4 - Membrane Biogenesis

4 - Membrane Biogenesis - Lecture 3: Compartmental...

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Unformatted text preview: Lecture 3: Compartmental organization of eukaryotic cells and the biogenesis of membranes Figure 11-7 Molecular Biology of the Cell ( Garland Science 2008) Different energy sources can be used to pump molecules up their electrochemical gradient Figure 11-8 Molecular Biology of the Cell ( Garland Science 2008) Coupling active transport to the electro-chemical gradient of another molecule is a common mechanism. There are 2 types: There are 3 types of ATP-driven transporters: P-type (we will discuss next) F-type (rotary engines) ABC (largest family) Figure 11-14 Molecular Biology of the Cell ( Garland Science 2008) Example of an ATP-driven active transporter: The plasma membrane Na + K + pump ~10 mM ~150 mM ~150 mM ~5 mM electrogenic ! The sodium gradient maintained by the Na + K + pump plays key metabolic role maintenance of cellular pH, e.g. through Na + driven Cl- , HCO 3- exchanger uptake of sugars via Na +- driven symporters consumes ~1/3 rd of energy supply in typical cells! Figure 11-15 Molecular Biology of the Cell ( Garland Science 2008) How the pump works: Na triggers ATP-binding and phosphorylation, K+ triggers dephosphorylation to complete cycle our knowledge of how transporters and channels work has advanced enormously over the past decade, largely due to major advances in determining the precise 3- dimensional structure of these proteins in different stages of the transport cycle using X-ray crystallography. Eukaryotic cells have 1,000-10,000 greater volume than a bacterial cell (10-30 times longer). To deal with the huge increase in volume and biochemical complexity, eukaryotic cytoplasm is organized into distinct compartments Bacterial cells essentially have a single compartment in their cytoplasm where most of the reactions of life occur Figure 12-1 Molecular Biology of the Cell ( Garland Science 2008) A eukaryotic cell has many different compartments Table 12-1 Molecular Biology of the Cell ( Garland Science 2008) The cytosol accounts for 50% of the volume of cytoplasm. The nucleus is only ~6% Table 12-2 Molecular Biology of the Cell ( Garland Science 2008) Plasma membrane is only a tiny fraction of total Figure 12-2 Molecular Biology of the Cell ( Garland Science 2008) Cells are jammed-packed with compartments! As a general rule, compartments arise by growth and division of pre-existing compartments, and are not created de novo However, some compartments that are vesicular intermediates in transport processes are created from other membrane compartments Figure 12-6...
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4 - Membrane Biogenesis - Lecture 3: Compartmental...

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