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BIOLOGICAL MEMBRANES

BIOLOGICAL MEMBRANES. Associate Professor Dr. Wipa Suginta School of Biochemistry, Institute of Science. References Lehninger Principles of Biochemistry by David L. Nelson, Michael M. Cox. Biochemistry by Jeremy M. Berg, John L. Tymoczko , Lubert Stryer .

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BIOLOGICAL MEMBRANES

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  1. BIOLOGICAL MEMBRANES Associate Professor Dr. Wipa Suginta School of Biochemistry, Institute of Science • References • Lehninger Principles of Biochemistry by David L. Nelson, Michael M. Cox. • Biochemistry by Jeremy M. Berg, John L. Tymoczko, LubertStryer. • Biochemistry by Donald Voet, Judith G. Voet. Membranes_WipaSuginta_2/2556

  2. Overview of cellular membranes The boundaries of cells are formed by plasma membranes Plasma membranes prevent molecules inside the cell fromleaking out and unwantedmolecules from diffusing in. Red-blood-cell plasma membranes Courtesy of Dr. Vincent Marches Membranes_WipaSuginta_2/2556

  3. Membrane permeabilityLipid bilayers are highly impermeable to ions and most polar molecules. Membranes_WipaSuginta_2/2556

  4. Isolation of cellular membranes by ‘differential centrifugation’ Membranes_WipaSuginta_2/2556

  5. Isolation of cellular membranes by ‘density gradient centrifugation’ Membranes_WipaSuginta_2/2556

  6. Lipid vesicles can be formed from phospholipids Membranes_WipaSuginta_2/2556

  7. Liposome for drug delivery Membranes_WipaSuginta_2/2556

  8. Common features of biological membranes Membranes are sheet-like structure. The thickness is between 60 – 100 Å (6-10 nm). Membrane lipid bilayers are barriers to the polar molecules. Membranes provide selective permeability around the cell. Specific proteins mediates distinct functions, such as pumps, channels, receptors, energy transducers, and enzymes. Membranes are non-covalent assemblies. Membranes are asymetric and fluidic. Most cell membranes are electrically polarized. For example, the intracellular face has negative potential of ~60 mV. Membrane potentials play a key role in transport, energy conversion, and excitability. Membranes_WipaSuginta_2/2556

  9. Membrane transporters Membranes_WipaSuginta_2/2556

  10. Energy transducer on the outer membrane of mitochondria ATP synthase (EC 3.6.3.14) is an important enzyme that provides energy for the cell to use through the synthesis of adenosine triphosphate (ATP). ATP is the most commonly used "energy currency" of cells from most organisms. ATP synthase consists of 2 regions • The FO portion is within the membrane. • The F1 portion of the ATP synthase is above the membrane, inside the matrix of the mitochondria. Membranes_WipaSuginta_2/2556

  11. Photosynthesis on the thylakoid membranes of plant cells Photosynthesis is a process used by plants and other autotrophic organisms to convert light energy, normally from the sun, into chemical energy that can be used to fuel the organisms' activities. Carbohydrates, such as sugars, are synthesized from carbon dioxide during the process. In plants, light-dependent reactions occur in the thylakoid membranes of the chloroplasts and use light energy to synthesize ATP and NADPH. In the light-independent (or "dark") reactions, the enzyme RuBisCO captures CO2 from the atmosphere and in a process that requires the newly formed NADPH, called the Calvin-Benson Cycle, releases three-carbon sugars, which are later combined to form sucrose and starch. Membranes_WipaSuginta_2/2556

  12. Membrane receptors The insulin receptor is embedded in the cell membranes of muscle, fat cells and certain types of other cells. Its function is to facilitate their uptake of glucose from the blood stream through special glucose transport proteins that are normally present inside the cell in an inactive form. When the insulin molecule binds to the alpha subunits of the receptor, it triggers a chain reaction within the cytosol that activates GLUT4 and causes it to be translocated and inserted into the cell membrane. Membranes_WipaSuginta_2/2556

  13. Chemical composition of cellular membranes • Three common types of membrane lipids • Phospholipids • Glycolipids • Cholesterols • Membrane consists mainly of lipids and • proteins (mass ratio ranging from 1:4 to • 4:1). • Membranes also contain carbohydrates • that are linked to lipids or proteins and • cholesterols. Membranes_WipaSuginta_2/2556

  14. Asymmetry of carbohydrates in plasma membranes Carbohydrates – Total asymmetry Membranes_WipaSuginta_2/2556

  15. Asymmetry of lipids in plasma membranes Lipids – partial asymmetry Membranes_WipaSuginta_2/2556

  16. Different membranes have different lipid compositions Membranes_WipaSuginta_2/2556

  17. Phospholipids are major membrane lipids Membranes_WipaSuginta_2/2556

  18. Effect of temperature on membrane fluidity Types of phospholipids that affect membrane fluidity Membranes_WipaSuginta_2/2556

  19. Bleaching experiments to demonstrate membrane movement Fluorescence Loss in Photobleaching (FLIP) Membranes_WipaSuginta_2/2556

  20. Immunological experiments that demonstrate lateral movement of lipids in membranes Membranes_WipaSuginta_2/2556

  21. Movement of phospholipids in a bilayer Membranes_WipaSuginta_2/2556

  22. Cholesterol in plasma membranes Membranes_WipaSuginta_2/2556

  23. Asymmetry of proteins in plasma membranes Proteins – Total asymmetry Association of proteins with the cell membranes Membranes_WipaSuginta_2/2556

  24. Plasma membrane proteins have a variety of functions Membranes_WipaSuginta_2/2556

  25. Membrane proteins are covalently attached to lipids by various acyl groups Membranes_WipaSuginta_2/2556

  26. Transport of proteins to endoplasmic reticulum (ER) Proteins incorporated into the plasma membrane, enzymes in lysosomes and proteins secreted to the outside of the cell are synthesized in ribosomes attached to the ER membrane. Membranes_WipaSuginta_2/2556 See movie: http://csls-text.c.u-tokyo.ac.jp/flash/0544_1.html

  27. Transport vesicles transport the membrane components and secretory proteins. The destination of a transport vesicle is determined by the type of SNARE protein. When the transport vesicle is fused with the plasma membrane, proteins on the membrane stay on the cell surface, while those inside the transport vesicle are released to the outside of the cell. Membranes_WipaSuginta_2/2556

  28. Topology prediction of integral membrane proteins Hydropathy plot of glycophorin Membranes_WipaSuginta_2/2556

  29. Membranes_WipaSuginta_2/2556

  30. Hydropathy plot of bacteriorhodopsin Membranes_WipaSuginta_2/2556

  31. Channel proteins can be formed from beta-strands Structure of bacterial porin Membranes_WipaSuginta_2/2556

  32. Visualization of membrane proteins by atomic force microscopy (AFM) Membranes_WipaSuginta_2/2556

  33. Solubilization of membrane proteins by detergents Membranes_WipaSuginta_2/2556

  34. Properties of detergents Membranes_WipaSuginta_2/2556

  35. A common experimental system for studying the functions of transport proteins is liposomes containing a purified transport protein. Membranes_WipaSuginta_2/2556

  36. Liposome swelling assay is the technique to study permeation of molecules across membranes Membranes_WipaSuginta_2/2556

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