* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Chapter 7 Membrane
Survey
Document related concepts
Biochemistry wikipedia , lookup
Magnesium transporter wikipedia , lookup
Theories of general anaesthetic action wikipedia , lookup
Protein adsorption wikipedia , lookup
G protein–coupled receptor wikipedia , lookup
Membrane potential wikipedia , lookup
SNARE (protein) wikipedia , lookup
Paracrine signalling wikipedia , lookup
Evolution of metal ions in biological systems wikipedia , lookup
Lipid bilayer wikipedia , lookup
Proteolysis wikipedia , lookup
Model lipid bilayer wikipedia , lookup
Western blot wikipedia , lookup
Cell-penetrating peptide wikipedia , lookup
Electrophysiology wikipedia , lookup
Cell membrane wikipedia , lookup
Transcript
Membrane Structure and Function Chapter 7 Overview: Life at the Edge • The plasma membrane selectively permeable Cell membranes • Phospholipids most abundant lipids in plasma membrane • amphipathic = hydrophobic and hydrophilic regions – Polar head – Hydrocarbon tails • Phospholipid Membrane Models: Scientific Inquiry Hydrophilic head WATER Hydrophobic tail WATER • 1935Davson and Danielli - bilayer model • 1972 Singer and Nicolson - fluid mosaic model – membrane mosaic of proteins dispersed within bilayer • Current model: mosaicism TECHNIQUE RESULTS Extracellular layer Proteins Knife Plasma membrane Inside of extracellular layer Cytoplasmic layer Inside of cytoplasmic layer Proteins embedded in bilayer Phospholipid bilayer Hydrophobic regions of protein Hydrophilic regions of protein The Fluidity of Membranes Phospholipids in membrane move laterally within bilayer rarely flip flop • Lipids, proteins, may move laterally Lateral movement (∼107 times per second) (a) Movement of phospholipids Flip-flop (∼ once per month) RESULTS Membrane proteins Mouse cell Mixed proteins after 1 hour Human cell Hybrid cell Membrane fluidity affected by: 1. Type of phospholipid Fluid Unsaturated hydrocarbon tails with kinks Viscous Saturated hydrocarbon tails 2. Temperature • cool gel – Tightly packed tails • warm fluid 3. Cholesterol • Stabilizes membrane fluidity with changing temperature FYI Cholesterol can compose ½ of the membrane Bacterial cell membranes do not contain cholesterol Plant cells do not contain much Cholesterol (c) Cholesterol within the animal cell membrane Membrane Proteins and Their Functions • Mosaic of proteins embedded in lipid bilayer • Proteins determine most of membrane’s functions Membrane Proteins Peripheral proteins – bound to _____________ of membrane Integral proteins – penetrate hydrophobic region – Transmembrane proteins Nterminus C-terminus 1. Receptor proteins for signal transduction • ex. Insulin receptor 2. Channel proteins for passage of molecules hydrophilic core • Hydrophilic core • Ex. Aquaporins 3. Transport proteins Ex. Glucose transporter shuttles glucose across membrane Signaling molecule Enzymes ATP (a) Transport Receptor Signal transduction (b) Enzymatic activity (c) Signal transduction Glycoprotein (d) Cell-cell recognition (e) Intercellular joining (f) Attachment to the cytoskeleton and extracellular matrix (ECM) 4. Cell-cell recognition • Glycoproteins – Carbohydrates attached to proteins mucin 5. Intercellular joining proteins Ex. gap junctions allow passage of ions and small molecules from cell to cell 6. Extracellular matrix proteins 7. Membrane enzymes Six major functions of membrane proteins: – Transport – Enzymatic activity – Signal transduction – Cell-cell recognition – Intercellular joining – Attachment to the cytoskeleton and extracellular matrix (ECM) Selective permeability • Plasma membrane regulates cell molecular traffic Permeability of Lipid Bilayer • Hydrophobic molecules dissolve in bilayer and pass through membrane rapidly – O2, CO2, NO, steroids, nanoparticles O2 CO2 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Hydrophilic (polar) molecules do not cross easily – sugar, water, ions Passive transport = no energy used molecules move randomly A. Diffusion • Molecules diffuse down their concentration gradient from high to lower concentration until equilibrium What molecules can diffuse across the cell membrane? Answer: O2, CO2, urea Net diffusion Net diffusion (b) Diffusion of two solutes Net diffusion Net diffusion Equilibrium Equilibrium • B. Osmosis is diffusion of water across a selectively permeable membrane • Water diffuses across membrane from region of higher water concentration to the region of lower water concentration until equilbrium Lower concentration of sugar) Higher Concentration of sugar Same concentration of sugar H2O Selectively permeable membrane Osmosis Water Balance of Cells Without Walls • Tonicity =ability of solution to cause cell to gain or lose water • Isotonic solution: Solute concentration same as in cell – no net water movement across membrane • Hypertonic solution: Solute concentration greater than inside cell – cell loses water • Hypotonic solution: Solute concentration is less than inside cell – cell gains water Solution type? Isotonic, hypotonic, hypertonic? Hypotonic solution H2O Isotonic solution H2O Hypertonic solution H2O H2O (a) Animal cell Lysed Normal Shriveled How do cells deal with changing external water concentrations? • Osmoregulation= control of water balance • Ex. Paramecium video – pond water is _____________ to the protista – contractile vacuole 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 in plants (cell wall) • Isotonic solution no net movement of water into cell – flaccid (limp) • Hypotonic solution cell (vacuole) swells – cell wall opposes uptake turgid (firm) • Hypertonic lose water; membrane pulls away from wall – plasmolysis (lethal) Hypotonic solution H2O Isotonic solution H2O H2O Hypertonic solution H2O Flaccid Plasmolyzed (b) Plant cell Turgid (normal) C. Facilitated Diffusion: Passive Transport aided by proteins • Channel proteins • Carrier proteins What molecules use facilitated diffusion to cross membrane? Answer: glucose, sodium ions, chloride ions, water EXTRACELLULAR FLUID Channel protein Solute CYTOPLASM (a) A channel protein Carrier protein (b) A carrier protein Solute Active transport • Energy (ATP) required to move solutes against their gradients (from lower to higher conc. !) Pumps are membrane proteins FYI: Ex. sodium-potassium pump (an enzyme) All animals Nobel prize 1997 (Jens Skou) Uses 1/3 of cells total energy production Provides driving force for other cell processes (secondary transport, volume, gradients) Examine the figure: EXTRACELLULAR FLUID Na+ Na+ high outside cell K+ low Na+ low inside cell K+ high According to diffusion? [Na+] high [K+] low Na+ CYTOPLASM 1 Na+ [Na+] low [K+] high Cytoplasmic Na+ binds to the sodium-potassium pump. 1. Cytoplasmic Na+ binds to pump 2. ADP phosphorylated to ATP Na+ Na+ Na+ What is ATP? P ADP ATP Na+ binding stimulates phosphorylation by ATP. 2 + Na Na+ 3. Na+ out of cell + Na Na+ shape change of pump Against conc. grad. + Na Na+ PP Phosphorylation Phosphorylation causes causes the the protein protein to to change change its its ++ is expelled to shape. Na shape. Na is expelled to the the outside. outside. 33 4. Extracellular K+ binds to pump ATP used P P 4 K+ binds on the extracellular side and triggers release of the phosphate group. 5+6 K+ inside cell Pump animation Step by step Shape change Passive transport Active transport Review the difference passive vs active transport ATP Diffusion Facilitated diffusion NO ATP IS USED WHICH ONE REPRESENTS THE CHANNEL PROTEIN? Why do cells need pumps? a. Maintain membrane potential = voltage difference across membrane Inside of cell more electronegative than out = negative membrane potential – ATP EXTRACELLULAR FLUID + – + H+ H+ Proton pump H+ – + H+ H+ – + CYTOPLASM – H+ + b. Maintain electrochemical gradients – chemical = concentration gradient – electrical = membrane potential Bulk transport • Exocytosis – To secrete products from cell – Vesicles fuse with membrane 2. Endocytosis cell takes in macromolecules by forming vesicles from membrane a. Phagocytosis – for large particle Vesicle fuses with lysosome to digest particle PHAGOCYTOSIS EXTRACELLULAR FLUID 1 µm CYTOPLASM Pseudopodium Pseudopodium of amoeba “Food” or other particle Bacterium Food vacuole Food vacuole An amoeba engulfing a bacterium via phagocytosis (TEM) b. Pinocytosis – for fluids/small molecules PINOCYTOSIS 0.5 µm Plasma membrane Pinocytosis vesicles forming (arrows) in a cell lining a small blood vessel (TEM) Vesicle c. receptor-mediated endocytosis, ligand binds to receptor vesicle RECEPTOR-MEDIATED ENDOCYTOSIS Coat protein Receptor Coated vesicle Coated pit Ligand