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LECTURE PRESENTATIONS
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson^ For CAMPBELL BIOLOGY, NINTH EDITION
Lectures by
Erin Barley
Kathleen Fitzpatrick
Membrane Structure and
Function
Chapter 7
Fig. 7- Fig. 7- Hydrophilic head WATER Hydrophobic tail WATER
Cellular membranes are fluid
mosaics of lipids and proteins
Membrane Models: Scientific
Inquiry
Fig. 7- Phospholipid bilayer Hydrophobic regions of protein Hydrophilic regions of protein
Fig. 7-
TECHNIQUE
Extracellular
layer
Knife Proteins^ Inside of extracellular layer
RESULTS
Inside of cytoplasmic layer
Plasma membrane Cytoplasmic layer
Fig. 7- Lateral movement (~10 (^7) times per second) Flip-flop (~ once per month) (a) Movement of phospholipids (b) Membrane fluidity Fluid Viscous Unsaturated hydrocarbon tails with kinks Saturated hydro- carbon tails (c) Cholesterol within the animal cell membrane Cholesterol Membrane Fluidity Fig. 7- Membrane proteins Mouse cell (^) Human cell Hybrid cell Mixed proteins after 1 hour Do membrane proteins move? Fig. 7-5c Cholesterol (c) Cholesterol within the animal cell membrane Cholesterol modulates membrane fluidity
Fig. 7- ER (^1) Transmembrane glycoproteins Secretory protein Glycolipid Golgi apparatus 2 Vesicle 3 4 Secreted protein Transmembrane glycoprotein Plasma membrane: Cytoplasmic face Extracellular face Membrane glycolipid Synthesis and Sidedness of Membranes Fig. 7- ATP
Hydrophobic - dissolve in the lipid bilayer
Polar molecules (e.g. sugars) do not cross the membrane easily
“Transport proteins” allow passage of hydrophilic substances
--channel proteins, hydrophilic channel that select molecules or ions
can use as a tunnel
aquaporins facilitate the passage of water
-- carrier proteins , bind to molecules and shuttle them across the
Plasma membrane is selectively permeable Fig. 7-11 (^) Molecules of dye (^) Membrane (cross section) WATER Net diffusion Net diffusion Equilibrium (a) Diffusion of one solute Net diffusion Net diffusion Net diffusion Net diffusion Equilibrium Equilibrium (b) Diffusion of two solutes
Lower concentration
of solute (sugar)
Fig. 7-
H 2 O
Higher concentration
of sugar
Selectively permeable
membrane
Same concentration
of sugar
Osmosis
Effects of Osmosis on Water Balance
Fig. 7- Hypotonic solution (a) Animal cell (b) Plant cell H 2 O Lysed H 2 O Turgid (normal) H 2 O H 2 O H 2 O H 2 O Normal Isotonic solution Flaccid H 2 O H 2 O Shriveled Plasmolyzed Hypertonic solution Fig. 7- Filling vacuole 50 μm (a) A contractile vacuole fills with fluid that enters from a system of canals radiating throughout the cytoplasm. Contracting vacuole (b) When full, the vacuole and canals contract, expelling fluid from the cell. Water Balance of Cells with Walls
- Cell walls help maintain water balance
- Plant cell in hypotonic solution swells until the wall opposes uptake; the cell is now turgid (firm)
- If a plant cell and its surroundings are isotonic, there is no net movement of water into the cell; the cell becomes flaccid (limp), and the plant may wilt
- In a hypertonic environment, plant cells lose water; eventually, the membrane pulls away from the wall, a usually lethal effect called plasmolysis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Facilitated Diffusion: Passive Transport Aided by Proteins
Fig. 7-17 Passive transport
Diffusion Facilitated diffusion
Active transport
ATP
Ion Pumps Maintain Membrane Potential
- Membrane potential - voltage difference across a membrane -distribution of positive and negative ions
- electrochemical gradient-
- -ion’s concentration gradient
- -membrane potential Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings ......\Desktop\pump-cycle-medium.mov Fig. 7- Proton pump
- – – – – –
ATP H+ H+ H+ H+ H+ H+ H+ H+ Diffusion Sucrose-H+^ of H+ cotransporter Sucrose Sucrose Cotransport: Coupled Transport by a Membrane Protein Concept 7.5: Bulk transport across the plasma membrane occurs by exocytosis and endocytosis
- Small molecules and water enter or leave the cell through the lipid bilayer or via transport proteins
- Large molecules, such as polysaccharides and proteins, cross the membrane in bulk via vesicles
- Bulk transport requires energy © 2011 Pearson Education, Inc.
Exocytosis
- In exocytosis , transport vesicles migrate to the membrane, fuse with it, and release their contents
- Many secretory cells use exocytosis to export their products © 2011 Pearson Education, Inc. Animation: Exocytosis Endocytosis
- In endocytosis , the cell takes in macromolecules by forming vesicles from the plasma membrane
- Endocytosis is a reversal of exocytosis, involving different proteins
- There are three types of endocytosis
- Phagocytosis (“cellular eating”)
- Pinocytosis (“cellular drinking”)
- Receptor-mediated endocytosis © 2011 Pearson Education, Inc. Animation: Exocytosis and Endocytosis Introduction
- In phagocytosis a cell engulfs a particle in a vacuole
- The vacuole fuses with a lysosome to digest the particle © 2011 Pearson Education, Inc. Animation: Phagocytosis
- In pinocytosis , molecules are taken up when extracellular fluid is “gulped” into tiny vesicles © 2011 Pearson Education, Inc. Animation: Pinocytosis
Fig. 7-UN Active transport: ATP You should now be able to:
- Define the following terms: amphipathic molecules, aquaporins, diffusion
- Explain how membrane fluidity is influenced by temperature and membrane composition
- Distinguish between the following pairs or sets of terms: peripheral and integral membrane proteins; channel and carrier proteins; osmosis, facilitated diffusion, and active transport; hypertonic, hypotonic, and Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings^ isotonic solutions
- Explain how transport proteins facilitate diffusion
- Explain how an electrogenic pump creates voltage across a membrane, and name two electrogenic pumps
- Explain how large molecules are transported across a cell membrane Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
