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Liposomes, Micelles, Membranes Liposomes, Micelles, Membranes Architectures of phospholipids Membrane proteins Biophysics Course held at Physics Department, University of Cagliari, Italy. Academic Year: 2016/2017. Dr. Attilio Vittorio Vargiu PLEASE NOTE! This material is meant just as a guide, it does not substitute the books suggested for the Course. 1 From molecules to polymers Structures assembled through molecular bricks • Polimers – Polynucleotides Nucleic Acids (RNA, DNA) – Polipeptides Proteins • Micelles, Liposomes, Membranes • Hybrid structures Ribosomes, Peptidoglycans Biophysics Course held at Physics Department, University of Cagliari, Italy. Academic Year: 2016/2017. Dr. Attilio Vittorio Vargiu PLEASE NOTE! This material is meant just as a guide, it does not substitute the books suggested for the Course. 2 From molecules to polymers Structures assembled through molecular bricks • Polimers – Polynucleotides Nucleic Acids (RNA, DNA) – Polipeptides Proteins • Micelles, Liposomes, Membranes • Hybrid structures Ribosomes, Peptidoglycans Biophysics Course held at Physics Department, University of Cagliari, Italy. Academic Year: 2016/2017. Dr. Attilio Vittorio Vargiu PLEASE NOTE! This material is meant just as a guide, it does not substitute the books suggested for the Course. 3 Architectures of amphipathic lipids Amphipathic nature of phospholipids leads to two major architectures in polar (aqueous) solvents: Biophysics Course held at Physics Department, University of Cagliari, Italy. Academic Year: 2016/2017. Dr. Attilio Vittorio Vargiu PLEASE NOTE! This material is meant just as a guide, it does not substitute the books suggested for the Course. 4 Architectures of amphipathic lipids Amphipathic nature of phospholipids leads to two major architectures in polar (aqueous) solvents: Micelle • Micelles: one layer exposed to solvent Biophysics Course held at Physics Department, University of Cagliari, Italy. Academic Year: 2016/2017. Dr. Attilio Vittorio Vargiu PLEASE NOTE! This material is meant just as a guide, it does not substitute the books suggested for the Course. 5 Architectures of amphipathic lipids Liposome/Vesicle Amphipathic nature of phospholipids leads to two major architectures in polar (aqueous) solvents: • Micelles: one layer exposed to solvent • Membranes (also vesicles/liposomes): two faces – leaflets – exposed to solvent Bilayer membrane Biophysics Course held at Physics Department, University of Cagliari, Italy. Academic Year: 2016/2017. Dr. Attilio Vittorio Vargiu PLEASE NOTE! This material is meant just as a guide, it does not substitute the books suggested for the Course. 6 Micelles or membranes? • Most phospho-/glyco-lipids prefer bilayer than micelle architectures. Why? • Bulkiness of two fatty acid chains does not allow fit of hydrophobic tails to interior of micelle. • Fatty acids’ salts (e.g. soaps) containing only one chain readily form micelles. • Other phases, such as hexagonal (HII), cubic, and more complex also found. Biophysics Course held at Physics Department, University of Cagliari, Italy. Academic Year: 2016/2017. Dr. Attilio Vittorio Vargiu PLEASE NOTE! This material is meant just as a guide, it does not substitute the books suggested for the Course. 7 Micelles or membranes? • Most phospho-/glyco-lipids prefer bilayer than micelle architectures. Why? • Bulkiness of two fatty acid chains does not allow fit of hydrophobic tails to interior of micelle. • Fatty acids’ salts (e.g. soaps) containing only one chain readily form micelles. • Other phases,• suchMicelles as hexagonal limited in (H size,II), cubic, less thanand more ~20 complexnm. also found. • Bilayers can be macroscopic, up to ~106 nm. • …a reason for preference of latter in living organisms. Biophysics Course held at Physics Department, University of Cagliari, Italy. Academic Year: 2016/2017. Dr. Attilio Vittorio Vargiu PLEASE NOTE! This material is meant just as a guide, it does not substitute the books suggested for the Course. 8 Micelles or membranes? All of these phases are formed by different natural lipids under variable conditions Biophysics Course held at Physics Department, University of Cagliari, Italy. Academic Year: 2016/2017. Dr. Attilio Vittorio Vargiu PLEASE NOTE! This material is meant just as a guide, it does not substitute the books suggested for the Course. 9 Self-assembly of amphipathic lipids • Lipid bilayers (as well as micelles) form spontaneously in polar solvents (self-assembly). • Process mainly driven by entropy and by optimization of hydrophobic interactions among lipid tails. • Electrostatic and H-bonds interactions between polar heads and solvents contribute to stabilization. • Membranes are cooperative structures: – Tend to be extensive. – Tend to close on themselves (forming vesicles/compartments) as to avoid hydrophobic edges exposed to solvent. – Are self-sealing (holes thermodynamically unstable). Biophysics Course held at Physics Department, University of Cagliari, Italy. Academic Year: 2016/2017. Dr. Attilio Vittorio Vargiu PLEASE NOTE! This material is meant just as a guide, it does not substitute the books suggested for the Course. 10 Self-assembly of micelles Biophysics Course held at Physics Department, University of Cagliari, Italy. Academic Year: 2016/2017. Dr. Attilio Vittorio Vargiu PLEASE NOTE! This material is meant just as a guide, it does not substitute the books suggested for the Course. 11 Self-assembly of bilayers Biophysics Course held at Physics Department, University of Cagliari, Italy. Academic Year: 2016/2017. Dr. Attilio Vittorio Vargiu PLEASE NOTE! This material is meant just as a guide, it does not substitute the books suggested for the Course. 12 Key features of membranes Common features to all membranes • Sheet-like structures 5-10 nm thick (3-4 nm hydrophobic core). • Contain lipids (phospho-, glyco-, sphingo-lipids, sterols), proteins and carbohydrates. • Amphipathic lipids self-assemble in aqueous environment, held together by cooperative non-covalent interactions, and act as a barrier to flux of polar molecules. • Asymmetric: inner and outer leaflet (faces) always differ. • 2D solutions of oriented proteins and lipids: in general can translate into membrane plane, but rotations across membrane infrequent. • Most electrically polarized, with negative potential inside (typically ~ -60 mV). Different membranes have their peculiarities (e.g. plasma membrane is peculiar with respect to membranes of organelles) and associated proteins can be also highly specific of that membrane. Biophysics Course held at Physics Department, University of Cagliari, Italy. Academic Year: 2016/2017. Dr. Attilio Vittorio Vargiu PLEASE NOTE! This material is meant just as a guide, it does not substitute the books suggested for the Course. 13 Composition of membranes Asymmetry key feature of biological membranes (e.g. plasma) Biophysics Course held at Physics Department, University of Cagliari, Italy. Academic Year: 2016/2017. Dr. Attilio Vittorio Vargiu PLEASE NOTE! This material is meant just as a guide, it does not substitute the books suggested for the Course. 14 Composition of membranes Highly variable lipids mixtures, depending on function. Biophysics Course held at Physics Department, University of Cagliari, Italy. Academic Year: 2016/2017. Dr. Attilio Vittorio Vargiu PLEASE NOTE! This material is meant just as a guide, it does not substitute the books suggested for the Course. 15 Composition of membranes Highly variable protein/lipid mass ratio (from 1:5 to 4:1) depending on role of specific membranes: • Myelin (membrane insulating certain nervous fibers) has low content of proteins (15-30%) because pure lipids are good insulators. • Plasma membranes contain ~50% of proteins (pumps, channels, receptors, enzymes). • Mitochondrial and chloroplasts internal membranes transduce energy, need proteins (~75% of proteins). Type of proteins also vary with specific function of membrane. Biophysics Course held at Physics Department, University of Cagliari, Italy. Academic Year: 2016/2017. Dr. Attilio Vittorio Vargiu PLEASE NOTE! This material is meant just as a guide, it does not substitute the books suggested for the Course. 16 Functions of biological membranes Biological membranes define inside vs. outside of any cell and of organelles in eukaryotic cells • Prevent leaking of intracellular material and penetration of unwanted compounds. • Selective permeability through membrane proteins (pumps and channels) floating in lipids sea. • Additional functions associated to other membrane proteins: energy storage, information transduction, receptor functions, enzymatic activity, etc… Biophysics Course held at Physics Department, University of Cagliari, Italy. Academic Year: 2016/2017. Dr. Attilio Vittorio Vargiu PLEASE NOTE! This material is meant just as a guide, it does not substitute the books suggested for the Course. 17 Plasma membranes in some cells • Plasma membranes present in all kinds of cells. • Differ in Gram- and Gram+ bacteria. Biophysics Course held at Physics Department, University of Cagliari, Italy. Academic Year: 2016/2017. Dr. Attilio Vittorio Vargiu PLEASE NOTE! This material is meant just as a guide, it does not substitute the books suggested for the Course. 18 Plasma membranes in some cells • Gram+ and archaea have one membrane surrounded by cell wall. • Gram- two membranes separated by periplasm (contains proteins, peptides, and carbohydrates) lying in between. • Outer membrane quite permeable to small molecules owing to presence of porins. Biophysics Course held at Physics Department,
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