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BIOL 1500
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Biology Chapter 3 Notes: Cells Cells • all organisms made of cells; most basic unit of life • first used in mid-1600s by Robert Hooke (British scientist); small rooms • Cell theory: all living organisms are made up of one or more cells; cells arise from other, pre-existing cells Prokaryotic Cells • Does not have a nucleus; DNA simply resides in the middle of the cell • Four basic structures: plasma membrane encompasses the cell (intracellular substances are within the cell); cytoplasm's jelly-like substance fills the cell; ribosomes makes proteins; one or more circular loops or linear strands of DNA • may have cell walls to protect and give shape to the cell • pili: Hair-like projections that help cells attach to other surfaces • Flagellum: whip-like projection(s) that aids in cellular movement • diverse metabolically Endosymbiosis Theory • a prokaryote entered a larger host prokaryote, eventually their existence became dependant on each other • Support: chloroplasts and mitochondria are similar in size to prokaryotic cells; have small amounts of circular DNA simular to prokaryotes; divide by fission like prokaryotes; have internal structures called ribosomes that are similar to bacteria ones Invagination • plasma membrane folds in on itself; other compartments are formed when new membrane encloses on the folded ones Eukaryotic Cells • about 1.5 billion years after prokaryotes • Typical features: DNA contained in nucleus; internal structures into compartments; larger usually by 10 times; cytoplasm has organelles Plasma Membrane • phospholipid bilayer (phospholipids) membrane that holds the contents of a cell in place and regulates what enters and exits the cell • Heads of the phospholipids re hydrophilic (polar) and the tails are hydrophobic (non- polar); a sheet is created • various protein, carb and lipid molecules are also attached to the bilayer • Transmembrane proteins: penetrate right through the lipid bilayer; surface proteins reside on the inner or outer surface of the membrane; lipids are within the hydrophobic tails • Receptor proteins: bind to chemicals in the cell's external environment; regulate certain processes within the cell; heart cell receptors bind to adrenaline in times of stress or fright • Recognition Proteins: a fingerprint that makes it possible for the body's immune system to distinguish the cells that belong inside your body from those that are invaders and need to be attacked; help cells bind to or adhere to other cells/molecules • Transport proteins: transmembrane proteins that help large/strongly charged molecules pass through the plasma membrane • Enzymatic proteins (enzymes): accelerate chemical reactions on the plasma membrane's surface • Short Branched Carbohydrate Chains: allows cell to be recognized by other cells like immune sys • Cholesterol: helps membrane maintain its flexibility • Fluid mosaic: plasma membrane comprised of many parts that aren't anchored in place • Faulty membranes: cystic fibrosis (chloride ions are restricted and hard to get mucus out of lungs) • Beta-blockers: treats anxiety • Have a fingerprint that identifies cells ("I belong here") Movement of molecules across membranes • Passive transport: molecular movement occurs spontaneously without input of energy; diffusion and osmosis • Diffusion: solute is dissolved in a gas or liquid (solvent) and moves from an area of high solute concentration to an area of a lower concentration; moves down their concentration gradient • Simple diffusion: gets through plasma membranes on their own (O2, CO2) • Facilitative diffusion: Most molecules may be repelled and electrically charged; they need a carrier molecule to pass/enter • Osmosis: passive diffusion of water across a membrane; water molecules will move to lower concentration areas; hypertonic solution contains more solutes in extracellular fluid (water diffuses out); hypotonic solutes contain lower concentrations are lower in extracellular fluid (water diffuses in); Isotonic (balanced); only determined by the total concentration of molecules • Active Transport: movement of very large molecules or molecules that move against their concentration gradient; uses up energy and ATP; digestion pushes H+ ions into stomach; when the transport uses energy directly from ATP to fuel, it is primary active transport; many transporter proteins use indirect method of fueling activities from ATP and it is called secondary active transport • Endocytosis and exoctytosis are used for bulk transport of particles: can be receptor mediated (LDL particles in cholesterol) • Phagocytosis: large particles are engulfed by cells / Pinocytosis: dissolves particles and liquids (amoebas, unicellular protists) Connections between cells • connections hold the cells in place and enable them to communicate with each other • Tight junctions: water-tight seals around cells and also anchor cells in place; important in the small intestine because it prevents excess water and bacteria to flow into your cells along with nutrients • Desmosomes: fasten cells together into strong sheets like a irregular interval of velcro (not water tight); lines tissue of animal body cavities, muscle tissue, holding fibers together; lack of this will form blisters • Gap junctions: pores surrounded by special proteins that form open channels between two cells; secret passageways for nutrients to flow through; cell-to-cell communication; important for the functioning of hearts; allows cells to recognize when they bump against other cells (contact inhibition); cancer cells do not have contact inhibition • In plant c
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