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Membranes

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)

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Membranes

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  1. 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

  2. Thin, requires EM at 200,000x • 3 zones • Construction of Phospolipids

  3. Polar, hydrophilic head Phosphate group React and interact with the environment Non-polar, hydrophobic tail Two-tailed fatty acid Phospholipid

  4. 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

  5. Membrane = Fluid mosaic of phospholipids and proteins

  6. Mosaic Made up of many small pieces

  7. Mosaic = diverse proteins embedded in phospholipids • Fluid = proteins can drift laterally within bi-layer

  8. 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

  9. 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 Membrane Proteins

  10. Passive Transport = diffusion • Diffusion = natural tendency of particles to spread evenly (from high concentration to low concentration) to reach balance • No energy required

  11. Many smaller molecules simultaneously • E.g. O2 and CO2 move in & out of rbc’s

  12. 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 Facilitated Diffusion

  13. 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

  14. 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

  15. Endocytosis – reverse of exocytosis • bringing in macromolecules from outside of plasma membrane • Pinching of membrane to form vesicle

  16. 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

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