Cell membrane, transport. Prof. Gábor Szabó, 2017

Transcription

1 Cell membrane, transport Prof. Gábor Szabó, 2017

2 This lecture: Essential Cell Biology: chapters All the pages are required, except: ion channels, the pumps and mechanisms relevant to Ca, osmo- and ph regulation, also included in this chapter of the book, will be discussed in other lectures Text briefly describing the various membrane transporters discussed in this lecture is downloadable from our website! Together with the - marked lecture slides, that text is required material for the tests and exam!

3 Keywords amphiphylic (amphipathic) compounds lipid bilayer electrochemical gradient lipid-water partitioning coefficient Henderson-Hasselbach equation and its meaning facilitated diffusion carrier mediated passive transport passive and active transport coupled transport (secondary active) transport, examples of (Na/glucose and Na/Ca) Na/K pump, glucose uniport P-type, V-type transporters

4 Lipid bilayer 5 nm Functions of the plasmamembrane: barrier transport signal transduction Composition: % lipid % protein 10 % carbohydrate

5 Glycocalix Glycolipids, glycoproteins Actin cell cortex

6 Membrane proteins RBC: ~50 membrane proteins

7 ( Gram-negative ) bacteria have two cell membranes outer membrane: porins render it permeable inner membrane: transporters Lodish, Fig Alberts, Fig

8 Lipid synthesis and steady-state composition of cell membranes Major differences between organelles Mitochondria have bacterial lipids. Low cholesterol in Mit/ER/NE site of synthesis Nat. Rev. Mol. Cell. Biol. 2008

9 Asymmetric lipid composition Asymmetric lipid composition PS exposure on the surface of dying cells: eat-me signal for the phagocytes curvature 1. lipid incorporation into cytoplasmic leaflet 2. selective retention 3. flippases /floppases scramblases

10 Lipid shape and supramolecular organization (polymorphism). curvature Kai Simons, and Julio L. Sampaio Cold Spring Harb Perspect Biol 2011;3:a by Cold Spring Harbor Laboratory Press

11 Cytosolic and exoplasmic surface

12 Mobility may be restricted by clustering and molecular fences

13 Examples of heterogenous distribution of proteins in the plasma membrane of mammalian cells. (PMC /figure/F4/)

14 * Cell 2015! Transbilayer lipid interactions mediate nanoclustering of lipid-anchored proteins*.

15 Intimate relationship with the cell cortex Intracellular side RBC

16 cell cortex Cell shape is determined by the cytoplasm mutation ES HS altered morphology Defects that interrupt the vertical spectrin interactions Figure are the biochemical 4. Red cell morphology. and molecular Hereditary basis for hereditary spherocytosis spherocytosis (HS), (HS; top whereas panel); defects nonhemolytic in horizontal hereditary interactions elliptocytosis cause hereditary (HE; elliptocytosis middle panel); (ES). elliptocytes, poikilocytes, and fragmented red cells in hemolytic HE (bottom panel). BLOOD, 2008, 112(10) BLOOD, 2008, 112(10)

17 Membrane fluidity - permeability, deformability, regenerative capacity rso RBC ghost hypotony normotony iso

18 Transport

19 Categories of membrane transport, according to Membrane structure lipid bilayer complete biological membrane Number of different transported substances/direction of transport uniport symport, antiport Energetics passive active Transported substance solubility hydrophylic hydrophobic C R = C m aq > 1

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21 Lipid bilayers (arteficial membranes) 5-8 nm

22 Vesicles and MBLs

23 Hundertwasser, Vienna

24 Real membranes: passive and active transport

25 Carrier-mediated - passive - transport uniport. mechanism resembles that of the ionophore Valinomycin K +

26 Main categories of active transport Secondary active transporters, carriers symport antiport P V F ABC Na/K* Pgp,etc vacuolar mitochondrial * The Na/K-ATPase is also antiport by directionality, but it is not a coupled/secondary active transporter; it is a P-type pump.

27 Intestinal glucose transport What do you expect to occur as a result of inhibiting the Na/Kpump?

28 Why is intestinal glucose transport unidirectional (rectified)? Why do coupled transport processes depend on transmembrane Na + gradient? ~ 30% of total energy consumption in the cell!

29 A rise in the intracellular Ca2+ concentration causes muscle cells to contract. In addition to an ATPdriven Ca2+ pump, muscle cells that contract quickly and regularly, such as those of the heart, have an additional type of Ca2+ pump an antiport that exchanges Ca2+ for extracellular Na+ across the plasma membrane. The majority of the Ca2+ ions that have entered the cell during contraction are rapidly pumped back out of the cell by this antiport, thus allowing the cell to relax. Ouabain and digitalis are used for treating patients with heart disease because they make heart muscle cells contract more strongly. Both drugs function by partially inhibiting the Na+ pump in the plasma membrane of these cells. Can you propose an explanation for the effects of the drugs in the patients? What will happen if too much of either drug is taken?

30 Categories of transport according to solubility of S : A. hydrophylic substrates B. hydrophobic substrates C R = C m aq > 1

31 Transport of hydrophobic molecules Passive R (lipid / water partition coeff.) i.c. partition - Henderson-Hasselbach eq. Active ph = pk + log(m/m+) ABC (ATP binding casette) transporters Other transporters

32 1. lipid-water partition coeff. determines the efficiency of general anaesthetics ~ minimal effective cc. P ~lipid-water partition coeff.

33 Conformation of proteins is sensitive to the distribution of lateral pressure across the membrane

34 ion channels

35 The lipid-water partition coefficient may be ph-dependent R-NH 3 + lysosome ph 5 R-NH 2 R-NH 3 + R-NH 2 cytoplasm ph 7

36 Daunorubicin distribution in cytoplasts Selwyn J. Hurwitz et al. Blood 1997;89: by American Society of Hematology

37 Live cells incubated simultaneously with MitoTracker Deep Red FM, LysoTracker Green DND-26, and Hoechst (Invitrogen TM )