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The Cellular Level of Organization. Honors Anatomy & Physiology. Cells . ~200 different types cells in body all arise from cell division each type has unique role in supporting homeostasis . Parts of a Cell. Plasma Membrane separates inside from outside
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The Cellular Level of Organization Honors Anatomy & Physiology
Cells • ~200 different types cells in body • all arise from cell division • each type has unique role in supporting homeostasis
Parts of a Cell • Plasma Membrane • separates inside from outside • selective barrier that helps establish & maintain appropriate environment for normal cell activities • key role in cell-to-cell communication
Plasma Membrane • fluid mosaic model • lipid bilayer makes up basic structural framework • 3 lipid molecules • Phospholipids (~75% of membrane) • Cholesterol (~20%) • Glycolipids (~5%)
Phospholipids • *amphipathic: have both polar & nonpolar parts • made of • phosphate head (polar) • two long fatty acid (f.a.) chains (nonpolar)
Cholesterol • weakly amphipathic
Membrane Proteins • Integral Proteins • most transmembrane • amphipathic • hydrophobic a.a. extend among f.a. tails
Membrane Proteins • Peripheral Proteins • not embedded in membrane • ass‘c loosely with polar heads or integral proteins • inner or outer surface
Glycoproteins • protein + carbohydrate group attached that protrudes in ECF (never inside cell) • glycocalyx: all carbs attached to proteins or lipids on exterior surface of plasma membrane
Functions of Membrane Proteins • 1. Ion Channels • selective pores or holes (think straws) thru which specific ions can flow in/out of cell
Functions of Membrane Proteins • 2. transporters • selectively move a polar substance or ion across membrane
Functions of Membrane Proteins • 3. receptors • integral proteins that serve as cell recognition sites • recognize specific type of molecule called a ligand
Functions of Membrane Proteins • 4. enzymes • some integral (or peripheral) proteins catalyze specific chemical rx on inside or outside of cell
Functions of Membrane Proteins • 5. linkers • integral (or peripheral) proteins that anchor proteins in plasma membrane of neighboring cells to each other
Functions of Membrane Proteins • 6. cell-identity markers • glycoproteins (or glycolipids) • enable cell to recognize other cells of same kind during tissue formation • or to recognize & respond to foreign cells • ex: ABO bld type
Membrane Fluidity • individual molecules not static in membrane • *fluidity greater when there are more dbl bonds in the f.a. tails of phospholipids • cholesterol makes membrane stronger but less fluid @ normal body temps
Cell Membranes are Selectively Permeable • lipid bilayer permeable to most nonpolar, uncharged small molecules • & impermeable to ions & most charged or polar molecules • # of ion channels alters the membrane permeability
Concentration Gradients • because membranes are selectively permeable, differences in concentrations of chemicals between inside/outside of cell can exist • differences in charge across membrane = electrical gradient called a membrane potential
Transport Across Membrane • all ions & molecules have KE & each will move down its concentration gradient passively • diffusion • osmosis • active transport: material moves against its concentration gradient so cell must spend nrg • pumps • endo- & exo- cytosis
Passive Transport is diffusion of substance across membrane w/no nrg investment
Diffusion • higher concentration lower concentration • equilbrium reached when concentration same • movement continues
Rate of Diffusion Across a Membrane • affected by: • steepness of concentration gradient • temperature • mass of diffusing substance • surface area available for diffusing • distance material is diffusing thru
Materials That Diffuse Thru Plasma Membrane • nonpolar, hydrophobic molecules, fat-soluble vitamins, small alcohols, ammonia, small amts water and urea • gases: O2, CO2, N2, • steroids, • vit. A, D, E, K
Diffusion of Ions Across Plasma Membrane • ion channels: allow K+, Na+, Cl-, & Ca++ to move down concentration gradients when open
Osmosis • diffusion of water across semi-permeable (selectively permeable) membrane • water moves not the solute • Isotonic solution: • cell has same concentration of solutes as solution • Hypotonic solution: • cell has higher concentration of solutes than solution • Hypertonic solution: • cell has lower concentration of solutes than solution
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Facilitated Diffusion • solute moves passively by diffusion but requires a protein channel to cross membrane • *glucose binds to a specific transporter protein changes shape glucose crosses membrane thru transporter protein returns to its original shape
Facilitated Diffusion • http://programs.northlandcollege.edu/biology/Biology1111/animations/passive3.swf
Active Transport • used to move materials from high concentration side of membrane lower concentration side • ex: some ions, a.a., monosaccharides
Energy for Active Transport • 2 sources: • ATP • pumps • Na+/K+ pump • nrg stored in Na+ or H+ concentration gradient • 1 substance moves in down its concentration gradient & brings along 2nd material
Na+/K+/ATPase Pump • #1 pump in body cells
Na+/K+/ATPase Pump • http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/ion_pump/ionpump.html
Digitalis • medication given to patients with heart failure (weakened pumping action of heart) • action: • slows action of the Na+/K+ pumps which lets more Na+ accumulate inside cardiac muscle fibers decreased Na+ concentration gradient across plasma membrane Na+/Ca++ antiporters in these cells to slow down increases intracellular concentrations of Ca++ increases force of contractions
Secondary (2°) Active Transport • uses both symporters & antiporters that are powered by an ion concentration gradient (usually Na+ or H+)
Bulk Transport Across the Membrane used by large macromolecules or large volumes of smaller molecules Exocytosis Endocytosis
Phagocytosis • cell eats solid particles • neutrophils & macrophages are phagocytes
Pinocytosis • bulk-phase endocytosis • cell takes in ECF