Biología general de la membrana plasmática Prof. Bernal Gerardo Garro Mora UCR
Las membranas celulares son estructuras muy complejas, cuyos elementos estructurales difieren según el tipo de organismo, aunque siguen el patrón general del mosaico fluido. Un ejemplo de estas especializaciones es la membrana que forma parte de la envoltura celular de las bacterias Gram positivas, como la de Staphylococcus aureus, que acá se muestra
Modelo del mosaico fluido de Singer y Nicholson (1974)
extracellular matrix Estructura básica de la membrana plasmática extracellular fluid (outside) attachment protein binding site receptor protein phospholipid glycoprotein phospholipid bilayer pore carbohydrate protein transport protein cholesterol recognition protein enzyme cytoplasm (inside) cytoskeleton Fig. 5-1
Anclaje a la ECM y al citoesqueleto
Estructura de un fosfolípido de membrana head (hydrophilic) tails (hydrophobic) Fig. 5-2
Author Animation: Plasma Membrane Structure
La bicapa fosfolipídica de la membrana celular phospholipid extracellular fluid (watery environment) hydrophilic heads bilayer hydrophobic tails hydrophilic heads cytoplasm (watery environment) Fig. 5-3
more fluid less fluid Las insaturaciones de losácidosgrasosincrementanla fluidezde membrana Fig. 5-4
Dos hemicapas: concepto de asimetría de membrana
Author Animation: Cell Membranes
Activaciónde receptoresproteicos (extracellular fluid) hormone 1 A hormone binds to the receptor receptor (cytoplasm) 2 Hormone binding activates the receptor, changing its shape 3 The activated receptor stimulates a response in the cell Fig. 5-5
Difusión 1 A drop of dye is placed in water 2 Dye molecules diffuse into the water; water molecules diffuse into the dye 3 Both dye molecules and water molecules are evenly dispersed drop of dye water molecule Fig. 5-6
Osmosis: el movimiento del solvente a través de la membrana
Difusión facilitada por proteínas de membrana
Table 5-1
Author Animation: Passive Diffusion
Tiposde difusióna travésde membrana (extracellular fluid) O 2 Cl water glucose phospholipid bilayer (cytoplasm) channel protein aquaporin carrier protein (a) Simple diffusion through the phospholipid bilayer (b) Facilitated diffusion through channel proteins (c) Osmosis through aquaporins or the phospholipid bilayer (d) Facilitated diffusion through carrier proteins Fig. 5-7
Resumen de fenómenos de difusión a nivel de membrana
Author Animation: Facilitated Diffusion
Author Animation: Diffusion
Efecto de la concentración de solutos sobre la ósmosis No net flow of water Water flows out; the balloon shrinks Water flows in; the balloon expands (a) A balloon in an isotonic solution (b) A balloon in a hypertonic solution (c) A balloon in a hypotonic solution Fig. 5-8
Author Animation: Osmosis
Efectos osmóticos en los eritrocitos Fig. 5-9
Presión de turgor en las células vegetales cytoplasm central vacuole When water is plentiful, it fills the central vacuole, pushes the cytoplasm against the cell wall, and helps maintain the cell's shape Water pressure supports the leaves of this impatiens plant (a) Turgor pressure provides support cell wall plasma membrane When water is scarce, the central vacuole shrinks and the cell wall is unsupported (b) Loss of turgor pressure causes the plant to wilt Deprived of the support from water, the plant wilts Fig. 5-10
Author Animation: Active Transport
Transporteactivo (extracellular fluid) 1 The transport 2 Energy from ATP 3 The protein protein binds both changes the shape of the releases the ion and ATP and Ca 2+ transport protein and moves the ion across the membrane the remnants of ATP (ADP and P) and closes recognition site ATP ATP binding site ATP ADP P Ca 2+ (cytoplasm) Fig. 5-11
Tipos de transporte activo
Cotransporte activo simpuerto y antipuerto
Pinocitosis (extracellular fluid) 1 2 3 (cytoplasm) vesicle containing extracellular fluid 1 A dimple forms in the plasma membrane, which deepens 2 and surrounds the extracellular fluid. The 3membrane encloses the extracellular fluid, forming a vesicle. (a) Pinocytosis 1 extracellular fluid 2 cytoplasm 3 (b) TEM of pinocytosis Fig. 5-12
Endocitosismediadaporreceptores nutrient molecule (extracellular fluid) 1 Receptor proteins for specific molecules or complexes of molecules are localized at coated pit sites. receptor 1 2 The receptors bind the molecules and the membrane dimples inward. coated pit 2 3 4 3 The coated pit region of the membrane encloses the receptor-bound molecules. (cytoplasm) (a) Receptor-mediated endocytosis coated vesicle 4 A vesicle ("coated vesicle") containing the bound molecules is released into the cytoplasm. (extracellular fluid) extracellular particles bound to receptors coated vesicle 1 (cytoplasm) 2 3 4 protein coating coated pit plasma membrane (b) TEM of receptor-mediated endocytosis 0.1 micrometer Fig. 5-13
Fagocitosis Fig. 5-14
Exocitosis Fig. 5-15
Relaciónárea/volumen r r r distance to center (r) surface area (4πr 2 ) Volume (4/3πr 3 ) 1.0 2.0 4.0 12.6 50.3 201.1 4.2 33.5 268.1 area/volume 3.0 1.5 0.75 Fig. 5-16
Unionesintercelulares small intestine plasma membranes (edge view) protein filaments in the cytoplasm desmosome microvilli cells lining the small intestine (a) Desmosomes In desmosomes, protein filaments hold cells together plasma membranes (edge view) urinary bladder cells lining the bladder (b) Tight junctions In tight junctions, proteins seal cells together Fig. 5-17
Unionesintercelulares plasma membranes liver liver cells (a) Gap junctions In gap junctions, channel proteins connect the insides of adjacent cells root In plasmodesmata, membrane-lined channels connect the insides of adjacent cells plasma membranes cell walls root cells (b) Plasmodesmata Fig. 5-18