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Biological membranes and transport - Coggle Diagram
- Biological membranes and transport
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Lipid Anchors
介紹
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– glycosylated phosphatidylinositol (GPI) • The lipid part can become part of the membrane. • The protein is now anchored to the membrane.
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– Some, such as GPI anchors are found only on the outer
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Membranes
What is?
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sheets • Composed of a variety of lipids and proteins • All cells have a cell membrane, which separates the
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that divide the internal space into compartments (i.e.,
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Electron Micrograph of Biological Membranes
Function
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– Selective export of waste and toxins (e.g. antibiotics) • Retain metabolites and ions within the cell • Sense external signals and transmit information into the
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– separate energy-producing reactions from energy-consuming ones – keep proteolytic enzymes away from important cellular proteins
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Common features
Sheet-like flexible structure, 30–100 Å (3–10 nm) thick • Main structure is composed of two leaflets of lipids (bilayer)
– with the exception of archaebacteria: monolayer of bifunctional lipids • Form spontaneously in aqueous solution and are stabilized
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by noncovalent forces, especially hydrophobic effect • Protein molecules span the lipid bilayer • Asymmetric
– Some lipids are found more commonly “inside.” – Some lipids are found more commonly “outside.” – Carbohydrate moieties are attached on the outer leaflet. – They can be electrically polarized.
Fluid Mosaic Model流體鑲嵌模型
Proposed in 1972 by Singer and Nicholson (UCSD) • Lipids form a viscous, two-dimensional solvent into which
proteins are inserted and integrated more or less deeply. • Proteins can either be embedded in or associated with the
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– Integral proteins are firmly associated with the membrane, often
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The Composition
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- type of phospholipid varies
- abundance and type of sterols varies
- lack of sterols in prokaryotes
- cholesterol predominant in the plasma membrane, virtually
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Membrane Composition Is Highly Variable in Different Organisms p.14
不對稱asymmetry p.16
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Membrane Phases
Depending on their composition and the temperature,
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– liquid-ordered state (i.e., “gel phase”): individual
molecules do not move around – liquid-disordered state (i.e., “fluid phase”):
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• Heating causes phase transition from the gel to fluid. • Under physiological conditions, membranes are more
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