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Transcript
Membranes • Everything in life is variable – Chaotic • Membranes organize the chaos of cellular metabolism – E.g. houses & stores with doors & gates – E.g. streets organize traffic • Selectively permeable – Allows some things in & blocks some things • Plasma membrane (cell) – Takes up what cell needs & takes out the trash • Thin, requires EM at 200,000x • 3 zones – Construction of Phospolipids Phospholipid • Polar, hydrophilic head – Phosphate group – React and interact with the environment • Non-polar, hydrophobic tail – Two-tailed fatty acid • Relation w/ water = Phospholipid Bi-layer – Non-polar, hydrophobic molecules move more freely through the membrane (soluble in lipids) • E.g. vessicles and vacuoles transporting packages throughout membrane system • E.g. soap to clean (breakdown) grease – Polar molecules & ions not soluble • Membrane = Fluid mosaic of phospholipids and proteins • Mosaic – Made up of many small pieces • Mosaic = diverse proteins embedded in phospholipids • Fluid = proteins can drift laterally within bi-layer • Cholesterol – helps stabilize at body temperature & maintains fluidity at lowered temperatures • Glycolipids & glycoprotiens – Carbohydrate ID tags • E.g. immune system recognizes good cells from bacterial cells • E.g. embryonic development – cells differentiate (tissues & organs) • Proteins – do most of the work Membrane Proteins • Very diverse – E.g. >50 different proteins in plasma membrane of human blood cells • Enzymes – catalyze molecule assembly (e.g. modify by increasing rate) • Receptors – messengers from other cells (e.g. hormones) • Transport – allows large molecules to pass Passive Transport = diffusion • Diffusion = natural tendency of particles to spread evenly (from high concentration to low concentration) to reach balance • No energy required • Many smaller molecules simultaneously • E.g. O2 and CO2 move in & out of rbc’s Facilitated Diffusion • Size or polarity prevents diffusion? • Protein creates a channel or pore for passage – E.g. sugars, amino acids, ions, & water • Down concentration gradient (high conc. to low conc.) • Passive transport – No energy required Active Transport • Spends energy to push solutes against conc. gradient • Passive transport down a gradient is “as easy as falling in a hole” • But, how do you climb back up/out? • Use the notches/cracks/crevices, but takes energy - ATP Transport of LARGE molecules • Exocytosis – transport out of cell – Vesicle (membrane package) fuses with plasma membrane, opens, releases outside – E.g. salty tears from tear glands • Endocytosis – reverse of exocytosis – bringing in macromolecules from outside of plasma membrane – Pinching of membrane to form vesicle • Phagocytosis – cellular eating – Engulfs food molecules forming a vacuole, fuses with lysosomes for digestion • E.g. Amoeba • Pinocytosis – cellular drinking – Vesicles of non-specific liquid • Receptor mediated endocytosis – Pit forms in plasma membrane that is lined with specific receptors, pinches closed, releases molecules inside cytoplasm