CHAPTER 7 BIOLOGY NOTES Definitions relevant to substance movement The concentration of molecules is the number of them in a given volume unit A gradient is a physical difference in temperature pressure charge or concentration in two adjacent regions A fluid is a substance that can move or change shape in response to external forces A solute is a substance that can be dissolved dispersed as ions or molecules in a solvent A solvent is a fluid capable of dissolving a solute Plasma Membrane surroundings Boundary that separates the living cell from its Is dynamic and ever changing structure Exhibits selective permeability What is the composition of the membrane Phospholipids Proteins Cholesterol Fluid mosaic model 1970 s Fluid lipids Mosaic proteins Determine most of membranes specific functions Integral a b Peripheral Phospholipids Amphipathic Most abundant lipids Spontaneously form bilayers in aqueous environments Lipids are laterally mobile within the membrane o Lateral movement 10x a second o Flip flop once a month Fluidity of membranes is affected by the degree of saturation of the fatty acid tails of the phospholipids unsaturated hydrocarbon tails gives fluidity saturated hydrocarbon tails creates viscosity Cholesterol o is amphipathic membrane in animal cells o acts as buffer against temperature changes in animal membranes o high temperatures restrains phospholipid movements and holds them together o low temperatures doesn t allow packing of phospholipids integral membrane proteins are embedded in the lipid bilayer peripheral proteins are loosely associated with the lipid bilayer or with integral proteins o most integral membrane proteins are transmembrane proteins span the membrane use alpha helices integral membrane proteins o transport o enzymatic activity o signal transduction o cell cell recognition o intercellular joining o attachment to the cytoskeleton and extracellular matrix cell must exchange materials with its surroundings process controlled by plasma membrane o plasma membrane is selectively permeable regulating the cells molecular traffic high permeability gasses very small uncharged polar molecules moderate permeability water urea low permeability polar organic molecules glucose very low permeability ions charged polar molecules and macromolecules amino acids ATP proteins polysaccharides nucleic acids DNA RNA diffusion molecules diffuse down their concentration gradient to reach a uniform distribution at equilibrium osmosis diffusion of water across a membrane passive transport down the concentration gradient across a selectively permeable membrane tonicity ability of a solution to cause a cell to gain or lose water o hypotonic solution lysed animals turgid plants solute concentration lower outside of the cell than inside o hypertonic shriveled animals plasmolyzed plants the solute concentration higher outside of the cell than inside o isotonic normal animals flaccid plants solute concentration equal on both sides simple diffusion passive transport tendency for molecules to spread out evenly into the available space o down concentration gradient o usually small hydrophobic CO2 02 hydrocarbons facilitated diffusion passive transport transport proteins speed the passive movement of molecules across the plasma membrane o used for hydrophilic molecules polar ions etc o carrier proteins bind to molecules and change shape to shuttle them across the o channel proteins allow passage of hydrophilic substances across the membrane membrane Ex aquaporins Aquaporins 3 bill water molecules sec specific for water allow fast diffusion through cell membrane 1st reported 1992 Discovery awarded 2003 nobel prize in chemistry Osmoregulation control of water balance is a necessary adaptation for life in such environments o Paramecium o Fresh water vs saltwater fish Contractile vacuole fills with fluid that enters from a system of canals radiating throughout the cytoplasm when full the vacuole and canals contract expelling fluid from the cell Active transport requires ATP o Moves substances against their concentration gradient o Requires energy usually in the form of ATP o Is performed by specific proteins embedded in the membranes Electrochemical gradient drive the diffusion of ions across a membrane o Chemical force ions concentration gradient and an electrical force effect of the membrane potential on the ions movement 25 of all ATP drives sodium and potassium ions in and out of the cell Major electrogenic pump of animal cells transport protein that generates voltage across a membrane Bacteria plants and fungi use proton pump electrogenic pump to create a voltage differential across the plasma membrane Cotransport active transport that uses the energy from a favorable gradient to drive transport against an unfavorable gradient Bulk transport large package transport o Packaging vesicles required o Requires ATP o Used for large molecules proteins polysaccharides o Exocytosis expelling molecules o Endocytosis taking in molecules Phagocytosis takeup solids Pinocytosis takeup liquids Receptor mediated endocytosis
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