Movement across membranes

  • membranes are made of phospholipids, glycoproteins, cholesterol and intracellular/extra cellular proteins
  • Fluid mosaic model :: fluid phospholipids which can move with proteins embedded
  • Function of intrinsic proteins:: structural support, movement of water soluble molecules, ion channels for active transport
  • Functions of extrinsic proteins:: receptors, cell recognition, cell adherence
  • Factors affecting permeability:: temperature, organic solvents, pH
  • Higher temperature :: more energy an increased fluidity/permeability
  • Too high temperature :: proteins denature affecting permeability, eventual breakdown
  • Organic solvents :: dissolve the membrane, increasing fluidity
  • Diffusion:: passive movement of small, non-polar, lipid-soluble molecules from an area of high concentration to an ease of low concentration down a concentration gradient
  • Factors affecting rate of diffusion:: temperature, diffusion distance, steepness of concentration gradient, side of molecule, surface area
  • Osmosis:: passive movement of water molecules form an area of high water potential to an area of low water potential through a semi-permeable membrane
  • Water potential :: tendency of water molecules to move from one area to another
  • Incipient plasmolysis :: result of placing cells in an isotonic solution, cell membrane pulls away from cell wall in some areas
  • Facilitated diffusion :: the passive net movement of substances down a concentration gradient through transport proteins
  • Active transport :: the net movement of substances from an area of low to high concentration against a concentration gradient through carrier proteins using energy in the from of ATP
  • Endocytosis :: bulk uptake of substances into a cell by invagination of the membrane to form a vesicle (active)
  • Phagocytosis :: uptake of solids
  • Pinocytosis :: uptake of liquids
  • Exocytosis :: bulk transport of substances out of a cell, vesicle fuses to plasma membrane (active)
  • Isotonic:: solute potential is equal on each side of the membrane (equilibrium)
  • Hypertonic:: water potential is lower outside the cytoplasm, net movement of water is out of the cell
  • Hypotonic:: water potential is lower inside the cytoplasm, net movement of water is in to the cell