, is itself regulated by association with the Ca2+-binding protein calmodulin.  Increases in cytosolic Ca2+promote the binding of calmodulin to the kinase resulting in phosphorylation of the myosin  regulatory light chain. Increase in cytosolic Ca2+ is thus responsible, albeit indirectly, for activating myosin in smooth muscle and non muscle cells, as well as in striated muscle.  53

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57. Microtubules They function both to determine cell shape and in a variety of cell movements, including some forms of cell locomotion, the intracellular transport of organelles, and the separation of chromosomes during mitosis. Microtubules are composed of a single type of globular protein called tubulin. The building blocks of microtubules are tubulin dimers consisting of two closely related 55 kd polypeptides: α- tubulin and β-tubulin. A third type of tubulin (γ-tubulin) is concentrated in the centrosome where it plays a critical role in initiating microtubule assembly. Tubulin dimers polymerize to form microtubules, which generally consist of 13 linear protofilaments assembled around a hollow core. The protofilaments, which are composed of head-to-tail arrays of tubulin dimers, are arranged in parallel. Consequently, microtubules (like actin filaments) are polar structures with two distinct ends: a fast-growing plus end and a slow- growing minus end. Tubulin dimers can depolymerize as well as polymerize, and microtubules can undergo rapid cycles of assembly and disassembly. 57

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60. In particular, the GTP bound to β -tubulin (though not that bound to a-tubulin) is hydrolyzed to GDP during or shortly after polymerization. This GTP hydrolysis weakens the binding affinity of tubulin for adjacent molecules, thereby favoring depolymerization and resulting in the dynamic behavior of microtubules. 60

61. Treadmilling and the role of GTP in microtubule polymerization Like actin filaments, microtubules undergo treadmilling, a dynamic behavior in which tubulin molecules bound to GDP are continually lost from the minus end and replaced by the addition of tubulin molecules bound to GTP to the plus end of the same microtubule. 61

62. Dynamic instability In microtubules, rapid GTP hydrolysis also results in the behavior known as dynamic instability (described by Tim Mitchison and Marc Kirschner) in which individual microtubules alternate between cycles of growth and shrinkage. Whether a microtubule grows or shrinks is determined in part by the rate of tubulin addition relative to the rate of GTP hydrolysis. As long as new GTP-bound tubulin molecules are added more rapidly than GTP is hydrolyzed, the microtubule retains a GTP cap at its plus end and microtubule growth continues. However, if the rate of polymerization slows, the GTP bound to tubulin at the plus end of the microtubule will be hydrolyzed to GDP. If this occurs, the GDP-bound tubulin will dissociate, resulting in rapid depolymerization and shrinkage of the microtubule. 62

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65. Assembly of Microtubules In animal cells, most microtubules extend outward from the centrosome (first described by Theodor Boveri in 1888), which is located adjacent to the nucleus near the center of interphase (non-dividing) cells.   During mitosis, microtubules similarly extend outward from duplicated centrosomes to form the mitotic spindle, which is responsible for the separation and distribution of chromosomes to daughter cells. Plant cells do not have centrosomes, instead the microtubules extend from the nucleus. 65

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68. γ -tubulin is associated with eight or more other proteins in a ring-shaped structure called the γ-tubulin ring complex.  68

69. 69 https://www.researchgate.net/figure/Model-for-microtubule-assembly-The-g-tubulin-ring-complex-g-TuRC-is-constituted-by-the_fig1_230817995

70. Severing enzymes-Katanins 70 https://onlinelibrary.wiley.com/doi/full/10.1002/cm.21522 Control microtubules (magenta) in the absence of katanin lose dimers from the ends due to normal degradation to replenish the background concentration. This loss of polymer is slow. (middle) In the presence of katanin (green) katanin can catalyze the loss of dimers from both the ends of control microtubules, called depolymerization, and from the middle of control microtubules, called severing. We observe a significant amount of mobility, association, and dissociation of katanin to and from the filaments. (right) Microtubules lacking the CTT can still bind katanin, but fewer katanins are bound and the bound katanin is less mobile. Without the CTT, katanin cannot sever microtubules but can still catalyze the loss of dimers from the ends. CTT, C-terminal tail

71. Organization of microtubules in nerve cells Microtubules in axons and dendrites are organized differently and associated with distinct MAPs. In axons, the microtubules are all oriented with their plus ends away from the cell body, similar to the general orientation of microtubules in other cell types. The minus ends of most of the microtubules in axons, however, are not anchored in the centrosome; instead, both the plus and minus ends of these microtubules terminate in the cytoplasm of the axon. In dendrites, the microtubules are oriented in both directions; some plus ends point toward the cell body and some point toward the cell periphery. These distinct microtubule arrangements are paralleled by differences in MAPs: Axons contain tau proteins, but no MAP-2, whereas dendrites contain MAP-2, but no tau proteins, and it appears that these differences in MAP-2 and tau distribution are responsible for the distinct organization of stable microtubules in axons and dendrites. 71

72. Axons contain tau proteins, but no MAP-2 Dendrites contain MAP-2, but no tau proteins 72 MAP-1, MAP-2, and tau -Neuronal cells MAP-4 - Non-neuronal vertebrate cells Tau- main component of the characteristic lesions found in the brains of Alzheimer's patients.

73. 73 https://www.frontiersin.org/articles/10.3389/fncel.2018.00165/full

74. Microtubule Motors and Movement Kinesins and the dyneins—are responsible for powering the variety of movements in which microtubules participate. Kinesin and dynein move along microtubules in opposite directions—most kinesins toward the plus end and dyneins toward the minus end. Kinesin I is a molecule of approximately 380 kd consisting of two heavy chains (120 kd each) and two light chains (64 kd each). The heavy chains have long a-helical regions that wind around each other in a coiled-coil structure. The amino-terminal globular head domains of the heavy chains are the motor domains of the molecule. They bind to both microtubules and ATP, the hydrolysis of which provides the energy required for movement. The tail portion of the kinesin molecule consists of the light chains in association with the carboxy-terminal domains of the heavy chains. This portion of kinesin is responsible for binding to other cell components (such as membrane vesicles and organelles) that are transported along microtubules by the action of kinesin motors. Cytoplasmic dynein is an extremely large molecule (up to 2000 kd), which consists of two or three heavy chains (each about 500 kd) complexed with a variable number of light and intermediate chains, which range from 14 to 120 kd 74

75. 75 https://biologydictionary.net/neuron/#foobox-7/0/neuronterminal.jpg

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78. Cargo Transport and Intracellular Organization One of the major roles of microtubules is to transport macromolecules, membrane vesicles, and organelles through the cytoplasm of eukaryotic cells. Kinesin and dynein carry their cargoes to and from the tips of the axons, respectively. For example, secretory vesicles containing neurotransmitters are carried from the Golgi apparatus to the terminal branches of the axon by kinesin. In the reverse direction, cytoplasmic dynein transports endocytic vesicles from the axon back to the cell body. 78