Lesson 3: Plasma Membrane Structure and Transport (PDF)

Lesson 3 PLASMA MEMBRANE: structure and transport © Copyright Universidad Europea. Todos los derechos reservados Cell motility  Index  FEATURES A...

Lesson 3 PLASMA MEMBRANE: structure and transport © Copyright Universidad Europea. Todos los derechos reservados Cell motility  Index  FEATURES AND FUNCTIONS  THE SINGER AND NICOLSON MODEL  STRUCTURE AND COMPOSITION  TRANSPORT ACROSS MEMBRANE © Copyright Universidad Europea. Todos los derechos reservados  CONCEPT Nuclear envelope PLASMA MB CONCEPT OF BIOLOGICAL MEMBRANE  The cell and its organelles (mitochondria, nucleus, Golgi apparatus...) are surrounded by biological membranes  All membranes have a common base structure, with the same components  They are very thin, not visible under an optical microscope  The membrane that surrounds the cell is called the PLASMA MEMBRANE Mitochondrial mb © Copyright Universidad Europea. Todos los derechos reservados © Copyright Universidad Europea. Todos los derechos reservados  PLASMA MEMBRANE FUNCTION PLASMA MB PLASMA MEMBRANE FUNCTION  Regulates transport between the cell and the outside  Mediates interactions between cells  Separates and protects your components from the external environment © Copyright Universidad Europea. Todos los derechos reservados  CHEMICAL COMPOSITION OF THE PLASMA MEMBRANE  All plasma membranes have the same components  They appear in different proportions depending on the membranes  Asymmetric distribution CARBOHYDRATES(~ 10% *) LIPIDS (~ 45% *) PROTEINS (~ 45% *) * % correspondiente a glóbulos rojos © Copyright Universidad Europea. Todos los derechos reservados  THE FLUID MOSAIC MODEL (Singer and Nicolson) Consider that...  The membrane is a fluid mosaic formed by a lipid bilayer in which proteins are embedded in it, interacting with each other and with lipids. Both proteins and lipids can move laterally.  The membrane is an amphipathic structure with the ionic and highly polar groups protruding from the membrane into the aqueous phase, and the nonpolar groups largely buried in the hydrophobic interior of the membrane.  The membranes are an asymmetrical structure in terms of distribution, mainly of carbohydrates, which are only found on the outside. © Copyright Universidad Europea. Todos los derechos reservados  THE FLUID MOSAIC MODEL (Singer and Nicolson) © Copyright Universidad Europea. Todos los derechos reservados  THE FLUID MOSAIC MODEL "FLUID mosaic" © Copyright Universidad Europea. Todos los derechos reservados  CHEMICAL COMPOSITION OF THE PLASMA MEMBRANE LIPIDS CHARACTERISTICS  They are part of all biological membranes  They appear in different proportions depending on the membranes  They are amphipathic molecules (hydrophilic+phobic) TYPES OF LIPIDS 1. 1. FOSFOLÍPIDOS 3. 2. COLESTEROL 3. GLUCOLÍPIDOS 2. © Copyright Universidad Europea. Todos los derechos reservados  CHEMICAL COMPOSITION OF THE PLASMA MEMBRANE LIPIDS  In an aqueous environment, the lipid bilayer spontaneously closes in on itself to form enclosed compartments Polar heads (hydrophilic) in contact with aqueous medium Nonpolar tails (hydrophobic) protected from water © Copyright Universidad Europea. Todos los derechos reservados © Copyright Universidad Europea. Todos los derechos reservados  CHEMICAL COMPOSITION OF THE PLASMA MEMBRANE Why do these matter for plasma membrane? Cholesterol If Tª ↑: prevents phospholipids from Provides flexibility moving too much and mechanical If Tª ↓: prevents phospholipids to be stability. too close The UNSATURATION of fatty acids Provides fluidity to membranes The greater the degree of unsaturation of the chains of the fatty acids  the greater the fluidity (4) © Copyright Universidad Europea. Todos los derechos reservados (4)  CHEMICAL COMPOSITION OF THE PLASMA MEMBRANE PROTEINS CHARACTERISTICS  Amphipathic molecules  Responsible for the concentration of ions between two compartments CLASSIFICATION 1. INTEGRAL PROTEINS, usually TRANSMEMBRANE PROTS 2. PERIPHERAL PROTEINS © Copyright Universidad Europea. Todos los derechos reservados  CHEMICAL COMPOSITION OF THE PLASMA MEMBRANE Remember: PROTEINS Proteins are made up of aminoacids (C1) FUNCTIONS 1) Transport of molecules 2) Part of cell-to-cell-binding structures to form tissues 3) Connection of the membrane to the cytoskeleton 4) Receptors 5) Cell-cell recognition and message transmission 6) Reactions catalysts © Copyright Universidad Europea. Todos los derechos reservados  CHEMICAL COMPOSITION OF THE PLASMA MEMBRANE CARBOHYDRATES CHARACTERISTICS  Protein-bound  GLYCOPROTEINS  Lipid-bound  GLYCOLIPIDS  Asymmetric distribution: always on the outside surface of the membrane  They form the cellular GLYCOCALYX © Copyright Universidad Europea. Todos los derechos reservados < Glycocalyx  CHEMICAL COMPOSITION OF THE PLASMA MEMBRANE CARBOHYDRATES FUNCTIONS  Cellular recognition  Immune properties (blood types ABO) A: it has N-acetylgalactosamine on the surface B It has Galactose on the surface © Copyright Universidad Europea. Todos los derechos reservados  REVIEW THIS PART OF THE CHAPTER WITH THE AMOEBA SISTERS © Copyright Universidad Europea. Todos los derechos reservados  TRANSPORT ACROSS THE PLASMA MEMBRANE Why is membrane transport necessary? Cellular nutrition (introducing glucose, fatty acids...) Excretion (removing waste products) Cell communication (pouring molecules that other cells receive) © Copyright Universidad Europea. Todos los derechos reservados  TRANSPORT ACROSS THE PLASMA MEMBRANE ESQUEMA DE LOS TIPOS DE TRANSPORTE TPT OF SMALL MOLECULES PASSIVE TRANSPORT ACTIVE TRANSPORT No ENERGY expenditure ENERGY expenditure FACILITATED SIMPLE DIFFUSION PRIMARY SECONDARY DIFFUSION TPT OF LARGE PARTICLES ENTRY EXIT ENTRY & EXIT PINOCYTOSIS RECEPTOR- PHAGOCYTOSIS EXOCYTOSIS TRANSCITOSIS MEDIATED ENDOCYTOSIS © Copyright Universidad Europea. Todos los derechos reservados  TRANSPORT ACROSS THE PLASMA MEMBRANE SMALL MOLECULE TRANSPORT  The lipid bilayer is semipermeable (selective permeability) SMALL NONPOLAR Gases (O2, CO2) pass freely through the membrane MOLECULES UNCHARGE D POLAR SMALL MOLECULES Many nutrients (glucose, aa) are too large to cross the lipid bilayer LARGER UNCHARGE D POLAR How do they get into the cell? MOLECULES Using transport proteins IONS Bicapa lipídica © Copyright Universidad Europea. Todos los derechos reservados  TRANSPORT ACROSS THE PLASMA MEMBRANE ESQUEMA DE LOS TIPOS DE TRANSPORTE SMALL SOLUTES PASSIVE TRANSPORT ACTIVE TRANSPORT ATP ATP No energy expenditure ENERGY expenditure FACILITATED SIMPLE DIFFUSION PRIMARY SECONDARY DIFFUSION (1) © Copyright Universidad Europea. Todos los derechos reservados  TRANSPORT ACROSS THE PLASMA MEMBRANE ESQUEMA DE LOS TIPOS DE TRANSPORTE WHAT IS DIFFUSION? ATP Net movement of particles down its concentration gradient until equilibrium (1) © Copyright Universidad Europea. Todos los derechos reservados  TRANSPORT ACROSS THE PLASMA MEMBRANE ESQUEMA DE LOS TIPOS DE TRANSPORTE WHAT IS DIFFUSION? ATP Characteristics Types:  Passive transport  Dialysis  particle  No energy expenditure movement across a semipermeable  In favor of gradient membrane  Osmosis  water movement across a semipermeable membrane (1) © Copyright Universidad Europea. Todos los derechos reservados  TRANSPORT ACROSS THE PLASMA MEMBRANE REVIEW OSMOSIS WITH THE AMOEBA SISTERS ESQUEMA DE LOS TIPOS DE TRANSPORTE OSMOSIS can cause alterations of cell volume, affecting the normal ATP functioning of the cell © Copyright Universidad Europea. Todos los derechos reservados  TRANSPORT ACROSS THE PLASMA MEMBRANE ESQUEMA DE LOS TIPOS DE TRANSPORTE PASSIVE TRANSPORT Down to gradient ATP  No energy expenditure SIMPLE DIFFUSION FACILITATED DIFFUSION  No transport protein needed  Mediated by transport proteins 1) Transporters 2) Channels ANIMATIONS © Copyright Universidad Europea. Todos los derechos reservados  TRANSPORT ACROSS THE PLASMA MEMBRANE 1) Transporters There is interaction between the molecule and the transporter Ex: incorporation of glucose into the cell © Copyright Universidad Europea. Todos los derechos reservados  TRANSPORT ACROSS THE PLASMA MEMBRANE 2) Channels A channel is formed inside the protein Ions pass through it (Na+, Ca2+, K+…) Open channels Voltage-gated Ligand-Activated channels Channels © Copyright Universidad Europea. Todos los derechos reservados  TRANSPORT ACROSS THE PLASMA MEMBRANE 2) Channels Example of pathology: non-functional Cl- channel in patients with cystic fibrosis It does not transport Cl - dense mucus, respiratory failure, inflammation... © Copyright Universidad Europea. Todos los derechos reservados  GO OVER THE Na-K pump TRANSPORT ACROSS THE PLASMA MEMBRANE with amoebas sisters ATP ESQUEMA ACTIVE DE LOS TIPOS DE TRANSPORTE TRANSPORT  With energy expenditure  Against gradient  Protein-mediated PRIMARY SECONDARY © Copyright Universidad Europea. Todos los derechos reservados  TRANSPORT ACROSS THE PLASMA MEMBRANE 1) Primary Active Transport A protein (pump) uses ATP to transport molecules against gradient  Eg: Na+/K+ pump  Maintains adequate concentration of ions on both sides of the membrane  Generates the resting membrane potential  Allows the cell to be alive Na+/K + pump © Copyright Universidad Europea. Todos los derechos reservados  TRANSPORT ACROSS THE PLASMA MEMBRANE 2) Secondary Active Transport To move against its gradient, a molecule takes advantage of another molecule moving down its gradient  E.g.: Na+/glucose cotransport to absorb glucose in the intestinal epithelium  Na+ is transported down to gradient  The potential energy of the Na+ gradient is used to pump Glu against its gradient © Copyright Universidad Europea. Todos los derechos reservados  TRANSPORT ACROSS THE PLASMA MEMBRANE ESQUEMA DE LOS TIPOS DE TRANSPORTE SMALL MOLECULE TRANSPORT: SUMMARY © Copyright Universidad Europea. Todos los derechos reservados  TRANSPORT ACROSS THE PLASMA MEMBRANE What type of transport does each number mark? © Copyright Universidad Europea. Todos los derechos reservados  TRANSPORT ACROSS THE PLASMA MEMBRANE ESQUEMA TRANSPORT DE LOS TIPOS DE TRANSPORTE OF LARGE PARTICLES ENTRY EXIT ENTRY & EXIT PINOCYTOSIS RECEPTOR- PHAGOCYTOSIS EXOCYTOSIS TRANSCYTOSIS MEDIATED ENDOCYTOSIS  Nonspecific  Specific  Specific  No change in content © Copyright Universidad Europea. Todos los derechos reservados  TRANSPORT ACROSS THE PLASMA MEMBRANE ENTRY: The particle is enclosed in a portion of mb  folds inward  vesicle + particle ENDOCYTOSIS 1) Pinocytosis 2) R-mediated 3) Phagocytosis Nonspecific uptake endocytosis Selective uptake of extracelular of pathogens, Specific uptake of liquid damaged cells… target substances Carried out by (hormones, immune cells nutrients…)  Cholesterol-LDL uptake  Neutrófilo fagocitando bacteria © Copyright Universidad Europea. Todos los derechos reservados  TRANSPORT ACROSS THE PLASMA MEMBRANE Neutrophil phagocytosing a bacterium © Copyright Universidad Europea. Todos los derechos reservados  TRANSPORT ACROSS THE PLASMA MEMBRANE EXIT: Vesicle + material to be taken out  fusión with PM  material EXOCYTOSIS outside Fusión  Neurotransmitter release by neurons © Copyright Universidad Europea. Todos los derechos reservados  TRANSPORT ACROSS THE PLASMA MEMBRANE ENTRY + EXIT: Endocytosis  vesicle goes pass the cell 