DOCSLIB.ORG

The Role of Lipid Fluidity in the Function of the Thylakoid

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Role of Lipid Fluidity in the Function of the Thylakoid ) The Role of Lipid Fluidity in the Function of the Thylakoid Membrane by Robert Curtis Ford Thesis submitted for the degree of Doctor of Philosophy in the University of London, and for the Diploma of Membership of the Imperial College of Science and Technology. 1 ABSTRACT A fluorescence method for estimating the fluidity of the thyla- koid membrane was developed and compared with other more establis- hed techniques using ESR spin-label probes. The fluorescence method was found to have several advantages over the ESR spin-labelling technique in that only small quantities of sample were required (equivalent to 20 micrograms Chi.) and information on both the rate of motion as well as the static order of the lipid acyl chains could be obtained. Under physiological conditions a highly fluid lipid environment was shown to exist in the thylakoid membrane for the probe DPH with a viscosity of 0.3 poise for wobbling motions within a restricted cone of half-angle 50°. Treatments causing a reduction in lipid fluidity were found to inhibit photosynthetic electron flow between Photosystem 2 and Photosystem 1 which are organized into separate regions of the thylakoid membrane. Reduction in the fluidity of the lipid matrix was also found to restrict salt-induced changes in chlorophyll fluorescence which have been associated with lateral protein movement. The lipid matrix in stromal lamellae fractions was found to be much less ordered (order parameter, 0.38) than the granal membrane fractions (order parameter, 0.61). The differences observed were interpreted in terms of the high protein:lipid ratios in the granal fractions (1.9:1) compared to the stromal lamellae (1.2:1), and the importance of the protein:lipid ratio in the ordering of the thyla- koid lipid matrix is discussed in detail. 2 Acknowledgements I would like to thank everyone who has given help and encourage- ment to me during the last three years, and in particular I would like to thank Prof. James Barber, ray supervisor, whose enthusiasm for the study of photosynthesis has proved highly infectious. Much of this work would not have been possible without the helpful and patient instruction of Dr. David Chapman who has introduced me to the techniques of lipid extraction and analysis. I would also like to acknowledge the help of Dr. Raymond Cox at Odense University in Denmark who provided facilities and expertise for the measurement of the ESR spectra of spin-labels. Many others have contributed to this work by their constructive criticism and discussion of ideas and experiments, and in particu- lar I would like to thank Drs. Fred Chow, Yasusi Yamamoto, Paul Millner, Lars Olsen, Alison Telfer, Barry Rubin and Nigel Packham. I also acknowledge the invaluable technical support of Kathy Wilson and John De-Felice. Special thanks in particular to Alice Leeming for her help and encouragement over the last few years, and for her diligent pruf reeding. Finally I would like to thank the Science Research Council and Standard Telecommunications Laboratories Ltd. for financial support for this work. 3 Contents List of Tables 7 List of Figures 8 Symbols and Abbreviations 12 1 Introduction 14 1.1 General Introduction 14 1.2 The Two Light Reactions 16 1.3 Light-Harvesting Mechanisms: The Photosystems 18 1.4 Structure of the Chloroplast 20 1.4.1 The Thylakoid Membrane 20 1.4.2 The Envelope Membrane 22 1.5 Organization of the Electron Transport Components 23 1.5.1 Inter-System Electron Transfer Components 27 1.5.1.1 Plas toquinone 27 1.5.1.2 Primary Acceptors From PS 2 28 1.5.1.3 The Cytochromes 30 1.5.1.4 Plastocyanin 32 1.5.2 Photosystem 1 Reaction Centre: P700 33 1.5.3 Reactions on the Reducing Side of PS1 34 1.5.4 Photosystem 2 Reaction Centre: P680 37 1.5.5 Reactions on the Oxidizing Side of PS2 37 1.6 The Production of ATP 40 1.7 Lipid Composition and Structure of the Thylakoid Membrane 43 1.7.1 The Use of EPR spin-labels 49 1.8 The Effect of Temperature 51 1.9 Other Experiments on Thylakoid Membrane Fluidity 52 1.10 Summary 57 4 2 Materials and Methods 59 2.1 Plant Material 59 2.2 Chloroplast Preparations 59 2.2.1 Preparation of Class 1 Intact Chloroplasts 60 2.2.2 Preparation of Class 2 Broken Chloroplasts 61 2.2.3 Determination of Chlorophyll 61 2.3 Preparation of Thylakoid Membrane Fractions 62 2.3.1 Incubation Media 62 2.3.2 Fractionation Procedure 63 2.4 Preparation of Cholesterol-Treated Thylakoid Membranes 64 2.4.1 Determination of Cholesterol 66 2.5 Isolation and Analysis of Chloroplast Lipids 67 2.5.1 Fatty-Acid Analysis 67 2.5.2 Isolation of Chloroplast Lipids 69 2.6 Preparation of Lipid Vesicles 70 2.6.1 Chloroplast Lipids 70 2.6.2 Other Lipids 70 2.6.3 Lipid Enrichment Experiments 71 2.7 Protein Analysis 71 2.8 Electron Transport Measurements 72 2.8.1 Steady-State Electron Transport 72 2.8.2 Flash-Induced Electron Transport 73 2.9 Chlorophyll Fluorescence Measurements 76 2.9.1 Salt-Induced Chlorophyll Fluorescence Changes 76 2.9.2 Modulated Chlorophyll Fluorescence 76 2.10 ESR Measurements: Spin Labels 78 2.10.1 Measurement of First-Derivative ESR Spectra 78 2.10.2 Calculation of Rotational Correlation Times 79 5 2.10.3 Calculation of Order Parameters 80 2.11 Fluorescence Polarization Measurements 85 2.11.1 Preparation of DPH-Labelled Membranes 85 2.11.2 Steady-State Fluorescence Polarization Measurements 86 2.12 Time-Resolved Fluorescence Measurements 88 3 Results 91 3.1 Lipid Fluidity Measurements 91 3.1.1 A Fluorescent Probe: DPH 91 3.1.1.1 Fluorescence Polarization Measurements with DPH 109 3.1.1.2 Steady-State Fluorescence Polarization Measurements 110 3.1.1.3 Time-Resolved Fluorescence Depolarization Measurements 113 3.1.2 ESR Spin-Label Probes 120 3.2 Lipid Fluidity and Function 130 3.2.1 Effect of Temperature 131 3.2.2 Effect of Cholesterol 133 3.2.3 Effect of Ageing on Lipid Fluidity 151 3.3 Lateral Heterogeneity in the Thylakoid Membrane 155 3.3.1 Characterization of the Thylakoid Membrane Fractions 156 3.3.2 Fluidity Measurements of Stromal and Granal Membranes 157 3.3.3 Composition of the Stromal and Granal Fractions 166 3.3.4 Lipid Fluidity and the Temperature Sensitivity of Photo- system2 170 4 Discussion 175 4.1 Comparisons With Other Biological Membranes 175 4.2 Distribution of the Probes 185 4.3 Possible Links Between Lipid Fluidity and Lateral Diffusion 187 4.4 The Effect of Lipid Fluidity on Electron Flow 191 6 4.5 Stromal and Granal Membrane Fractions 197 4.6 Future Studies 204 5 References 208 Appendix 1 235 Appendix 2 240 List of Tables 1. Effect of temperature on photosynthetic processes in higher plants. 53 2. Effect of temperature on photosynthetic processes in algae. 55 3. Fluorescence lifetimes of DPH in thylakoid systems. 101 4. Motional parameters of DPH in thylakoid membrane systems. 119 5. Spin-label to chlorophyll ratios and order parameters in thylakoid membranes. 130 6. Order parameters in soya lipid/cholesterol vesicles. 142 7. Order parameters in cholesterol-treated thylakoid membranes. 143 8. PS 1 and PS 2 activities in pea thylakoid fractions. 156 9. DPH fluoresence polarization in pea thylakoid fractions. 159 10. Motional parameters of DPH in pea thylakoid fractions. 160 11. Levels of protein, acyl lipid and chlorophyll in pea thylakoid fractions. 168 12. Proteintlipid ratios in pea thylakoid membrane fractions. 168 13. Fatty-acid composition of pea thylakoid membrane fractions. 169 14. Comparison of the steady-state fluorescence polarization values of DPH in various biological membranes. 176 15. Comparison of the (time-resolved) motional properties of DPH in various biological membranes. 177 7 List of Figures 1. Diagrammatic representation of the light reactions of photosyn- thesis. 24 2. Two-dimensional representations of a lipid bilayer in the gel and liquid-crystalline states. 45 3. Structures of the major thylakoid acyl lipids. 48 4. Flow diagram of the fractionation procedures adopted to isolate granal and stromal membrane fragments. 65 5. Block diagram of the single-beam flash spectrophotometer. 74 6. Block diagram of the apparatus used to measure modulated chloro- phyll fluorescence from intact leaves. 77 7. Diagrammatic representations of first-derivative ESR spectra of fast and slow moving spin-labels. 84 8. Corrected excitation and emission spectra of DPH in various environments. 93 9. Corrected excitation and emission spectra of DPH in thylakoid membranes and soya-phospholipid liposomes. 94 10. Chlorophyll fluorescence excitation and emission spectra in the presence and absence of DPH. 96 11. Effect of increasing DPH levels on chlorophyll fluorescence.98 12. Fluorescence decay of DPH in thylakoid membranes. 102 13. Fluorescence decays of DPH in stromal and granal membrane fractions. 103 14. Lifetimes of DPH fluorescence in lipid-enriched thylakoid membranes. 106 15. Time-course of entry of DPH into the thylakoid membrane. 108 8 16. Fluorescence polarization values of DPH during the time-course of entry into the thylakoid membrane. Ill 17. Wavelength-dependence of the steady-state fluorescence polarization values of DPH. 112 18. Wobbling-in-cone model for the motion of DPH within a lipid bilayer (a), and the actual anisotropy decay for the probe in thylakoid membrane (b). 117 19. Total and difference fluorescence decays of DPH in the thylakoid membrane. 121 20. Total and difference fluorescence decays of DPH in DGDG vesicles. 122 21. Structures of the spin-labels used in ESR measurements of thylakoid membrane fluidity.
Load more

Recommended publications
  • 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.
    [Show full text]
  • 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 ..........................................................................................................................................................
    [Show full text]
  • 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.
    [Show full text]
  • Interdependence Between Chloroplasts and Mitochondria in the Light and the Dark
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Biochimica et Biophysica Acta 1366 (1998) 235^255 Review Interdependence between chloroplasts and mitochondria in the light and the dark Marcel H.N. Hoefnagel a, Owen K. Atkin b, Joseph T. Wiskich a;* a Department of Botany, University of Adelaide, Adelaide, SA 5005, Australia b Research School for Biological Sciences, Australian National University, Canberra, ACT 0200, Australia Received 21 April 1998; revised 3 June 1998; accepted 10 June 1998 ß 1998 Elsevier Science B.V. All rights reserved. Keywords: Chloroplast; Chlororespiration; Excess reductant; Metabolite exchange; Mitochondrion; Photosynthesis; Respiration Contents 1. Introduction .......................................................... 236 2. Interactions between organelles depends on metabolite exchange . .................. 236 2.1. ATP exchange ..................................................... 236 2.2. Transport of reducing equivalents across membranes . ....................... 237 2.3. Exchange of carbon compounds ....................................... 238 3. Respiration in the light . ................................................. 239 3.1. Does respiration continue in the light? . .................................. 239 3.2. Substrates for the mitochondria in the light . ............................ 240 3.3. ATP supply in the light: chloroplasts versus mitochondria . .................. 240 3.4. Adenylate control of respiration in the light .
    [Show full text]
  • Calvin Cycle E
    Photosynthesis Photosynthesis is the process by which plants use sunlight (light energy) to produce glucose from carbon dioxide and water, with oxygen as a byproduct. This process occurs LIGHT STROMA in the chloroplasts in a plant cell and has DEPENDENT Cytochrome b f Reduced REACTIONS two stages – the light-dependent reactions 6 NADP NADP + 1. Light activation of and the light-independent reactions. H ATP synthase photocentres It all starts with the sunlight hitting e- PSII 2. Photolysis of water - + the fi rst photocentre (PSII). (P68 e PSI H e- (P 3. Electron transport e- ATP e- + 4. Pumping H into the + O H thylakoid space ADP + Pi H O + + H 5. Synthesis of ATP H 6. Reduction of NADP Photolysis THYLAKOID SPACE CO OXYGEN Thylakoid membrane GLUCOSE REDUCED NADP & ATP NADP REDUCED Glucose is used in respiration for energy. Glucose is converted to: 1. Cellulose for cell walls 2. Sucrose for transport 3. Starch for storage ADP + Pi & NADP + Pi ADP CHLOROPLAST CALVIN C LIGHT CO YCL E ( Six INDEPENDENT RuBisCO tu rn enzyme BON FIXAT s CAR ION to REACTIONS p ro d u c Calvin cycle e RuBP GP g l 1. Carbon fi xation u Ribulose bisphosphate Glycerate phosphate c o s e ) 2. Reduction P B 3. Regeneration of RuBP u R ATP F ADP + Pi O N ADP + Pi O R I ATP E T D A R Reduced NADP U E C N T E I O G NADP N E R GALP Glyceraldehyde phosphate Hexose Glucose LAMELLA THYLAKOIDS STROMA KEY TO SYMBOLS INNER CHLOROPLAST MEMBRANE Carbon atom: Electron transport: e- OUTER CHLOROPLAST MEMBRANE H+ movement: GLOSSARY ATP synthase: An enzyme that catalyses the Ferrodoxin: An electron carrier sitting just Light-dependent reactions: The fi rst stage Photosystem I (PSI): The second photosystem Plastoquinone: A molecule that is reduced Regeneration of RuBP: The third stage of Stroma: The aqueous solution that fi lls the synthesis of ATP from ADP and inorganic outside the thylakoid in the chloroplast of photosynthesis.
    [Show full text]
  • Bisphosphate Carboxylase/Oxygenase Activation in Tomato (Lycopersicon Esculentum Mil!.)
    Plant Physiol. (1995) 107: 585-591 The Effects of Chilling in the Light on Ribulose-1,5- Bisphosphate Carboxylase/Oxygenase Activation in Tomato (Lycopersicon esculentum Mil!.) George T. Byrd’, Donald R. Ort, and William 1. Ogren* Photosynthesis Research Unit, Agricultura1 Research Service, United States Department of Agriculture (G.T.B., D.R.O., W.L.O.), and Department of Plant Biology, University of lllinois at Urbana-Champaign (D.R.O., W.L.O.), Urbana, lllinois 61801 reduced leve1 of RuBP. The bisphosphatases are activated Photosynthesis rate, ribulose-l,5-bisphosphate carboxylase/oxy- by the Fd/thioredoxin system (Buchanan, 1980), which genase (Rubisco) activation state, and ribulose bisphosphate con- may be affected by the light-chilling regime. Thus, in to- centration were reduced after exposing tomato (Lycopersicon es- mato, chilling in the light appears to limit the capacity of culentum Mill.) plants to light at 4°C for 6 h. Analysis of lysed and leaves to regenerate RuBP, the substrate in photosynthetic reconstituted chloroplasts showed that activity of the thylakoid CO, fixation catalyzed by the enzyme Rubisco (EC membrane was inhibited and that Rubisco, Rubisco activase, and 4.1.1.39). other soluble factors were not affected. Leaf photosynthesis rates Rubisco activity also has been reported to be directly and the ability of chilled thylakoid membranes to promote Rubisco impaired during chilling in the light in short-term (Sas- activation recovered after 24 h at 25°C. Thylakoid membranes from control tomato plants were as effective as spinach thylakoids in senrath et al., 1990) and long-term (Briiggemann et al., activating spinach Rubisco in the presence of spinach Rubisco ac- 1992) experiments.
    [Show full text]
  • Molecular Biology of the Cell 6Th Edition
    753 CHAPTER Energy Conversion: Mitochondria and Chloroplasts 14 To maintain their high degree of organization in a universe that is constantly drift- IN THIS CHAPTER ing toward chaos, cells have a constant need for a plentiful supply of ATP, as we have explained in Chapter 2. In eukaryotic cells, most of the ATP that powers life THE MITOCHONDRION processes is produced by specialized, membrane-enclosed, energy-converting organelles. Tese are of two types. Mitochondria, which occur in virtually all cells THE PROTON PUMPS OF THE of animals, plants, and fungi, burn food molecules to produce ATP by oxidative ELECTRON-TRANSPORT CHAIN phosphorylation. Chloroplasts, which occur only in plants and green algae, har- ness solar energy to produce ATP by photosynthesis. In electron micrographs, the ATP PRODUCTION IN most striking features of both mitochondria and chloroplasts are their extensive MITOCHONDRIA internal membrane systems. Tese internal membranes contain sets of mem- brane protein complexes that work together to produce most of the cell’s ATP. In CHLOROPLASTS AND bacteria, simpler versions of essentially the same protein complexes produce ATP, PHOTOSYNTHESIS but they are located in the cell’s plasma membrane (Figure 14–1). Comparisons of DNA sequences indicate that the energy-converting organ- THE GENETIC SYSTEMS elles in present-day eukaryotes originated from prokaryotic cells that were endo- OF MITOCHONDRIA AND cytosed during the evolution of eukaryotes (discussed in Chapter 1). This explains CHLOROPLASTS why mitochondria and chloroplasts contain their own DNA, which still encodes a subset of their proteins. Over time, these organelles have lost most of their own genomes and become heavily dependent on proteins that are encoded by genes in the nucleus, synthesized in the cytosol, and then imported into the organelle.
    [Show full text]
  • Transport Proteins Enabling Plant Photorespiratory Metabolism
    plants Review Transport Proteins Enabling Plant Photorespiratory Metabolism Franziska Kuhnert, Urte Schlüter, Nicole Linka and Marion Eisenhut * Institute of Plant Biochemistry, Cluster of Excellence on Plant Science (CEPLAS), Heinrich Heine University Düsseldorf, Universitätsstrasse 1, 40225 Düsseldorf, Germany; [email protected] (F.K.); [email protected] (U.S.); [email protected] (N.L.) * Correspondence: [email protected]; Tel.: +49-211-8110467 Abstract: Photorespiration (PR) is a metabolic repair pathway that acts in oxygenic photosynthetic organisms to degrade a toxic product of oxygen fixation generated by the enzyme ribulose 1,5- bisphosphate carboxylase/oxygenase. Within the metabolic pathway, energy is consumed and carbon dioxide released. Consequently, PR is seen as a wasteful process making it a promising target for engineering to enhance plant productivity. Transport and channel proteins connect the organelles accomplishing the PR pathway—chloroplast, peroxisome, and mitochondrion—and thus enable efficient flux of PR metabolites. Although the pathway and the enzymes catalyzing the biochemical reactions have been the focus of research for the last several decades, the knowledge about transport proteins involved in PR is still limited. This review presents a timely state of knowledge with regard to metabolite channeling in PR and the participating proteins. The significance of transporters for implementation of synthetic bypasses to PR is highlighted. As an excursion, the physiological contribution of transport proteins that are involved in C4 metabolism is discussed. Keywords: photorespiration; photosynthesis; transport protein; plant; Rubisco; metabolite; synthetic bypass; C4 photosynthesis Citation: Kuhnert, F.; Schlüter, U.; Linka, N.; Eisenhut, M. Transport Proteins Enabling Plant Photorespiratory Metabolism. Plants 1. Introduction—The Photorespiratory Metabolism 2021, 10, 880.
    [Show full text]
  • Why Chloroplasts and Mitochondria Retain Their Own Genomes and Genetic Systems
    PAPER Why chloroplasts and mitochondria retain their own COLLOQUIUM genomes and genetic systems: Colocation for redox regulation of gene expression John F. Allen1 Research Department of Genetics, Evolution and Environment, University College London, London WC1E 6BT, United Kingdom Edited by Patrick J. Keeling, University of British Columbia, Vancouver, BC, Canada, and accepted by the Editorial Board April 26, 2015 (received for review January 1, 2015) Chloroplasts and mitochondria are subcellular bioenergetic organ- control. Fig. 2B illustrates the two possible pathways of synthesis elles with their own genomes and genetic systems. DNA replica- of each of the three token proteins, A, B, and C. Synthesis may tion and transmission to daughter organelles produces cytoplasmic begin with transcription of genes in the endosymbiont or of gene inheritance of characters associated with primary events in photo- copies acquired by the host. CoRR proposes that gene location synthesis and respiration. The prokaryotic ancestors of chloroplasts by itself has no structural or functional consequence for the and mitochondria were endosymbionts whose genes became mature form of any protein whereas natural selection never- copied to the genomes of their cellular hosts. These copies gave theless operates to determine which of the two copies is retained. Selection favors continuity of redox regulation of gene A, and rise to nuclear chromosomal genes that encode cytosolic proteins ’ and precursor proteins that are synthesized in the cytosol for import this regulation is sufficient to render the host s unregulated copy into the organelle into which the endosymbiont evolved. What redundant. In contrast, there is a selective advantage to location of genes B and C in the genome of the host (5), and thus it is the accounts for the retention of genes for the complete synthesis endosymbiont copies of B and C that become redundant and are within chloroplasts and mitochondria of a tiny minority of their lost.
    [Show full text]
  • Essential Cell Biology
    CHAPTER FOURTEEN 14 Energy Generation in Mitochondria and Chloroplasts The fundamental need to generate energy efficiently has had a pro- MITOCHONDRIA found influence on the history of life on Earth. Much of the structure, AND OXIDATIVE function, and evolution of cells and organisms can be related to their PHOSPHORYLATION need for energy. The earliest cells may have produced ATP by breaking down organic molecules, left by earlier geochemical processes, using some form of fermentation. Fermentation reactions occur in the cytosol MOLECULAR MECHANISMS of present-day cells. As discussed in Chapter 13, these reactions use the OF ELECTRON TRANSPORT energy derived from the partial oxidation of energy-rich food molecules AND PROTON PUMPING to form ATP, the chemical energy currency of cells. But very early in the history of life, a much more efficient method for gen- erating energy and synthesizing ATP appeared. This process is based on CHLOROPLASTS AND the transport of electrons along membranes. Billions of years later, it is so PHOTOSYNTHESIS central to the survival of life on Earth that we devote this entire chapter to it. As we shall see, this membrane-based mechanism is used by cells THE ORIGINS OF to acquire energy from a wide variety of sources: for example, it is central CHLOROPLASTS AND to the conversion of light energy into chemical-bond energy in photo- synthesis, and to the aerobic respiration that enables us to use oxygen MITOCHONDRIA to produce large amounts of ATP from food molecules. The mechanism we will describe first appeared in bacteria more than 3 billion years ago. The descendants of these pioneering cells crowd every corner and crev- ice of the land and the oceans with a wild menagerie of living forms, and they survive within eucaryotic cells in the form of chloroplasts and mitochondria.
    [Show full text]
  • Chapter 8 Application of Spin Labels to Membrane Bioenergetics
    Chapter 8 Application of Spin Labels To Membrane Bioenergetics (Photosynthetic Systems of Higher Plants) Alexander N. Tikhonov1 and Witold K. Subczynski2 1 Department of Biophysics, Faculty of Physics, M. V. Lomonosov Moscow State University, Moscow, 119899, Russia, 2National Biomedical EPR Center, Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226 Abstract: Following a brief overview of photosynthesis and the macro structure of chloroplasts, examples are presented of the use of nitroxyl spin labels and spin probes to investigate the processes of electron transport, proton transport, and oxygen transfer in chloroplasts. pH-sensitive nitroxyl radicals can be observed inside and outside thylakoids under various conditions, such as different levels of light. Oxygen consumption can be measured via the effect of oxygen on line width of the free radical. Lipid-soluble spin probes monitor changes in the biological membranes. 1. INTRODUCTION Photosynthesis is one of the most important biological processes. The great mass of experimental data obtained in numerous laboratories all over the world has given detailed information on the composition and molecular structure of the light-harvest complexes, electron transport chain (ETC) and ATP synthases in energy-transducing organelles of photosynthetic organisms — higher plants, cyanobacteria and photosynthetic bacteria (Lehninger et al., 1993; Blankenship, 2002). In this chapter, we will consider several aspects of the use of nitroxide radicals to investigate the processes of electron and proton transport, as well as the related processes of oxygen transfer, in chloroplasts — the energy-transducing organelles of the plant cell. Figures 1 and 2 depict a cross section of a chloroplast and a schematic of a chloroplast’s ETC.
    [Show full text]
  • 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.
    [Show full text]