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BIOL 130 Study Notes Unit X Social Networking of Cells

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BIOL 130
Richard Ennis

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Unit 10/11 Cells in their Social Context  The Cytoskeleton: • A network of fibres forming the shape of the cell within the cytoplasm • It determines the shape of the cell and the position of the organelles • Allows the organelles to also be moved around in the cell o By extension, also allows movement of chromosomes during mitosis • Aids the cell’s own movement (motility) o Formation of flagella, cilia, etc. • Unlike our skeleton, the cytoskeleton is dynamic (i.e. constantly being reorganized Classes of Microfilaments: • There many different types of proteins depending on the intermediate filament o Even intermediate filaments in different cells of the same organism can have different proteins • In the nucleus: o Nuclear lamins – in all animal cells • In the cytoplasm: o Neurofilaments – In nerve cells o Vimentin & Vimentin-related – in connective tissue, muscle cells, and neuroglial cells o Keratins – in epithelia Keratins: Most Diverse Intermediate Filaments • The most diverse class of intermediate filaments o Every type of epithelium in the body has its mixture of keratin protein o Gut lining, skin, tongue, etc. • Skin produces many types of keratin o Filaments can form fingernails, hair, toenails, hooves, rhino horns, etc. • Keratinized layers of skin can server as a semi-waterproof barrier for skin o The topmost layer of the epidermis (skin) is constantly shedding cells o These cells are dead and flattened and packed with keratin to form a barrier. o The under-layers, including the dermis (connective tissue) is constantly producing cells via division as old cells are being shed Microtubules: Hollow Tubes of Tubulin • The subunit of microtubules is the tubulin heterodimer • Microtubules have a plus end and a minus end o The tubulin heterodimers polymerize spontaneously to the “plus end” and go downwards to create protofilaments o All of them have the same orientation and therefore a definite structural polarity • Protofilaments come together and collectively form tubes  microtubules • Roles of microtubules: o They are stable and capable off forming structures such as: cilia, flagella, etc. on certain cells o They can be dynamic and play an important role in organizing eukaryotic cells:  Cell shape, positioning of organelles  Movement of chromosomes during mitosis (i.e. spindle microtubules)  Form system of tracks for movement of vesicles and organelles • Biological motor able move along a suitable surface o Powered by ATP hydrolysis • Kinesins – motors that move toward the plus end of the microtubule (axon terminal) • Dyneins – motors move toward the minus end (cell body) Microfilaments (Actin Filaments): • Actin filaments allow eukaryotic cells to adopt a variety of shapes and perform a variety of functions o A) microvilli; o B) Contractile bundles in cytoplasm; o C) Filopodia; o D) Contractile ring during cell division • Actin filaments and cell movement: o Actin polymerization at the leading edge of the cell pushes the plasma membrane forward (Protrusion) o This forms new regions of actin cortex, where new points of anchorage are made between the actin filaments and the surface that the cell is on (attachment) o Contraction at the rear of the cell draws the body of the cell forward (traction) o New anchorage points are established at the front and old ones are released at the back  Causes the cell to be able to crawl forward Extracellular Matrix & the Cell Wall – Common Features: • Cross-linked network of filaments o Resists stretching and straining forces • Semi-solid gelatinous matrix (polysaccharides and proteins) o Resists compression Model System for Epithelium and Extracellular Matrix: • Cells supported internally by the cytoskeleton • Held together by cell-to-cell junctions and the extracellular matrix (ECM) o ECM is secreted by the cells themselves • Animal cells need to be strong, yet capable of rapid movement, and quick changes to shape Connective Tissue: • Best characterized by large amounts of extra cellular matrix o The ECM provides mechanical support • Other types of connective tissue: o Bone, cartilage o Tendons, dermis of the skin o Adipose (fat) o Aqueous humor of eye • By contrast though, o The epithelium, muscle, and neural tissues are all examples where the cel
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