Phospholipid Bilayer Fibers of Extra- Cellular Matrix (ECM)

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Phospholipid Bilayer Fibers of Extra- Cellular Matrix (ECM)

Membrane Functions Cell Membranes 1. boundaries 6. Cell-cell Today’s Topics 2. Localize adhesion • Finish Cell Structure and Movement specific – Cytoskeleton functions – Motor Proteins • Membrane Structure – Fluid Mosaic 5. Cell-cell – How appropriate fluidity is maintained communication • Diffusion and Osmosis http://library.thinkquest.org/C004535/media/cell_membrane.gif 3. Transport Sept 19, 2011 4. Signal detection Figure 7.5 Phospholipid bilayer Fibers of extracellular matrix (ECM) Glyco- Carbohydrate protein Glycolipid Fig. 7-2 EXTRACELLULAR SIDE OF MEMBRANE WATER! Hydrophilic head! Cholesterol Microfilaments Peripheral of cytoskeleton proteins Hydrophobic Integral protein tail! CYTOPLASMIC SIDE OF MEMBRANE WATER! Membrane Structure: The Fluid Mosaic Model 1972 Singer & Nicholson • Proteins embedded and floating in a sea hydrophobic of phospholipids A B Phospholipid bilayer hydrophilic Protein and Lipid raft Figure 7.3 1 • Membrane proteins and lipids are Figure 7.6 synthesized in the ER and Golgi The Fluidity of Membranes apparatus 1 Transmembrane glycoproteins ER Secretory protein ~25% of known genes code for membrane Glycolipid Golgi 2 proteins apparatus Vesicle Most drugs target Lateral movement occurs Flip-flopping across the membrane membrane proteins !107 times per second. is rare (! once per month). 3 Plasma membrane: Cytoplasmic face 4 Extracellular face Transmembrane glycoprotein Secreted protein Membrane glycolipid Figure 7.10 Figure 7.7 Evidence for integral membrane proteins: Evidence for membrane fluidity? Freeze-Fracture Electron Microscopy Extracellular layer A cell is frozen and fractured with a knife. The fracture plane often follows the hydrophobic interior of a membrane, splitting the phospholipid bilayer into two separated layers. The membrane proteins go wholly with one of the layers. Mixed proteins Knife Proteins Mouse cell after 1 hour Human cell Hybrid cell Plasma membrane Cytoplasmic layer Illustrates: asymmetry of membrane components External Leaflet Cytoplasmic Leaflet Figure 7.4 Extracellular layer Cytoplasmic layer Fluid Viscous Unsaturated hydrocarbon Saturated hydro- Cholesterol tails with kinks Carbon tails Figure 7.5 (c) Cholesterol within the animal cell membrane (b) Membrane fluidity Figure 7.5 B 2 Figure 7.13a 1. Lipid bilayers are selectively permeable Simple Diffusion: • small,nonpolar • small uncharged, polar • larger uncharged, polar molecules • ions Net diffusion Net diffusion Equilibrium (a) Diffusion of one solute Decreasing Size – polarity - ions permeability Osmosis Low High [Solute]! [Solute]! H2O! Semi- permeable membrane More Less free free water water Osmosis! 3 .

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Membrane Structure Overview Pathology > Cellular Biology & Genetics > Cellular Biology & Genetics
Membrane Structure Overview Pathology > Cellular Biology & Genetics > Cellular Biology & Genetics PLASMA MEMBRANE • Phospholipid bilayer: bilayer that comprises mostly phospholipids • Fluid mosaic: mosaic of proteins embedded within a fluid phospholipid bilayer • Selectively permeable: some substances move through passively, others use proteins for transport MEMBRANE COMPONENTS • Phospholipids • Proteins • Cholesterol • Carbohydrates PHOSPHOLIPIDS • Amphipathic: hydrophilic head and hydrophobic fatty acid tails • Form liposomes in aqueous environment • Weak hydrophobic interactions = membrane fluidity • Saturated phospholipids: maximize hydrogens in fatty acid tails, no kinks • Unsaturated phospholipids: double bond produces kink, increases fluidity CHOLESTEROL • Temperature buffer • Moderate temperature: decreases fluidity, lessens lateral movement • Low temperature: increases fluidity, prevents solidification PROTEINS • Includes transmembrane proteins that span the bilayer (other types exist) • Proteins provide about half the mass of the membrane CARBOHYDRATES • Glycoproteins: branched carbohydrates covalently bound to proteins • Glycolipids: carbohydrates covalently bound to lipids (extracellular only) 1 / 5 CLINICAL CORRELATION: Blood types • Carbohydrates on surface of red blood cells must be compatible between donor & recipient in blood transfusion FUNCTIONS OF THE CELL MEMBRANE • Cell communication • Import and export of molecules • Cell growth • Cell motility Eukaryotes have internal membranes within the cell, prokaryotes do not.
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Cell Membrane
John Lenyo Corrina Perez Hazel Owens Cell Membrane http://micro.magnet.fsu.edu/cells/plasmamembrane/plasmamembrane.html • Cell membranes are composed of proteins and lipids. • Since they are made up of mostly lipids, only certain substances can move through. spmbiology403.blogspot.com •Phospholipids are the most abundant type of lipid found in the membrane. Phospholipids are made up of two layers, the outer and inner layers. The inside layer is made of hydrophobic fatty acid tails, while the outer layer is made up of hydrophilic polar heads that are pointed toward the water. academic.brooklyn.cuny.edu •Membrane structure relies on the tendency of fatty acid molecules to spread on the surface of water. • Membrane proteins (which take up half of the membrane) determine what gets into and leaves the cell. •Glycolipids are found on the outer part of the cell membrane. Single Chain vs. Phospholipid • Single chain lipids were assumed to be the first of those to form cell membranes with the more complex phospholipids evolving later • Phospholipids can be synthesized in an abiotic environment without enzymes now • Phosphoplipid bilayers now make up the plasma cell membranes that regulate movement into and out of prokaryotic and eukaryotic cells. Single chain lipid http://web.nestucca.k12.or.us/nvhs/staff/whitehead/homewor http://clincancerres.aacrjournals.org/content/11/5/2018/F1. k.htm expansion Types of Lipids • Today Plasma Membranes are made primarily of phospholipids • It is thought that early membranes may have been made of simpler fatty acids. http://exploringorigins.org/fattyacids.html Properties of Fatty Acids • They are Ampipathic, meaning that they have a hydrophobic (“water hating”) end and a hydrophilic (water loving”) end.
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Endoplasmic Reticulum-Plasma Membrane Contact Sites Integrate Sterol and Phospholipid Regulation
RESEARCH ARTICLE Endoplasmic reticulum-plasma membrane contact sites integrate sterol and phospholipid regulation Evan Quon1☯, Yves Y. Sere2☯, Neha Chauhan2, Jesper Johansen1, David P. Sullivan2, Jeremy S. Dittman2, William J. Rice3, Robin B. Chan4, Gilbert Di Paolo4,5, Christopher T. Beh1,6*, Anant K. Menon2* 1 Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada, 2 Department of Biochemistry, Weill Cornell Medical College, New York, New York, United States of a1111111111 America, 3 Simons Electron Microscopy Center at the New York Structural Biology Center, New York, New a1111111111 York, United States of America, 4 Department of Pathology and Cell Biology, Columbia University College of a1111111111 Physicians and Surgeons, New York, New York, United States of America, 5 Denali Therapeutics, South San a1111111111 Francisco, California, United States of America, 6 Centre for Cell Biology, Development, and Disease, Simon a1111111111 Fraser University, Burnaby, British Columbia, Canada ☯ These authors contributed equally to this work. * [email protected] (AKM); [email protected] (CTB) OPEN ACCESS Abstract Citation: Quon E, Sere YY, Chauhan N, Johansen J, Sullivan DP, Dittman JS, et al. (2018) Endoplasmic Tether proteins attach the endoplasmic reticulum (ER) to other cellular membranes, thereby reticulum-plasma membrane contact sites integrate sterol and phospholipid regulation. PLoS creating contact sites that are proposed to form platforms for regulating lipid homeostasis Biol 16(5): e2003864. https://doi.org/10.1371/ and facilitating non-vesicular lipid exchange. Sterols are synthesized in the ER and trans- journal.pbio.2003864 ported by non-vesicular mechanisms to the plasma membrane (PM), where they represent Academic Editor: Sandra Schmid, UT almost half of all PM lipids and contribute critically to the barrier function of the PM.
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An Overview of Lipid Membrane Models for Biophysical Studies
biomimetics Review Mimicking the Mammalian Plasma Membrane: An Overview of Lipid Membrane Models for Biophysical Studies Alessandra Luchini 1 and Giuseppe Vitiello 2,3,* 1 Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark; [email protected] 2 Department of Chemical, Materials and Production Engineering, University of Naples Federico II, Piazzale Tecchio 80, 80125 Naples, Italy 3 CSGI-Center for Colloid and Surface Science, via della Lastruccia 3, 50019 Sesto Fiorentino (Florence), Italy * Correspondence: [email protected] Abstract: Cell membranes are very complex biological systems including a large variety of lipids and proteins. Therefore, they are difficult to extract and directly investigate with biophysical methods. For many decades, the characterization of simpler biomimetic lipid membranes, which contain only a few lipid species, provided important physico-chemical information on the most abundant lipid species in cell membranes. These studies described physical and chemical properties that are most likely similar to those of real cell membranes. Indeed, biomimetic lipid membranes can be easily prepared in the lab and are compatible with multiple biophysical techniques. Lipid phase transitions, the bilayer structure, the impact of cholesterol on the structure and dynamics of lipid bilayers, and the selective recognition of target lipids by proteins, peptides, and drugs are all examples of the detailed information about cell membranes obtained by the investigation of biomimetic lipid membranes. This review focuses specifically on the advances that were achieved during the last decade in the field of biomimetic lipid membranes mimicking the mammalian plasma membrane. In particular, we provide a description of the most common types of lipid membrane models used for biophysical characterization, i.e., lipid membranes in solution and on surfaces, as well as recent examples of their Citation: Luchini, A.; Vitiello, G.
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Membrane Proteins Are Associated with the Membrane of a Cell Or Particular Organelle and Are Generally More Problematic to Purify Than Water-Soluble Proteins
Strategies for the Purification of Membrane Proteins Sinéad Marian Smith Department of Clinical Medicine, School of Medicine, Trinity College Dublin, Ireland. Email: [email protected] Abstract Although membrane proteins account for approximately 30 % of the coding regions of all sequenced genomes and play crucial roles in many fundamental cell processes, there are relatively few membranes with known 3D structure. This is likely due to technical challenges associated with membrane protein extraction, solubilization and purification. Membrane proteins are classified based on the level of interaction with membrane lipid bilayers, with peripheral membrane proteins associating non- covalently with the membrane, and integral membrane proteins associating more strongly by means of hydrophobic interactions. Generally speaking, peripheral membrane proteins can be purified by milder techniques than integral membrane proteins, whose extraction require phospholipid bilayer disruption by detergents. Here, important criteria for strategies of membrane protein purification are addressed, with a focus on the initial stages of membrane protein solublilization, where problems are most frequently are encountered. Protocols are outlined for the successful extraction of peripheral membrane proteins, solubilization of integral membrane proteins, and detergent removal which is important not only for retaining native protein stability and biological functions, but also for the efficiency of downstream purification techniques. Key Words: peripheral membrane protein, integral membrane protein, detergent, protein purification, protein solubilization. 1. Introduction Membrane proteins are associated with the membrane of a cell or particular organelle and are generally more problematic to purify than water-soluble proteins. Membrane proteins represent approximately 30 % of the open-reading frames of an organism’s genome (1-4), and play crucial roles in basic cell functions including signal transduction, energy production, nutrient uptake and cell-cell communication.
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Membrane Fluidity and the Perception of Environmental Signals In
Progress in Lipid Research 42 (2003) 527–543 www.elsevier.com/locate/plipres Review Membrane fluidity and the perception of environmental signals in cyanobacteria and plants Koji Mikami, Norio Murata* Department of Regulation Biology, National Institute for Basic Biology, Okazaki 444-8585, Japan Accepted 22 April 2003 Abstract Photosynthetic organisms, namely, plants and cyanobacteria, are directly exposed to changes in their environment and their survival depends on their ability to acclimate to such changes. Several lines of evi- dence suggest that temperature stress, such as unusually low or high temperatures, and osmotic stress might be perceived by plants and cyanobacteria via changes in the fluidity of their cell membranes. The availability of techniques for gene-targeted mutagenesis and gene transfer, as well as for the analysis of genomes and transcripts, has allowed us to examine and evaluate this hypothesis and its implications. In this review, we summarize recent studies of the regulation of gene expression by changes in the extent of unsaturation of fatty acids and membrane fluidity, and we present a discussion of the induction of gene expression by environmental stress and of sensors of environmental conditions and relationships between their activity and the fluidity of membranes in cyanobacteria and plants. # 2003 Elsevier Ltd. All rights reserved. Contents 1. Introduction ..........................................................................................................................................................
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Biological Membranes
14 Biological Membranes To understand the structure The fundamental unit of life is the cell. All living things are composed of Goal and composition of biological cells, be it a single cell in the case of many microorganisms or a highly membranes. organized ensemble of myriad cell types in the case of multicellular organisms. A defining feature of the cell is a membrane, the cytoplasmic Objectives membrane, that surrounds the cell and separates the inside of the cell, the After this chapter, you should be able to cytoplasm, from other cells and the extracellular milieu. Membranes also • distinguish between cis and trans surround specialized compartments inside of cells known as organelles. unsaturated fatty acids. Whereas cells are typically several microns (μm) in diameter (although • explain why phospholipids some cells can be much larger), the membrane is only about 10 nanometers spontaneously form lipid bilayers and (nm) thick. Yet, and as we will see in subsequent chapters, the membrane is sealed compartments. not simply an ultra-thin, pliable sheet that encases the cytoplasm. Rather, • describe membrane fluidity and how it membranes are dynamic structures that mediate many functions in the is affected by membrane composition life of the cell. In this chapter we examine the composition of membranes, and temperature. their assembly, the forces that stabilize them, and the chemical and physical • explain the role of cholesterol in properties that influence their function. buffering membrane fluidity. The preceding chapters have focused on two kinds of biological molecules, • explain how the polar backbone namely proteins and nucleic acids, that are important in the workings of a membrane protein can be accommodated in a bilayer.
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Review Questions Plasma Membrane
Review Questions Plasma Membrane 1. What is the function of the plasma membrane? The plasma membrane forms the outer boundary of all cells. Described as semi-permeable, the membrane regulates the passage of atoms and molecules in and out of the cell. All membrane-bound organelles are also built of plasma membrane. 2. Draw a phospholipid bilayer and label the polar heads and the non-polar tails. The plasma membrane is made of a phospholipid bilayer. Phospholipids have a glycerol backbone attached to two fatty acid chains (one is unsaturated) and one phosphate group. The phosphate has a negative charge. The rest of the lipid is nonpolar. Water is attracted to the phosphate group and repelled by the rest of the molecule, so a phospholipid has a dual nature: a hydrophilic region (“head”) and a hydrophobic region (“tails”). When placed in water, the phospholipids form a bilayer. The heads face outward and the tails stay inside. The bilayer is semi-permeable barrier. Some substances can freely cross the membrane whereas others are stopped. 3. Why is the plasma membrane described as a “fluid mosaic”? The plasma membrane is a fluid because the phospholipid molecule is unsaturated. At room temperature, this causes the bilayer to have the consistency of salad oil. The term “mosaic” refers to the variety of embedded transmembrane proteins scattered throughout the membrane. 4. Why is cholesterol an important component of animal cell membranes? Cholesterol is a component of the cell membranes of animals. Cholesterol makes the membrane less fluid and therefore more impermeable to biological molecules. In a sense, cholesterol creates a more solid membrane and a more restrictive membrane.
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ER–Mitochondria Contact Sites Reporters: Strengths and Weaknesses of the Available Approaches
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Factors Influencing the Membrane Fluidity and the Impact on Production of Lactic Acid Bacteria Starters
Applied Microbiology and Biotechnology (2019) 103:6867–6883 https://doi.org/10.1007/s00253-019-10002-1 MINI-REVIEW Factors influencing the membrane fluidity and the impact on production of lactic acid bacteria starters Fernanda Fonseca1 & Caroline Pénicaud 1 & E. Elizabeth Tymczyszyn2 & Andrea Gómez-Zavaglia3 & Stéphanie Passot1 Received: 19 April 2019 /Revised: 25 June 2019 /Accepted: 27 June 2019 /Published online: 12 July 2019 # Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract Production of lactic acid bacteria starters for manufacturing food, probiotic, and chemical products requires the application of successive steps: fermentation, concentration, stabilization, and storage. Despite process optimization, losses of bacterial viability and functional activities are observed after stabilization and storage steps due to cell exposure to environmental stresses (thermal, osmotic, mechanical, and oxidative). Bacterial membrane is the primary target for injury and its damage is highly dependent on its physical properties and lipid organization. Membrane fluidity is a key property for maintaining cell functionality, and depends on lipid composition and cell environment. Extensive evidence has been reported on changes in membrane fatty acyl chains when modifying fermentation conditions. However, a deep characterization of membrane physical properties and their evolution following production processes is scarcely reported. Therefore, the aims of this mini-review are (i) to define the membrane fluidity and the methods used to assess it and (ii) to summarize the effect of environmental conditions on membrane fluidity and the resulting impact on the resistance of lactic acid bacteria to the stabilization processes. This will make it possible to highlight existing gaps of knowledge and opens up novel approaches for future investigations.
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Current Research in Phospholipids and Their Use in Drug Delivery
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A. Membrane Functions Biological Membranes Are Composed Of… Membrane Lipid Protein
A. Membrane Functions Biological Membranes are composed of… Membrane Lipid Protein Myelin Sheath 80% 20% Plasma Membrane 50% 50% Mitochondrial 25% 75% Inner Membrane Fig. 5.12: Phospholipids Hydrophilic head 2 Hydrophobic tails Phospholipds are amphipathic molecules (contain both hydrophilic and hydrophobic parts) Phospholipids form Membrane Bilayers Bilayer consisting of two inverted phospholipid layers (leaflets) Hydrophobic ~30 Å ~45 Å Interior (3 nm) (4.5 nm) Hydrophobic interior is an impermeable barrier to passage of hydrophilic molecules, but not to hydrophobic molecules Cholesterol has profound effects on membrane fluidity Fig 7.8: Membrane Fluidity (a) Phospholipid molecules move side-to-side within leaflet easily (lateral diffusion) but do not “flip-flop” across bilayer (transverse diffusion) (b) Phospholipids containing unsaturated acyl chains increase membrane fluidity by reducing packing efficiency (c) Cholesterol reduces membrane fluidity at normal temperatures (reduces phospholipid movement) At low temperatures it keeps membrane fluid (disrupts packing) Membrane Proteins can Move Laterally Within the Lipid Bilayer Membrane proteins labeled with different color fluorescent dyes Supports fluid-mosaic model of a dynamic membrane structure Three Types of Membrane Proteins 1. Integral membrane proteins (transmembrane proteins) Extracellular domain • span the bilayer • transmembrane domain has Transmembrane hydrophobic surface domain • cytosolic and extracellular Cytosolic domains have hydrophilic surfaces domain 2. Lipid-anchored membrane proteins - anchored via a covalently attached lipid 3. Peripheral membrane proteins - interact with hydrophilic lipid head groups or with integral membrane proteins How do proteins cross lipid bilayer membranes? δ- δ+ δ- δ+ Even if the R-groups are hydrophobic, the peptide bond atoms are hydrophilic (polar) and will want to form Hydrogen Bonds; there are no H-bond donors or acceptors in the middle of a lipid bilayer.
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