* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Cell membrane ppt Plasma mb ppt
Action potential wikipedia , lookup
Mechanosensitive channels wikipedia , lookup
Protein moonlighting wikipedia , lookup
Lipid bilayer wikipedia , lookup
Model lipid bilayer wikipedia , lookup
P-type ATPase wikipedia , lookup
Protein adsorption wikipedia , lookup
Theories of general anaesthetic action wikipedia , lookup
Intrinsically disordered proteins wikipedia , lookup
G protein–coupled receptor wikipedia , lookup
Protein–protein interaction wikipedia , lookup
Magnesium transporter wikipedia , lookup
Proteolysis wikipedia , lookup
SNARE (protein) wikipedia , lookup
Membrane potential wikipedia , lookup
Oxidative phosphorylation wikipedia , lookup
Signal transduction wikipedia , lookup
Cell-penetrating peptide wikipedia , lookup
Trimeric autotransporter adhesin wikipedia , lookup
Western blot wikipedia , lookup
List of types of proteins wikipedia , lookup
The Plasma Membrane Membrane Transport Figure 5.1 The Fluid Mosaic Model • Phospholipids- the main “fabric” – amphipathic= they have both hydrophilic AND a hydrophobic regions • Proteins- embedded in the phospholipid membrane – Also amphipathic – Determine the function of the membrane – Proteins are not distributed randomly or evenly, but rather according to function How fluid is fluid? • The membrane is held together my hydrophobic interactions-weaker than covalent bonds • Constant lateral movement • Proteins larger than lipids therefore move more slowly Viscosity • A measure of a fluid’s resistance to flow; how “thick” or “sticky” it is • Due to molecular makeup and internal friction • Honey is more viscous than water What determines a membrane’s viscosity? • Hydrocarbon tails on its phospholipids – Saturated- more viscous – Unsaturated- less viscous, more fluid • Temperature – Decrease in temp more viscous; may eventually solidify – Increase in temp less viscous; too fluid, cannot support proteins and their function What determines a membrane’s viscosity? • Cholesterol- helps membranes resist changes in fluidity with changes in temperature – High temps- restricts movement of phospholipids – Low temps- prevents phospholipids from packing together • Evolution – Membrane composition evolves to meet specific environmental needs • Cold Figure 5.5 Fluid Unsaturated tails prevent packing. Viscous Saturated tails pack together. (a) Unsaturated versus saturated hydrocarbon tails (b) Cholesterol reduces membrane fluidity at moderate temperatures, but at low temperatures hinders solidification. Cholesterol What determines a membrane’s viscosity? • Evolution – Membrane composition evolves to meet specific environmental needs • Cold water fish • Archea that live at 90°C (194°F) • Some alter their composition seasonally Membrane Proteins and Their Functions • The proteins within the phospholipid bilayer determine the function of the membrane. • Different cells different membrane proteins • Different organelles with a specific cell different membrane proteins Two Major Types of Proteins • Integral • Peripheral • Can you see the difference? Figure 5.2 Fibers of extracellular matrix (ECM) Glycoprotein Carbohydrate Glycolipid EXTRACELLULAR SIDE OF MEMBRANE Cholesterol Microfilaments of cytoskeleton Peripheral proteins Integral protein CYTOPLASMIC SIDE OF MEMBRANE Integral • Penetrates the membrane – Transmembrane- through to both surfaces – Partially embedded- only exposed on one surface • The embedded portions have hydrophobic amino acids, often in an α helix • Some have hydrophilic channels through them to allow for passage of substances through the membrane Figure 5.6 N-terminus helix C-terminus EXTRACELLULAR SIDE CYTOPLASMIC SIDE Peripheral • Not embedded • Bound to either surface – Extracellular matrix (outside) – Cytoskeletal elements (inside) • Provide extra support for the membrane Figure 5.2 Fibers of extracellular matrix (ECM) Glycoprotein Carbohydrate Glycolipid EXTRACELLULAR SIDE OF MEMBRANE Cholesterol Microfilaments of cytoskeleton Peripheral proteins Integral protein CYTOPLASMIC SIDE OF MEMBRANE 6 Major Functions of Plasma Membrane Proteins 1. 2. 3. 4. 5. 6. Transport Enzymatic activity Attachment to the cytoskeleton and ECM Cell-cell recognition Intercellular joining Signal transduction Figure 5.7 Enzymes ATP (a) Transport (b) Enzymatic activity (c) Attachment to the cytoskeleton and extracellular matrix (ECM) Signaling molecule Receptor Glycoprotein (d) Cell-cell recognition (e) Intercellular joining (f) Signal transduction Membrane Carbohydrates • Cell-cell recognition • Can be covalent bound to either lipids or proteins on the extracellular side of the membrane – Glycoproteins – Glycolipids • Act as markers to cells – Ex. ABO blood types distinguish Membrane Synthesis • Proteins and lipids- ER • Carbohydrates added –Golgi Selective permeability • 2 aspects of “selectivity” – The membrane takes up some small ions and molecules, but not others – Substances that are allowed through, do so at different rates • How does the membrane accomplish this selectivity? Figure 5.3 Form Follows Function Hydrophilic head WATER WATER Hydrophobic tail • Nonpolar substances= hydrophobic – Cross easily – Ex. Hydrocarbons, CO2 ,O2 • Ions & polar substances= hydrophilic – Hard to pass – Ex. Glucose, H2O, Na+, Cl– Ions especially have a hard time as they tend to be surrounded by a “shell” of water molecules Transport Proteins • Channel proteins vs. carrier proteins – Channel proteins create a channel through which hydrophilic substances may pass. Ex. Aquaporins – Carrier proteins hold onto substances, change shape and redeposit them on the other side Figure 5.14 EXTRACELLULAR FLUID 1 CYTOPLASM [Na] high [K] low [Na] low [K] high 2 6 3 5 4 ADP Directionality of transport • Controlled by – Passive transport • Diffusion • Osmosis • Facilitated diffusion – Active transport • Ion pumps, membrane potential • Cotransport – Bulk transport • Exocytosis • Endocytosis Active transport • Moves substances against their gradient; from an area of low concentration to one of high concentration • Requires energy- supplied by ATP • Allows cells to maintain a different environment inside vs. outside the cell An example is the sodiumpotassium pump Figure 5.14a EXTRACELLULAR [Na] high FLUID [K] low CYTOPLASM [Na] low [K] high 1 Cytoplasmic Na binds to the sodium-potassium pump. The affinity for Na is high when the protein has this shape. ADP 2 Na binding stimulates phosphorylation by ATP. Figure 5.14b 3 Phosphorylation leads to a change in protein shape, reducing its affinity for Na, which is released outside. 4 The new shape has a high affinity for K, which binds on the extracellular side and triggers release of the phosphate group. Figure 5.14c 5 Loss of the phosphate group restores the protein’s original shape, which has a lower affinity for K. 6 K is released; affinity for Na is high again, and the cycle repeats. Ion pumps maintain voltage across membranes • Membrane potential= the voltage across a membrane • Cytoplasmic side relatively negative • Creates electrical potential energy that drives passive transport of cations into the cell and anions out • Electrochemical gradient= chemical (concentration gradient) and electrical forces that drive diffusion across membranes Main electrogenic pumps • Animals– Sodium-potassium pump • Plants– Proton pump Figure 5.16 EXTRACELLULAR FLUID Proton pump CYTOPLASM Cotransport • A process by which one protein transports 2 molecules or ions at a time. It uses the diffusion of solute to force the other against it’s gradient. • It does not use ATP directly, but often is coupled with an ion pump that does use ATP Figure 5.17 Proton pump Sucrose-H cotransporter Diffusion of H Sucrose Sucrose Bulk Transport • Exocytosis • Endocytosis – Phagocytosis – Pinocytosis – Receptor-mediated endocytosis Figure 5.18 Phagocytosis Pinocytosis Receptor-Mediated Endocytosis EXTRACELLULAR FLUID Solutes Pseudopodium Plasma membrane Coat protein “Food” or other particle Food vacuole CYTOPLASM Coated pit Coated vesicle Receptor