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The Cell The stuff that has been boring you for years! (Brought to you by the people who make learning mandatory so that we can keep our jobs and have summer off!) Cytoskeleton Structural support for motility and regulation Allows cell to change shape mechanically transmits signals from surface to interior constructed from three types of fibers microtubules (thick) microfilaments(thin) Intermediate fibers Microtubules Found in Eukaryotic Cells, hollow, straight, constructed of globular protein called tubulin, reinforce cell shape Tracks for organelle movement by motor molecules Separate chromosomes during cell division Centrosomes, centrioles, cilia, flagella Centrosomes and Centrioles Centriole: pair of cylindrical structures located in centrososme, composes of nine sets of triplet microtubules arranged in a ring, replicate during division Cilia and Flagella May propel, or draw fluid across membrane extension of plasma membrane with core of microtubules, 9 + 2 pattern, identical to centrioles, anchored by basal body Use ATP to power dynein movement Microfilaments Solid rods of globular protein (actin) wound into helix Provide cellular support, bear tension, aide in muscle contraction (myosin), cytoplasmic streaming, and localized contraction for the cleavage furrow during cell division Intermediate filaments Composed of Keratin, more permanent the microtubules and microfilaments Bear tension, framework for cytoskeleton, fix organelle position (nucleus) Membrane Structure Plasma membrane is boundary btwn living and nonliving, 8nm thick, controls chemical traffic, selectively permeable Made of amphipathic phospholipids, means hydrophilic and hyrdrophobic region present Fluid Mosaic Membrane Membrane held together by weak hydrophobic interactions lipids and proteins drift w/in membrane must be fluid to work properly, moderated by cholesterol membrane less fluid at warmer T by restraining movement of phospholipids at low T, prevent packing of phoshpolipids Membrane is a mosiac of diff proteins embedded an dispersed in a phoshp. Bilayer Integral proteins: transmembrane, peripheral proteins: attached to mem.surface, Distinct directional orientation Carbs on exterior, proteins also have directional orientation Cell-Cell Recognition Basis for: sorting of embryo’s cells into tissues and organs rejection of foreign cells by immune system Recognize by carbs branched oligosaccharides bonded covalently to lipids and proteins Cell Communication Communicating cells may be close or far apart, communicate by local regulators or hormones Three stages of cell signaling : Reception Transduction Response Signal Reception Chemical signals bind to specific receptors (receptor protein) Signal molecules complement to specific region or receptor protein signal behaves as ligand (small molecule to large molecule) Signal receptors are plasma mem. proteins Signal Transduction Pathways Pathways relay signals from receptors to cellular responses Chain of reactions Information is passed along, passes along info not molecule second messengers; Cyclic AMP, Ca ions Cellular Responses to Signals In response to signal, cell may regulate activity in cyto or transcription in nucleus Pathways amplify and specify responses cAMP: few to many target cells with receptor bind to specific signaling molecule Regulation of Cell Cycle Controlled by a clock Internal and external cues regulate Chemical-nutrients, growth factors Physical-density-dependent inhibition Cancer cells have escaped from cycle controls Cancer Do not stop due to density inhibition Make growth factors themselves, is abnormal signal Divide indefinitely as long as nutrients are available, normal 20-50 times Stop dividing at random points Immune system normally recognizes If avoid regulation, from tumor, unregulated mass of normal tissue Benign tumor: remain at this original site and can be completely removed Malignant tumor: invasive, impair normal function of organs, cancer Properties of Malignant tumors Anomalous cell cycle, Unusual chromosome # Lost attachment to neighboring cells, may cause separation from original tumor Migrating cells invade other parts of body, form more tumors Spread is call metastasis Metabolism and Energy of Life Metabolism: Totality of organism’s chemical processes Catabolic Paths: release E by breaking down Anabolic Paths: consume E to build complex from simple ATP Powers cellular work by coupling exergonic to endergonic rxns Ex: net loss of free energy En: E requiring that get net gain of E Drives mechanical, transport, and chemical work in cells works by transferring phosphate group Enzymes Speed up and control biochemical and metabolic rxns by lowering energy barriers Catalyst: accelerates rxn w/o being changed, so used over and over Enzymes: biological catalysts made of proteins Enzymes are Substrate Specific Depends on enzymes 3D shape Substrate: substance an enzyme acts on and makes more reactive Active Site: restricted region of an enzyme molecule which binds to substrate, changes its shape in response to substrate, called induced fit Active Site, catalytic center Hold two or more reactants in proper position for they may react Active site conducive to particular type of rxn the higher substrate [ ], the faster the reaction, up to a limit Cell’s Physical & Chemical env. Affects Enzyme activity T and pH effect rate Increasing T, increase rate until reach denature point of enzyme and cells optimal in humans: 35o to 40oC optimal pH is 6-8 some work best in extreme pH, like pepsin (digestive) at pH of 2 Cofactors: small nonprotein molecules required for catalysis Enzyme Inhibitors: some reversible (weak bonds), or irreversible (covalent) Competitive: resemble normal substrate, block active site, Noncompetitive: bond to other enzyme site, cause enzyme to change shape so active site cannot bond, metabolic poisons Control of Metabolism Metabolic pathways are regulate by controlling enzyme activity Allosteric regulation: Feedback inhibition Cooperativity: Location of enzymes orders metabolism Allosteric Regulation Uses site other than active site 2 Conformations: catalytically active, and inactive Binding stabilizes active conformation Makes it more or less reactive to substrate Feedback Inhibition Regulation of metabolic pathway by its end product, which inhibits an enzyme within the pathway Prevents cell from wasting chemical resources Cooperativity Substrate molecules may enhance enzyme activity substrate binding to active site induces substrate binding at other sub-unit active site