Cell Bio Exam 4 sg.txt

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Cell Bio Exam 4 sg.txt
2010-12-08 19:04:57

BIO 353 Exam 4
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  1. What are the general characteristics of actin filaments?
    • * Helical polymers of actin protein, two protofilaments
    • * Seven nanometers in diameter
    • * Structurally polar, (+ and � end)
    • * Thinner, shorter and more flexible than microtubules
    • * Basic subunit is globular actin (G-actin)
    • * In most cases fast reactions to stimuli
    • * Located through cell in many arrangements most highly concentrated in the cells cortex
    • * Actin filaments found primarily in linear bundles, 2-D (sheets, bundles) and 3-D (gels)
  2. What are the mechanisms of polymerization and depolymerization?
    • * Similar strategy as microtubules
    • * Nucleotide (ATP) exchange/hydrolysis cycle
    • * ATP cap
    • * Microfilament organizing centers small, distributed, modular
  3. How do actin filaments modify behavior?
    There are 100s of proteins that bind actin and affect its nucleation, polymerization, and interactions with cellular components (including itself). They influence nucleation via Arps that nucleate actin filament growth from the minus end. Influence bundling. F-actin is organized into different assemblies based on type of cross-linking proteins. Non-contractile bundles and sheets. Actin Molecular motors.
  4. Contractile bundles?
    F-actin arranged in tight bundles of opposite polarities. Associated with Myosin II Example: stress fiber, contractile ring.
  5. What is the function of contractile bundles?
    Contractions, motility, adhesion to surfaces, cytokinesis.
  6. Non-contractile bundles and sheets?
    F-actin arranged in tight bundles and thin sheets, bundles, and are structurally polar. Example: filopodia, microvilli, lamellipodia. Associated proteins are Arp 2/3 and villin.
  7. Function of non-contractile bundles and sheets?
    Formation of non-contractile outgrowths at cell surface. Dynamic and ephemeral in mobile cells (wound healing, probing environment, growth cones), stable in cells requiring increased surface area.
  8. Gel-like network?
    F-actin arranged in a loose yet highly viscous 3D openarray with many interconnections, mixed polarity. Example: cell cortex.
  9. What is the function of the gel-like network?
    Forming dense bed of F-actin in cell cortex, support of plasma membrane and cytoplasm.
  10. Actin molecular motors?
    Myosin responsible for a variety of cellular movement; large family of proteins; nonprocessive. Myosin I: member of the myosin super-family involved in a number of cellular functions.
  11. Function of Actin molecular motors?
    Membrane trafficking, cell motility, cytokinesis, organelle transport.
  12. Myosin II?
    Conventional myosin, skeletal muscle, smooth muscle, and nonmuscle. Crucial for the movement of opposite orientes F-actin. Generates tension in stress fibers, contractile ring, adhesion belts, and muscle contractions.
  13. How are cells connected?
    Cells cling to each other either through 1) direct cell-cell interactions or 2) they may be bound together by the extracellular materials that they secrete.
  14. What is adhesion?
    The ability of cells to cling or stick to their surroundings. Cell adhesion if a fundamental principle of cell biology. The mechanism of adhesion govern the arrangement of different cell types in the body and influence cells behavior. The mechanism determines the architecture of the body (shape, strength, and arrangement of cells into tissues).
  15. Junctions betweens cells due to cell adhesion?
    They create pathways for communication, allowing the cells to exchange the signals that coordinate their behavior and regulate their patterns of gene expression. The making and breaking of the attachments and the modeling of the matrix govern the way the cells move within the organism (when the body grows, develops, and repairs itself).
  16. What do defects in cell adhesion underlie?
    A variety of diseases including cancer, thrombosis, inflammation.
  17. What are the 2 building strategies that multicellular structures use?
    These strategies correspond to 2 ways in which mechanical stresses can be transmitted across a multicellular structure 1) one strategy depends on the strength of the extracellular matrix. 2) the second strategy depends on the strength of the cytoskeletal filaments inside the cell and on cell-cell adhesion which tie the cytoskeleton and to the underlying matrix.
  18. How do mechanical stresses transmit through epithelial tissue?
    They are transmitted from cell to cell by cytoskeletal filaments anchored to cell-matrix and cell-cell adhesion sites.
  19. How do mechanical stresses transmit through connective tissue?
    Extracellular matrix directly bears mechanical stresses of tension and compression.
  20. Connective tissue?
    In bone or tendon. The extracellular matrix id plentiful, and the cells are sparsely distributed within it. The matrix is rich in fibrous polymers, especially collagen. In these tissues, it is the matrix, rather than the cells, that bears most of the mechanical stress to which the tissue is subjected. Direct attachments are relatively rare, but the cells have important attachments to the matrix allowing them to pull on it and to be pulled on by it.
  21. Epithelial tissue?
    Cells are closely bound together into sheets called epithelia. The extracellular matrix is scanty, consisting mainly of a thin mat called the basal lamina which underlies one face of the sheet. The cells are attached to each other directly by cell-cell adhesions, where cytoskeletal filaments are anchored, transmitting stressors across the interior of each cell, from one adhesion site to another adhesion site.
  22. The extracellular matrix?
    Complex network of proteins and polysaccharide chains that the cell secrete and deposit around themselves as an insoluble material.
  23. The basal lamina?
    One defining feature common to all multicelluar organisms. It is an essential underpinning (mechanical support) of all epithelial. It is a very thin, tough, flexible sheet of matrix molecules which underlies all types of epithelial. Separates epithelial, fat, muscle and Schwann cells from underlying or surrounding connective tissues.
  24. Functions of the basal lamina?
    Structural support, filtering (in kidney), determines cell polarity, promotes cell survival.
  25. Components of the basal lamina?
    Laminin, type IV collagen, nidogen, perlecan.
  26. Examples of fibrous proteins (glycoproteins)?
    Laminin, type IV collagen, nidogen, fibronectin.
  27. Examples of proteoglycans?
    Perlecan, hyaluronan, decorin, aggrecan.
  28. What is laminin?
    Laminin is the primary organizer of the sheet structure of the basal lamina. The 3 chains of the lamina molecule are disulfide-bonded into a cross-like structure. These molecules can self-assemble in vitro into a network, largely through the interactions between their heads.
  29. What is type IV collegen?
    A second essential component of the basal lamina that gives tensile strength. The collagen molecules have globular domains that interact with each other to assemble extracellularly into a flexible, felt-like network.
  30. What is a fibroblast?
    The predominant cell type in tissues which secretes abundant extracellular matrix.
  31. Extracellular matrix influences?
    Cell survival, cell division (proliferation), cell migration, cell shape, cell function.
  32. What forms cartilage?
  33. What forms bone?
  34. What are the polysaccharides in proteoglycans?
  35. What are glycosaminoglycans GAGs?
    They are polysaccharides in the ECM. They are called GAGs because one of the two sugars in the repeating disaccharide is always an amino sugar which in most cases is sulfated. Because there are sulfate or carboxyl groups on most of their sugars, GAGs are highly negatively charged. They are the most anionic molecules produced by animal cells.
  36. What are the 4 main groups of GAGs?
    1) Hyaluronan, 2) chondroitan sulfate and dermatan sulfate 3) heparin sulfate, and 4) keratin sulfate.
  37. What is the main function of GAG? What are the other functions of GAG?
    To resist compression and serve as a space filler. Filters to regulate the passage of molecules through the extracellular space. GAGs bind growth factors and present them to cells. They guide cell migration through the matrix.
  38. What enables the matrix to withstand compressive forces?
    Swelling pressure
  39. What is the function of Hyaluronan?
    It acts as a space filler during embryonic development, facilitates cell migration in wound healing, helps in resisting compressive forces in tissues and joints.
  40. What is Hyaluronan?
    It is the simplest GAG and does not contain sulfated sugars. It is a common ingredient in skin care products
  41. Fibrous proteins of the ECM?
    Collagens, fibronectin, and elastin
  42. What are collagens?
    Collagens are the major proteins of the ECM and collagen I is the most common collagen of connective tissues. Collagen I is the principal molecule of bone and skin. After being secreted into the extracellular space, the collagen molecules assemble into high-order polymers called collagen fibrils which often aggregate into larger, cable-like bundles as collagen fibers.
  43. Collagen functions in connective tissues?
    In contrast to GAGs which resist compressive forces, collagen fibrils form structures that resist TENSILE forces. The fibrils have various diameters and are organized in different ways in different tissues.
  44. Elastin?
    Gives tissues their elasticity
  45. Fibronectin?
    Helps cells attach to the ECM and guides cell movements in developing tissues by serving as tracks along which cells can migrate. Fibronectin and integrin molecules attach a cell to the ECM.
  46. Integrins?
    Integrins couple the matrix outside a cell to the cytoskeleton inside it. An integrin molecule switches to an active conformation when it binds to molecules at either of its ends.
  47. What are junctions?
    Physical attachments between the cells or between the cells and the ECM.
  48. What are the 3 types of cell junctions?
    Anchoring junctions, occluding junctions, and channel-forming (GAP) junctions.
  49. What are anchoring junctions?
    Include both cell-cell and cell-ECM adhesions. These junctions are linked with the cytoskeleton and transmit diseases.
  50. What are occluding junctions?
    They seal the gaps between cells in the epithelia. They make the epithelial sheet impermeable to outside molecules. Even water soluble molecules cannot easily leak between the cells. AKA tight junctions. They also function as �fences� to help separate domains within the plasma membrane of each cell, so they hinder apical proteins from diffusing into the basal region, and vice versa. Thus, they play a key role in maintaining the polarity of individual epithelial cells. (they prevent lateral movement)
  51. What forms tight junctions?
    Claudins and occludins that are arranged in strands along the lines of junction to create a seal. The extracellular domains of these proteins adhere directly to one another to occlude the intercellular space.
  52. What are channel-forming (GAP) junctions?
    They create passageways that link the cytoplasm of adjacent cells. They allow the passage of small molecules and ion from cell to cell. GAP junctions create an electrical and metabolic coupling between the cells. They allow action potentials to spread rapidly from cell to cell and they allow neighboring cells to share signaling information. This creates an electrical and metabolic coupling between the cells.
  53. Connexons?
    Are made from an assembly of 6 connexins (called a hemichannel) which assemble to form a connexon and penetrate the opposed lipid bilayers. Two connexons join across the intercellular gap to form a continuous aqueous channel connecting the two cells.
  54. What are the actin filament attachment sites?
    1) Cell-cell junctions (adherens junction) 2) cell-matrix junctions (actin-linked cell-matrix adhesions)
  55. What are intermediate filament attachment sites?
    1) cell-cell junctions (desmosomes) 2) cell-matrix junctions (hemidesmosomes)
  56. Transmembrane adhesion proteins?
    Span the membrane and anchor the cytoskeletal filaments. They have 2 superfamilies based on the 2 basic kinds of attachment: cadherin (cell-cell attachment) and integrin (cell-matrix attachment)
  57. Cadherins?
    Depend on Ca2+ ions. Removing Ca2+ from extracellular medium causes adhesion mediated by cadherins to come adrift. Without Ca2+, cells will disassociate. Only found in multicellular organisms.
  58. Cadherins in development?
    Cells in an early embryo only stick together weakly because there is no adherins. Cadherins begin to be expressed at about the 8-cell stage and the cells become strongly and closely attached. This process is called compaction.
  59. Homophilic?
    Means that cadherin molecules of a specific subtype on one cell bind to cadherin molecules of the same sub-type on adjacent cell. This interaction occurs at the n-terminal tips of the cadherin molecules. The protein here forms a terminal knob and nearby pocket. The cadherin molecules protruding from opposite cell membranes bind by insertion of the knob of each one in the pocket of the other.
  60. Accessory anchor proteins?
    Mediate the indirect linkage of cadherins to the cytoskeleton. They assemble on the tail of the cadherin.
  61. Adhesion belt?
    Continuous adherin junctions in epithelia close beneath the apical face of the epithelial layer encircling each of the interacting cells in the epithelial sheet. In embryology, the belts contractibility helps in morphology.
  62. Adherens junctions?
    Are an essential part of the machinery for modeling shapes of multicellular structures in animal morphogenesis. Contractibility can induce invagination of epithelial sheets.
  63. Desmosome?
    Junctions similar to adherens junctions, but instead of linking to actin, they link to intermediate filaments. Very plentiful in the epidermis.
  64. What is the main function of desmosomes?
    To provide mechanical strength.
  65. Hemidesmosomes?
    Hemidesmosomes are spot-weld epithelial cells to the basal lamina linking the ECM protein laminin outside the cell to keratin intermediate filaments inside it. The linkage is mediated by integrin proteins.
  66. What is the process of cell duplication?
    The cell cycle
  67. What composes the cell cycle?
    Interphase and M phase
  68. Interphase?
    The longest phase (~90%) where the cell appears deceptively inactive. Consists of the G1 phase, G0 phase, S phase, G2 phase.
  69. G1 phase?
    The 1st �gap� stage after M phase. Cell growth, gene transcription, protein synthesis, DNA repair, Monitoring/responding to external, and organelle division all occur.
  70. G0 phase?
    Extending �resting� state; cell�s entry into S phase is delayed for days, weeks, or years. Many cells remain permanently in G0 (nerve cells, skeletal muscle cells, mature tissues)
  71. S phase?
    DNA synthesis stage when replication of DNA (no separation yet) and replication of centrisomes (no separation yet) occur.
  72. G2 phase?
    The 2nd gap stage when growth continues as in G1 and final preparations to enter M phase
  73. M phase?
    Shortest and most dynamic phase when the process of cell division, divided into mitosis (nuclear division) and cytokinesis (cytoplasmic division).
  74. Mitosis?
    Division of a cell into 2 daughter nuclei with 5 overlapping subphases: prophase, prometaphase, metaphase, anaphase, and telophase.
  75. Cytokinesis?
    The cytoplasm is divided into two.
  76. Prophase?
    1) Replicated chromosomes condense, which is aided by DNA binding protein condensin. 2) Sister chromatids are held together by cohesin. 3) Mitotic spindle starts to assemble. 4) Centrosomes separate. 5) Kinetichores form on centromere region.
  77. What protein holds sister chromatids together?
  78. What protein aids in condensing DNA?
  79. Condensin?
    Forms ring like structures and help to coil the mitotic chromatids into smaller, more compact structures that can be more easily segregated during mitosis.
  80. Cohesins?
    From protein rings that surround the sister chromatids keeping them united. This is crucial for proper chromosome segregation, and is broken completely only in late mitosis to allow the sister chromatids to be pulled apart by the mitotic spindle.
  81. Mitotic spindle assembly?
    Dependant on microtubules.
  82. Centrosomes separate?
    Centrosomes separate during prophase. They are the principle microtubule organizing center. Centrosome duplication begins at the start of S phase. It duplicates so that it can help form the 2 poles of the mitotic spindle and so each daughter cell can receive its own centrosome.
  83. Kinetochores?
    Kinetochores assemble on the condensed chromosomes during late prophase. They attach chromosomes to the mitotic spindle.
  84. Prometaphase?
    Abrupt breakdown of the nuclear envelope allowing the chromosomes to attach to spindle microtubules via their kinetochores. The breakdown is facilitated by disassembly of lamina.
  85. Metaphase?
    Paired kinetochore microtubules on each chromosome attach to opposite poles of the spindle. There are 3 populations of spindle microtubules that make up the mitotic spindle: the kinetochore, interpolar, astral. Chromosomes are aligned at the equator of the spindle, midway between the spindle poles forming the metaphase plate.
  86. Anaphase?
    Sister chromatids synchronously separate, and each is pulled slowly toward the spindle pole it is attached to. Kinetochore microtubules get shorter, and the spindle poles also move apart, both contributing to chromosome segregation.
  87. Anaphase promoting complex (APC)?
    Triggers the separation of sister chromatids by promoting the destruction of cohesions. The activated APC indirectly triggers the cleavage of the cohesions that hold sister chromatids together. It catalyzes the ubiquitylation and destruction of inhibitory protein called securing. When freed from securing, separase cleaves the cohesion complexes, allowing the mitotic spindle to pull the sister chromatids apart.
  88. Securin?
    Inhibits the activity of proteolytic enzyme called separase.
  89. Types of movement during anaphase?
    Anaphase A and anaphase B.
  90. Anaphase A?
    Movement during anaphase where chromosomes move towards poles by depolymerization of kinetochore microtubules and action of motors.
  91. Anaphase b?
    Movement during anaphase where poles move apart by elongation of interpolar microtubules and action of motors on interpolar and astral microtubules.
  92. Telophase?
    1) Kinetochore microtubules depolymerize. 2) Interpolar microtubules elongate further and continue to push spindle poles apart. 3) nuclear envelope reforms 4) condensed chromatin expands 5) contractile ring forms, identifying the plane of division.
  93. M phase?
    1) Cytoplasm is divided in two by a contractile ring, which pinches in the cell to create two daughters, each with one nucleus. 2) Tightening of contractile ring belt produced cleavage furrow. This belt is a bundle of actin microfilaments, myosin II and other associated proteins. 3) Reformation of the interphase cytoplasmic microtubules. 4) M phase ends, cell enters G1 phase.
  94. Cell cycle check points?
    Ensure that key processes in the cycle occur in the proper sequence. The checkpoint determines whether or not the cell proceeds to the next phase of the cycle. This determination is based on external and internal conditions and factors.
  95. Cell cycle control systems?
    Govern the cell cyles by cyclicaly activating and then inactivating key proteins and protein complexes. The 2 key families of proteins that control the cell cycle are cyclins and cyclin-dependent protein kinases (Cdks).
  96. Cyclins?
    Regulatory subunits of the cyclin-dependent protein kinases.
  97. Cyclin-dependent protein kinases (Cdks)
    Cyclin-dependent protein kinases are kinases involves in the initiating and sustaining events of the cell cycle. Cdks are inactive unless bound to cyclins.
  98. What regulates the activity of Cdks?
    The accumulation of cyclins. Cyclin levels in the cell rise and fall with the stages of the cell cycle (while Cdk levels remain stable). Increased cyclin concentration results in increased binding and activity of specific Cdk. So, Cdk activity is low in interphase, but increases in mitosis.
  99. Active cyclin-cdk complexes?
    G1-Cdk. G1/S-Cdk. S-Cdk. M-Cdk.
  100. Cdk activation?
    For Cdk to be active, it must first be bound to cyclin, then phosphorylated at one site and dephosphorylated at 2 other sites.
  101. Cyclin/Cdk function of G1/Cdk?
    Increased cyclin levels occur early to mid G1, binding to specific Cdk forms active complex G1-Cdk which helps drive cell through G1 toward S phase. This activation is induced by extracellular signals (growth factors, hormones) and oncogenes (Ras)
  102. G1/S-Cdk or S-Cdk?
    Increased cyclin levels occur late in G1, binding to distinct Cdk proteins to form S-Cdk or G1/S-Cdk which trigger entry into S phase. S-Cdk activates origins of replication leading to DNA replication and makes sure the DNA replication only occurs one per cell cycle.
  103. DNA damage checkpoints?
    Help prevent the replication of damaged DNA. When DNA is damaged, specific protein kinases respond by activating p53 protein and halting its normal rapid degredation. The activated p53 then accumulates and binds to DNA. There it stimulates the transcription of the gene that encodes for Cdk inhibitor protein p21. P21 inactivates G1/S-Cdk and S-Cdk and arrests the cell cycle in G1 which gives time for cell to repair DNA. If DNA is beyond repair, the cell will undergo apoptosis.
  104. M-Cdk?
    Increased cyclin levels drive cell to M-phase, binding to mitotic cyclin dependent kinase vreates the active complex called M-Cdk. For M-Cdk to be active, it must be phosphorylated at 1 site and dephosphorylated at 2 other sites.
  105. Activation of M-Cdk?
    When M-cyclin-Cdk is first formed it is inactive. Cdk id phosphorylated at one site by enzyme called Cdk-activating kinase (Cak). Cdk is phosphorylated at 2 other sites that inhibit its activity by an enxyme called Wee1. Sctivation of M-Cdk is triggered b the removal of the inhibitory phosphates by the Cdk-activating phosphatase (Cdc25). Activation of M-Cdk indirectly activates more M-Cdk, creating a positive feedback loop. The overall consequence of this explosive increase in M-Cdk is that it will drive the cell abruptly from G2 to M phase.
  106. What regulated the abundance of cyclins?
    Protein degredation. The cyclin becomes covalently modified by addition of multiple copies of ubiquitin at the end of mitosis. Ubiquitination is mediated by the anaphase promoting complex (APC). Ubiquitination marks cyclins for destruction by large proteolytic machines called proteosomes.
  107. Characteristics of apoptosis?
    1) Cell shrinks and chromatin condenses. 2) Cytoskeleton collapses. 3) Nuclear envelope and other organelle membranes disassemble. 4) DNA breaks up into fragments. 5) Alteration in cell surface and cell fragmenting. 6) Phagocytic cells clean up before cell lysis thereby avoiding cell necrosis.
  108. Where do apoptotic pathways usually target?
    Mitochondria. Activation of the apoptotic program is highly regulated and triggered in an all or nothing fashion.