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MEMBRANE TRANSPORT BIOT 309 2012

MEMBRANE TRANSPORT BIOT 309 2012. Chapter 3, Kim and Gadd. Cytoplasmic Membrane Function. Controls passage of substances into and out of the cell; selectively permeable Functions in energy storage Harvests light energy in photosynthetic prokaryotes.

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MEMBRANE TRANSPORT BIOT 309 2012

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  1. MEMBRANE TRANSPORTBIOT 309 2012 Chapter 3, Kim and Gadd

  2. Cytoplasmic Membrane Function • Controls passage of substances into and out of the cell; selectively permeable • Functions in energy storage • Harvests light energy in photosynthetic prokaryotes

  3. Control of SubstancesAcross Cytoplasmic Membrane • Occurs by passive or active processes • Naturally impermeable to most substances • Proteins allow substances to cross membrane • Maintains a concentration gradient and electrical gradient • Chemicals concentrated on one side of the membrane or the other • Voltage exists across the membrane

  4. Passive Processes of Transport • Simple diffusion: rate depends simply on solute concentration • Facilitated diffusion: rate directly proportional to fraction of carrier proteins associated with solute

  5. Effects of Solutions on Organisms Figure 3.18

  6. Porins – Facilitated Diffusion • move many substances • General < 650 Daltons (Da) • Specialized > 650 Da • Located in OM in G (-)

  7. Active Processes of Transport • ELECTROCHEMICAL energy • H+ or another cation • Precursor/product antiporter in lactic acid bacteria

  8. AGAINST [] GRADIENT NO YES YES

  9. Active Processes of Transport*** • ATP-dependent transport: ATP-binding cassette (ABC) pathway • transport against a concentration gradient coupled to the hydrolysis of ATP • Essential in prokaryotes and eukaryotes • Uses binding proteins (high-affinity) • Part of superfamily, i.e., many similar proteins across many species • Histidine and maltose

  10. ABC 3D structure from x-ray crystallography α helix β-pleated sheet 2 subunits

  11. Structural Changes

  12. Passive transport requires no energy from the cell. Examples include the diffusion of oxygen and carbon dioxide, osmosis of water, and facilitated diffusion.

  13. Active transport requires the cell to spend energy, usually in the form of ATP. Examples include transport of large molecules (non-lipid soluble) and the sodium-potassium pump.

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