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REVISED Cell membrane powerpoint diffusion and osmosis revised

REVISED Cell membrane powerpoint diffusion and osmosis revised






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    REVISED Cell membrane powerpoint diffusion and osmosis revised REVISED Cell membrane powerpoint diffusion and osmosis revised Presentation Transcript

    • Cell Boundaries
      Chapter 6
    • What are boundaries?
      We have borders surrounding countries
      We have boundaries on a playing field
      Why are borders important?
    • What are the borders of a cell?
      Cell membrane
      Thin, flexible barrier
      Cell wall
      Plant, algae, fungi, prokaryotes
      Strong supporting layer
    • Cell Membrane
      What does it do for cell?
      Controls what goes in and out
      Regulates molecules moving from one liquid side of the cell to the other liquid side of the cell
    • Cell Membrane
      Lipid bilayer
      What are lipids?
      What does bi- mean?
      What’s a layer?
      A cell membrane is made of two
      layers of lipid molecules
    • Cell membrane
      Phospholipids bilayer
      Made of a negatively charged phosphate “head”
      Attracts water because the phosphate is charged (-)
      Water is a polar , slightly positive ends and slightly negative ends
      Attached to the phosphate group are 2 fatty acid chains
      Hydrophobic= don’t like water
      So the inside of the cell membrane doesn’t let water in but the outside allows cells to be dissolved in aqueous environments
    • Other things in the membrane…
      Proteins embedded in lipid bilayer
      Carbohydrates attached to proteins
      So many different molecules in membrane, we call it a “mosaic” of different molecules
    • Proteins
      Proteins help things get across membrane
      Kinda like a pump
    • Carbohydrates…
      Chemical identification cards
      “ID” card of cell
      Helps individual cells id each other
    • Cell Walls
      Outside cell membrane (does NOT replace membrane!!!)
      Plants, algae, fungi, prokaryotes
      Have pores to allow things in
      Function: SUPPORT and PROTECT
    • Cell walls made of…
      Protein and carbs
      Plant cell walls made up of CELLULOSE
      This is a tough carbohydrate
      Wood and paper
    • A biological membrane
      Cells exist in liquid environments
      Things need to get in and out of cell
      Different ways to do this….
      The Cell Membrane
    • Concentration (conc.)
      Mix of 2 or more substances
      Substance dissolved in solution
      Molarity (M) is # of Moles of a substance per liter of solution
      6.02 x 1023 “small things” (molecules, atoms, ions, electrons, ions, etc)
      Moles is a unit for measuring EXTREMELY small things
      is mass of SOLUTE in a given volume of solution (g/L)
      What is the concentration of 12 grams of salt dissolved in 3 liters of water?
      12g/3L= 4g/L
    • Diffusion
      Particles constantly move
      Collide randomly
      Spread out randomly
      Diffusion is moving from area of HIGH conc. to area of LOW conc.
      This is what we call the CONCENTRATION GRADIENT
    • Equilibrium
      When the conc. Of a system is the same throughout
      (same conc. on both sides)
    • What happens when we reach equilibrium?
      Particles continue moving across membrane but in both directions!***No more changes in concentration
    • If things can cross a membrane we call the membrane PERMEABLE
      If things canNOT cross a membrane we call the membrane IMPERMEABLE
    • Biological membranes are…
      Selectively permeable
      Cell membranes are picky
    • What’s this have to do with cells?
      Cell have liquid inside and are found in liquid environment
      We have substances (solutes) inside and outside cell
      Unequal concentrations means we get DIFFUSION!!!
      B/c diffusion depends on random particle movements, substances diffuse across membranes without requiring the cell to use energy
    • What diffuses across the membrane???
      Small, uncharged (non-polar) molecules
      Carbon dioxide
    • Cells are always trying to Maintain Equilibrium by…
      PASSIVE Transport
      Requires NO energy
      Goes with Conc. Gradient
      3 types:
      No protein required
      Small, uncharged particles
      CHANNEL or CARRIER proteins
      Trans-membrane protein channel
      Protein with a specific shape; open-close mechanism
      Ex. Osmosis and ligand-gated channels
      ACTIVE Transport
      REQUIRES Energy
      Goes Against Conc. Gradient
      Involves “transporter” membrane protein and ENERGY (ATP)
    • Osmosis
      Water (H2O) can pass easily through most biological membranes
      Diffusion of Water through a semi-permeable membrane
      Small molecules of water can sometimes diffuse across easily (no protein needed)
      What does “aqua” mean???
      Protein in cell membrane that allows water through (speeds up diffusion of water across the membrane)
      Type of Facilitated diffusion (more on this later)
    • How Osmosis works…
      We have water molecules and some other molecules, let’s say sugar
      If we have more water on one side of the membrane (HIGH conc. of H2O), then the water will diffuse across…
      Membrane will let water thru but not sugar
      Water can move back and forth (not sugar)
    • Water moves from areas of HIGH conc. To areas of LOW conc.
      Water moves across till equilibrium is reached
      when conc. Of both solutions is equal
      Hypertonic: “above strength”
      When we begin with more sugar in water
      More concentrated sugar solution on side A
      Hypotonic: “below strength”
      When we end with less sugar
      Dilute sugar solution on side A
    • Osmotic Pressure
      Central vacuole fills with water and exerts and out ward pressure on cell membrane and cell wall
      Cell wall does NOT allow cell to expand past a certain size
      • Osmoregulation
      • means by which cells keep the concentration of cell cytoplasm or blood at a suitable concentration.
    • Problems in Plant Cell
    • Osmotic Pressure
      Pressure exerted by osmosis on the HYPERTONIC side of a semi-permeable membrane
      Think about blowing up a balloon…
      Can cause serious problems for cell
      Cell is full of sugar, salts, proteins, molecules
      Inside of cell is Hypertonic
      Osmotic pressure should make fresh water go…?
      In or Out?
      Cell will become inflated/swollen
      Too much cell will burst like a balloon
    • Why don’t all our cells burst?
      What are our cells (animal) contained in?
      Fresh water?
      No…..blood or other fluids, which are ISOTONIC
      The conc. Of sugars, salts, proteins and molecules in these fluids is the same as the conc. in the cell
      Bacteria and plant cells
      They DO come in contact with fresh water…what do they have PROTECTING them?
      Prevent cells from expanding even when there’s a lot of osmotic pressure
      But, cell walls are prone to injuries when there is too much osmotic pressure
    • Which is a RBC in isotonic solution?
      RBC in hypertonic solution?
      RBC in hypotonic solution?
    • How do big molecules diffuse across a membrane so quickly if the membrane is selectively permeable?
    • Problems for diffusion…
      Things too large (like Glucose!)
      Charged molecules and Polar molecules
      Opposites attract but likes do not…
      These all present serious problems for things getting across membranes…
    • Facilitated Diffusion
      What does facilitate mean?
      Proteins are the extra help
      “escorts” across the membrane
      We call these protein channels…
      Allow specific things thru
    • Facilitated Diffusion
      • takes place through proteins, or assemblies of proteins, embedded in the plasma membrane
    • Facilitated Diffusion (continued)
      Still diffusion so we only see it from high concentration to low
      Does NOT require energy
    • What about when we want to go against the concentration?
      (From low concentration to high?)
    • What do we need???
    • ACTIVE transport
      Process that moves molecules against the concentration gradient
      Requires ENERGY
      A protein pumps small molecules and ions across a cell membrane against the conc. Gradient
      Direct and Indirect Active transport (see animation)
      Direct: every 3 Na+ ions pumped across for every 2 K+ ions
      Indirect: Build up of ions on one side opens up another channel to shuttle in other molecules
      Electrochemical gradient
      membrane potential (cell membrane is negative)
      To pump large molecules and clumps…
      2 other processes:
      The can change shape of membrane
    • Types of Active transport
      Molecular Transport (Direct and Indirect)
      When small ions and molecules are carried across membrane
      Endo- means….
      -Cyto- means…
      -sis mean….
      Exo- means….
      -Cyto- means…
      -sis mean….
    • Molecular Transport
      Proteins are used to pump small molecules and ions across membrane even against the conc. Gradient
      The cell devotes a lot of ENERGY to pumping things across membrane
      Potassium, calcium, and sodium are some things that need to pumped across
    • Build up of Na+ ions on one side of membrane from Na+/K+ pump
      Now Na+ will flow thru another channel that allows one glucose in too!
      Pretty convenient!
    • Endocytosis
      When cells need to take in large material
      Process of taking material into the cell by process of infolding, or pockets, of the cell membrane
      Pocket breaks loose from cell membrane and forms a vacuole or vesicle inside the cell
      Two Types…
    • Two types of endocytosis:
      1. Phagocytosis
      “cell eating”
      Extensions of cytoplasm surround the particle and package it within a food vacuole
      Cell then engulfs the package
      2. Pinocytosis
      “cell drinking”
      When cell needs to take up liquid
      Tiny pockets in cell membrane form
      Fill with liquid
      Then pinch off to form vacuoles inside of cell
    • Exocytosis
      Exo- means…
      Cyto means…
      Sis means…
      When cell releases large amounts of material
      Excretes stuff
      Membrane of vacuole surrounding particle inside cell fuses with the cell membrane
      The contents in vacuole are then forced out of the cell
      We see this in removal of water by contractile vacuoles