DOCSLIB.ORG

Microbial Metabolism

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Microbial Metabolism Biol 3400 Tortora et al- Chap 5 Microbial Metabolism I. Metabolism • Metabolism is all of an organism's chemical processes (an emergent property that arises from interactions of molecules in the orderly environment of the cell) • Metabolism is very important for the management of cellular material and energy resources Metabolic reactions • Metabolic reactions are organized into pathways of enzyme controlled chemical reactions. • Cells need a supply of molecules and energy • Cells need to get rid of waste products Catabolic pathways • Break down complex molecules into simple molecules • Energy stored in complex molecules is made available to do work or transformed into readily usable chemical forms (i.e., ATP) • small molecules resulting from the catabolism of complex energy rich molecules may be used by the cell to build new molecules • e.g., cellular respiration Energy stored in compounds can be used to perform cellular work • mechanical - movement of cilia, chromosomes, organelles • transport - movement of substances across membranes • chemical - endergonic reactions Anabolic pathways • Use energy for the biosynthesis of complex molecules from simple molecules. • Energy is obtained from usable chemical forms of energy (i.e., ATP) produced during catabolic processes or from energy released during catabolic processes • e.g., synthesis of macromolecules Note: some pathways may function both catabolically and anabolically – these pathways are known as amphibolic pathways Review the Enzymes Section on your own (Pages 115 to 121) 1 Biol 3400 Tortora et al- Chap 5 II. Metabolic diversity among microorganisms • Life is based on organic molecules made of carbon skeletons • Oxygen and hydrogen are important elements of organic compounds • Electrons are needed i) for processes that provide energy (e.g., movement of electrons along energy transport chains and during oxidation reduction reactions) for cellular work and ii) to reduce molecules during biosynthesis • Molecules that serve as a source of carbon may also provide a source of oxygen and hydrogen • Microbes show an incredible ability to use organic molecules as carbon sources Organisms can be classified based on their sources of carbon, energy and electrons Carbon Source o Autotroph – CO2 is the sole or principal carbon source o Heterotroph – reduced, preformed, organic molecules from other organisms Energy Source o Phototrophs – Light o Chemotrophs – oxidation of organic or inorganic compounds Electron Source o Lithotrophs – reduced inorganic chemicals o Organotrophs – Organic molecules Major Nutritional Types of Microorganisms Carbon Energy Electron Examples Source source source 1. Photolithoautotrophy CO2 Light Inorganic Cyanobacteria, • aka - Photoautotrophs e- donor Purple sulfur bacteria 2. Photoorganoheterotrophy Organic Light Organic Purple nonsulfur • aka - Photoheterotrophs carbon but e- donor bacteria and Green CO2 may be nonsulfur bacteria used 3. Chemolithoautotrophy CO2 Inorganic Inorganic Sulfur oxidizing • aka - Chemoautotrophs chemicals e- donor bacteria, methanogens, nitrifying bacteria 4. Chemolithoheterotrophy Organic Inorganic Inorganic Some sulfur - carbon but chemicals e donor oxidizing bacteria CO2 may be Used 5. Chemoorganoheterotrophy Organic Organic Organic Most nonphotosynthetic • aka – Chemoheterotrophs carbon chemicals e- donor microbes including often the often the most pathogens, fungi, same as same as many protist and many C-source C-source archaea 2 Biol 3400 Tortora et al- Chap 5 III Heterotrophic (Chemoorganotrophic) Metabolism • Conversion of organic substrate molecules to end products by a metabolic pathway that releases sufficient energy for it to be coupled to the formation of ATP. • Chemoorganotrophs have three options for generating ATP from organic molecules; the electron acceptor used differentiates these processes: i) aerobic respiration, ii) anaerobic respiration and iii) fermentation i. Respiration • An external terminal electron acceptor is present and is not derived from the organic substrate • Involves the activity of an electron transport chain, proton motive force (PMF) is generated and ATP produced predominantly by oxidative phosphorylation a) Aerobic - O2 is the terminal electron acceptor. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + (ATP + Heat) - 2- b) Anaerobic - compounds other than O2 serve as electron acceptor (e.g., NO3 , SO4 , CO2, fumarate,…) *Some microbes can carry out both aerobic and anaerobic respiration – dependent upon the conditions ii. Fermentation • An external terminal electron acceptor is absent • Fermentation does not use an electron transport chain or the generation of a PMF • Fermentations are internally balanced oxidation-reduction reactions – i.e., the terminal electron acceptor is derived from the initial substrate or electron donor (e.g., glucose) • The terminal electron acceptor is required to balance redox reactions • Net result is energy production and an internally balanced redox reactions • ATP produced predominantly by substrate-level phosphorylation 3 Biol 3400 Tortora et al- Chap 5 A. Respiration 1. Glycolytic pathways • Breakdown of sugars to pyruvate and similar intermediates • Some production of ATP (substrate-level phosphorylation) and reducing power (reduced coenzymes; NADH) • Several pathways by which a cell can break down a sugar (sugars are the major substrates of catabolic energy releasing reactions used in heterotrophic metabolism). • Glycolytic pathways are typically anoxic processes that do not require oxygen • The end-product of glycolysis is commonly pyruvate COOH | C = O | CH3 Glycolytic pathways i). Embden-Meyerhof pathway (EMP) • Most common pathway - Central metabolic pathway for eukaryotic cells and many bacteria Net reaction 10 enzymatic steps Glucose + 2 ADP + 2 Pi + 2 NAD+→ 2 pyruvate + 2 ATP + 2 NADH + 2 H2O • ATP production - Substrate level phosphorylation • Phosphofructokinase is key enzyme in regulating this process, catalyzing the conversion of fructose – 6-P to fructose 1,6-bisphosphate ii). Entner-Doudoroff pathway • Mainly used by Gram negative soil bacteria and a few other Gram-negative bacteria as well as some Archaea • Lacks 6-phosphofructokinase (i.e., a key enzyme in Embden-Meyerhof pathway) Net reaction 9 enzymatic steps Glucose + ADP + Pi + NADP+ + NAD+ → 2 pyruvate + 1 ATP + NADPH + NADH + 1 H2O *NADPH is usually used in biosynthetic pathways 4 Biol 3400 Tortora et al- Chap 5 iii). Pentose Phosphate pathway • Can occur at the same time as the Embden-Meyerhof or the Entner-Doudoroff pathways • connects the metabolism of 6-C and 5-C sugars • Consumes 1 ATP • Products = reducing power (NADPH) and small molecules required for biosynthesis • 5-C sugars produced (e.g., ribose 5-phosphate; xylulose 5-phosphate) • Erythrose 4-phosphate is used to synthesize aromatic amino acids and vitamin B6 • Intermediates of the pathway may be fed into the EMP to produce ATP iv). Methylglyoxal pathway • Alternative to Embden-Meyerhof pathway during conditions of low phosphate availability • Consumes 2 ATP but produces pyruvate that can be used to generate ATP 2. Oxidation of pyruvate to 3 CO2. i) Initial Step + Pyruvate + NAD + CoA → Acetyl-CoA + NADH + CO2 • Three step process mediated by multienzyme pyruvate dehydrogenase complex • Acetyl CoA is a very unstable and reactive product. • Acetyl CoA feeds it's acetate → TCA cycle • Carbohydrates, fatty acids and amino acids may be converted into acetyl CoA during aerobic respiration ii) Tricarboxylic acid cycle (TCA cycle; also known as Citric acid cycle, Krebs cycle) • Discovered by Hans Krebs - 1930s • 8 steps involved in the TCA cycle • 2 C enter in a relatively reduced form – acetate and two different C leave in a completely oxidized form (CO2) • acetate joins the cycle by enzymatic addition to oxaloacetate (4 C) → formation of citrate • cyclical process resulting in the regeneration of oxaloacetate by the decomposition of citrate and evolution of 2 CO2 per acetate + • oxidation steps (transfer of electrons) of one acetate results in reduction of 3 NAD to 3 - NADH and 1 FAD to FADH2 (like NADH it donates its e to the electron transport chain but at a lower energy level) • One step for the production of GTP (substrate level phosphorylation; GTP can be converted to ATP) Review with Figure 5.13 5 Biol 3400 Tortora et al- Chap 5 + pyruvate + 4 NAD + FAD → 3 CO2 + 4 NADH + 1 FADH2 + 1 GTP • TCA cycle source of key biosynthetic intermediates e.g., oxaloacetate and α-ketoglutarate are precursors to a number of amino acids acetyl-CoA → starting material for fatty acid biosynthesis 3. Oxidative phosphorylation • Reducing power (NADH and FADH2) is used to generate a proton gradient (proton motive force) • NADH - FADH2 are oxidized – electron transport carrier proteins are reduced and in the process H+ are moved across the plasma membrane (prokaryotes) or inner mitochondrial membrane (eukaryotes). This results in a proton gradient or proton motive force across the membrane. The movement of H+ across the membrane is not completely understood Chemiosmosis • Proton Gradient driving ATP synthesis • Peter Mitchell (Nobel prize in Chemistry in 1978) ATP synthase (ATPase) • F0 subunit – multimeric membrane spanning proton conducting channel • F1 – multimeric headpiece → inside of the membrane • Catalyze ADP + Pi → ATP (oxidative phosphorylation) • Highly conserved throughout all domains of life • Can also drive reverse reaction ATP → ADP + Pi • explains why some obligate fermenters have ATPase - creates proton gradients that can be used to drive
Load more

Recommended publications
  • Microbial Community Composition and Function Beneath Temperate Trees Exposed to Elevated Atmospheric Carbon Dioxide and Ozone
    Oecologia (2002) 131:236–244 DOI 10.1007/s00442-002-0868-x ECOSYSTEMS ECOLOGY Rebecca L. Phillips · Donald R. Zak William E. Holmes · David C. White Microbial community composition and function beneath temperate trees exposed to elevated atmospheric carbon dioxide and ozone Received: 1 August 2001 / Accepted: 13 December 2001 / Published online: 14 February 2002 © Springer-Verlag 2002 Abstract We hypothesized that changes in plant growth activity and microbial metabolism of cellobiose, and that resulting from atmospheric CO2 and O3 enrichment microbial processes under early-successional aspen and would alter the flow of C through soil food webs and birch species were more strongly affected by CO2 and O3 that this effect would vary with tree species. To test this enrichment than those under late-successional maple. idea, we traced the course of C through the soil microbial community using soils from the free-air CO2 and O3 Keywords Soil microorganisms · enrichment site in Rhinelander, Wisconsin. We added Carbon-13-phospholipid fatty acid analysis · either 13C-labeled cellobiose or 13C-labeled N-acetylglu- Elevated carbon dioxide · Elevated ozone · cosamine to soils collected beneath ecologically distinct Soil carbon cycling temperate trees exposed for 3 years to factorial CO2 –1 (ambient and 200 µl l above ambient) and O3 (ambient and 20 µl l–1 above ambient) treatments. For both labeled Introduction substrates, recovery of 13C in microbial respiration increased beneath plants grown under elevated CO2 by Human activity has increased the concentration of CO2 29% compared to ambient; elevated O3 eliminated this and O3 in the earth’s troposphere (Barnola et al.
    [Show full text]
  • The Electron Transport Chain in Anaerobically Functioning Eukaryotes
    rl BIOCHIMICA ET BIOPHYSICA ACTA II BBt ELSEVIER Biochimica et Biophysica Acta, 1365 (1998) 71-78 The electron transport chain in anaerobically functioning eukaryotes Aloysius G.M. Tielens*, Jaap J. Van Hellemond Laboratory of Veterinary Biochemistry and Institute for Biomembranes, Utrecht University, P.O. Box 80176, 3508 TD Utrecht, The Netherlands Received 27 January 1998; received in revised form 26 February 1998; accepted 2 March 1998 Abstract Many lower eukaryotes can survive anaerobic conditions via a fermentation pathway that involves the use of the reduction of endogenously produced fumarate as electron sink. This fumarate reduction is linked to electron transport in an especially adapted, anaerobically functioning electron-transport chain. An aerobic energy metabolism with Krebs cycle activity is accompanied by electron transfer from succinate to ubiquinone via complex II of the respiratory chain. On the other hand, in an anaerobic metabolism, where fumarate functions as terminal electron acceptor, electrons are transferred from rhodoquinone to fumarate, which is the reversed direction. Ubiquinone cannot replace rhodoquinone in the process of fumarate reduction in vivo, as ubiquinone can only accept electrons from complex II and cannot donate them to fumarate. Rhodoquinone, with its lower redox potential than ubiquinone, is capable of donating electrons to fumarate. Eukaryotic fumarate reductases were shown to interact with rhodoquinone (a benzoquinone), whereas most prokaryotic fumarate reductases interact with the naphtoquinones mena- quinone and demethylmenaquinone. Fumarate reductase, the enzyme essential for the anaerobic functioning of many eukaryotes, is structurally very similar to succinate dehydrogenase, the Krebs cycle enzyme catalysing the reverse reaction. In prokaryotes these enzymes are differentially expressed depending on the external conditions.
    [Show full text]
  • Biol 1020: Photosynthesis
    Chapter 10: Photosynthesis Energy and Carbon Sources Electromagnetic Spectrum and Light Chloroplasts Photosynthesis Overview Light Reactions C3 Cycle Photorespiration Supplemental Carbon Fixation: C4 and CAM pathways . • List and differentiate the 4 possible groups of organisms based on how they obtain energy and useful carbon. Classification by Energy and Carbon Sources energy source chemotrophs can only get energy directly from chemical compounds phototrophs can get energy directly from light (these organisms can use chemical compounds as energy sources as well) . Classification by Energy and Carbon Sources carbon source autotrophs can fix carbon dioxide, thus they can use CO2 as a carbon source heterotrophs cannot fix CO2; they use organic molecules from other organisms as a carbon source . Classification by Energy and Carbon Sources combined, these leads to 4 possible groups: photoautotrophs – carry out photosynthesis use light energy to fix CO2 store energy in chemical bonds of organic molecules includes green plants, algae, and some bacteria photoheterotrophs – use light energy but cannot fix CO2; some nonsulfur purple bacteria chemoautotrophs – obtain energy from reduced inorganic molecules and use some of it to fix CO2; some bacteria chemoheterotrophs – use organic molecules as both carbon and energy sources dependent completely on other organisms for energy capture and carbon fixation includes all animals, all fungi, most protists, and most bacteria . • List and differentiate the 4 possible groups of
    [Show full text]
  • IB HL Biology: Ecology Review Fall 2017 Populations 1. Define the Following Terms Associated with Population Ecology; Population and Carrying Capacity
    IB HL Biology: Ecology Review Fall 2017 Populations 1. Define the following terms associated with population ecology; population and carrying capacity. 2. What processes contribute to changes in population size? 3. What are some factors which can increase the carrying capacity of a population? Decrease? 4. What is quadrat sampling? When would it be used? Communities 5. Define the following terms; community, autotroph, heterotroph, producer, primary consumer, secondary consumer, detritivore and saprotroph. 6. What is the initial energy source for all communities? 7. Be able to read food webs and determine the trophic level of different species. 8. Choose 2 regions below and determine the Simpson’s Diversity Index value for these regions. Which region is more diverse? A. An area of the Black Forest in Germany contains 134 pitch pines, 24 douglas firs, and 53 red pines. B. A meadow contains 1532 chestnut oaks, 342 black cherry trees, 12 white ash trees, and 1022 yellow birches. C. You school science classroom contains 12 beetles, 34 termites, 84 ants, 93 fleas, and 1 butterfly. D. An African park contains 15 lions, 94 giraffes, 1000 wildebeests, 50 elephants, and 5 hyenas. Choose more areas if you need more practice. 9. What is a keystone species? 10. Distinguish between primary and secondary succession. Ecosystems 11. What is an ecosystem? 12. Explain the 10% rule of energy transfer. How is the energy lost between trophic levels? 13. Review the Carbon Cycle. What are the main sources of carbon dioxide on earth? 14. Review the Nitrogen Cycle. 15. Distinguish between Gross Primary Productivity and Net Primary Productivity.
    [Show full text]
  • Chapter 11 – PROKARYOTES: Survey of the Bacteria & Archaea
    Chapter 11 – PROKARYOTES: Survey of the Bacteria & Archaea 1. The Bacteria 2. The Archaea Important Metabolic Terms Oxygen tolerance/usage: aerobic – requires or can use oxygen (O2) anaerobic – does not require or cannot tolerate O2 Energy usage: autotroph – uses CO2 as a carbon source • photoautotroph – uses light as an energy source • chemoautotroph – gets energy from inorganic mol. heterotroph – requires an organic carbon source • chemoheterotroph – gets energy & carbon from organic molecules …more Important Terms Facultative vs Obligate: facultative – “able to, but not requiring” e.g. • facultative anaerobes – can survive w/ or w/o O2 obligate – “absolutely requires” e.g. • obligate anaerobes – cannot tolerate O2 • obligate intracellular parasite – can only survive within a host cell The 2 Prokaryotic Domains Overview of the Bacterial Domain We will look at examples from several bacterial phyla grouped largely based on rRNA (ribotyping): Gram+ bacteria • Firmicutes (low G+C), Actinobacteria (high G+C) Proteobacteria (Gram- heterotrophs mainly) Gram- nonproteobacteria (photoautotrophs) Chlamydiae (no peptidoglycan in cell walls) Spirochaetes (coiled due to axial filaments) Bacteroides (mostly anaerobic) 1. The Gram+ Bacteria Gram+ Bacteria The Gram+ bacteria are found in 2 different phyla: Firmicutes • low G+C content (usually less than 50%) • many common pathogens Actinobacteria • high G+C content (greater than 50%) • characterized by branching filaments Firmicutes Characteristics associated with this phylum: • low G+C Gram+ bacteria
    [Show full text]
  • Sulphate-Reducing Bacteria's Response to Extreme Ph Environments and the Effect of Their Activities on Microbial Corrosion
    applied sciences Review Sulphate-Reducing Bacteria’s Response to Extreme pH Environments and the Effect of Their Activities on Microbial Corrosion Thi Thuy Tien Tran 1 , Krishnan Kannoorpatti 1,* , Anna Padovan 2 and Suresh Thennadil 1 1 Energy and Resources Institute, College of Engineering, Information Technology and Environment, Charles Darwin University, Darwin, NT 0909, Australia; [email protected] (T.T.T.T.); [email protected] (S.T.) 2 Research Institute for the Environment and Livelihoods, College of Engineering, Information Technology and Environment, Charles Darwin University, Darwin, NT 0909, Australia; [email protected] * Correspondence: [email protected] Abstract: Sulphate-reducing bacteria (SRB) are dominant species causing corrosion of various types of materials. However, they also play a beneficial role in bioremediation due to their tolerance of extreme pH conditions. The application of sulphate-reducing bacteria (SRB) in bioremediation and control methods for microbiologically influenced corrosion (MIC) in extreme pH environments requires an understanding of the microbial activities in these conditions. Recent studies have found that in order to survive and grow in high alkaline/acidic condition, SRB have developed several strategies to combat the environmental challenges. The strategies mainly include maintaining pH homeostasis in the cytoplasm and adjusting metabolic activities leading to changes in environmental pH. The change in pH of the environment and microbial activities in such conditions can have a Citation: Tran, T.T.T.; Kannoorpatti, significant impact on the microbial corrosion of materials. These bacteria strategies to combat extreme K.; Padovan, A.; Thennadil, S. pH environments and their effect on microbial corrosion are presented and discussed.
    [Show full text]
  • The Reaction Center of Green Sulfur Bacteria1
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Biochimica et Biophysica Acta 1507 (2001) 260^277 www.bba-direct.com Review The reaction center of green sulfur bacteria1 G. Hauska a;*, T. Schoedl a, Herve¨ Remigy b, G. Tsiotis c a Lehrstuhl fu«r Zellbiologie und P£anzenphysiologie, Fakulta«tfu«r Biologie und Vorklinische Medizin, Universita«t Regensburg, 93040 Regenburg, Germany b Biozentrum, M.E. Mu«ller Institute of Microscopic Structural Biology, University of Basel, CH-4056 Basel, Switzerland c Division of Biochemistry, Department of Chemistry, University of Crete, 71409 Heraklion, Greece Received 9 April 2001; received in revised form 13 June 2001; accepted 5 July 2001 Abstract The composition of the P840-reaction center complex (RC), energy and electron transfer within the RC, as well as its topographical organization and interaction with other components in the membrane of green sulfur bacteria are presented, and compared to the FeS-type reaction centers of Photosystem I and of Heliobacteria. The core of the RC is homodimeric, since pscA is the only gene found in the genome of Chlorobium tepidum which resembles the genes psaA and -B for the heterodimeric core of Photosystem I. Functionally intact RC can be isolated from several species of green sulfur bacteria. It is generally composed of five subunits, PscA^D plus the BChl a-protein FMO. Functional cores, with PscA and PscB only, can be isolated from Prostecochloris aestuarii. The PscA-dimer binds P840, a special pair of BChl a-molecules, the primary electron acceptor A0, which is a Chl a-derivative and FeS-center FX.
    [Show full text]
  • Assessing the Chemistry and Bioavailability of Dissolved Organic Matter from Glaciers and Rock Glaciers
    RESEARCH ARTICLE Assessing the Chemistry and Bioavailability of Dissolved 10.1029/2018JG004874 Organic Matter From Glaciers and Rock Glaciers Special Section: Timothy Fegel1,2 , Claudia M. Boot1,3 , Corey D. Broeckling4, Jill S. Baron1,5 , Biogeochemistry of Natural 1,6 Organic Matter and Ed K. Hall 1Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO, USA, 2Rocky Mountain Research 3 Key Points: Station, U.S. Forest Service, Fort Collins, CO, USA, Department of Chemistry, Colorado State University, Fort Collins, • Both glaciers and rock glaciers CO, USA, 4Proteomics and Metabolomics Facility, Colorado State University, Fort Collins, CO, USA, 5U.S. Geological supply highly bioavailable sources of Survey, Reston, VA, USA, 6Department of Ecosystem Science and Sustainability, Colorado State University, Fort Collins, organic matter to alpine headwaters CO, USA in Colorado • Bioavailability of organic matter released from glaciers is greater than that of rock glaciers in the Rocky Abstract As glaciers thaw in response to warming, they release dissolved organic matter (DOM) to Mountains alpine lakes and streams. The United States contains an abundance of both alpine glaciers and rock • ‐ The use of GC MS for ecosystem glaciers. Differences in DOM composition and bioavailability between glacier types, like rock and ice metabolomics represents a novel approach for examining complex glaciers, remain undefined. To assess differences in glacier and rock glacier DOM we evaluated organic matter pools bioavailability and molecular composition of DOM from four alpine catchments each with a glacier and a rock glacier at their headwaters. We assessed bioavailability of DOM by incubating each DOM source Supporting Information: with a common microbial community and evaluated chemical characteristics of DOM before and after • Supporting Information S1 • Data Set S1 incubation using untargeted gas chromatography–mass spectrometry‐based metabolomics.
    [Show full text]
  • Fermentation and Anaerobic Decomposition in a Hot Spring
    Fermentation and anaerobic decomposition in a hot spring microbial mat by Karen Leigh Anderson A thesis submitted in partial fulfillment of requirements for the degree of Master of Science in Microbiology Montana State University © Copyright by Karen Leigh Anderson (1984) Abstract: Fermentation was investigated in a low sulfate hot spring microbial mat (Octopus Spring) according to current models on anaerobic decomposition. The mat was studied to determine what fermentation products accumulated, where in the mat they accumulated, and what factors affected their accumulation. Mat samples were incubated under dark anaerobic conditions to measure accumulation of fermentation products. Acetate and propionate (ca. 3:1) were the major products to accumulate in a 55&deg,C mat. Other products accumulated to a much lesser extent. Incubation of mat samples of varying thickness showed that fermentation occurred in the top 4mm of the mat. This has interesting implications for fermentative organisms in the mat due to the diurnal changes in mat oxygen concentrations. Fermentation measured in mat samples collected at various temperatures (50&deg,-70°C) showed acetate and propionate to be the major accumulation products. According to the interspecies hydrogen transfer model, the hydrogen concentration in a system affects the types of fermentation products produced. At a 65° C site, with natural high hydrogen levels, and at a 55°C site, with active methanogenesis, fermentation product accumulation was compared. There was a greater ratio of reduced fermentation products to acetate, with the exception of propionate, at 65°C. Ethanol accumulated at the 65°C site, as did lactate, though to a lesser extent.
    [Show full text]
  • Redox Potential of the Terminal Quinone Electron Acceptor QB in Photosystem II Reveals the Mechanism of Electron Transfer Regulation
    Redox potential of the terminal quinone electron acceptor QB in photosystem II reveals the mechanism of electron transfer regulation Yuki Kato1, Ryo Nagao, and Takumi Noguchi1 Division of Material Science, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan Edited by Pierre A. Joliot, Institut de Biologie Physico-Chimique, Paris, France, and approved December 4, 2015 (received for review October 12, 2015) Photosystem II (PSII) extracts electrons from water at a Mn4CaO5 (Em values). Both forward and backward electron transfers are cluster using light energy and then transfers them to two plas- important; backward electron transfers control charge recombina- toquinones, the primary quinone electron acceptor QA and the tion in PSII, and this serves as photoprotection for PSII proteins secondary quinone electron acceptor QB. This forward electron (5, 14–17). PSII involves specific mechanisms to regulate for- transfer is an essential process in light energy conversion. Mean- ward and backward electron transfer reactions in response to while, backward electron transfer is also significant in photopro- environmental changes. For instance, in strong light, some spe- tection of PSII proteins. Modulation of the redox potential (Em) gap cies of cyanobacteria increase the Em of Pheo to facilitate charge of QA and QB mainly regulates the forward and backward electron recombination. Specifically, they exchange D1 subunits origi- transfers in PSII. However, the full scheme of electron transfer nating from different psbA genes to change the hydrogen bond regulation remains unresolved due to the unknown Em value of interactions of Pheo (16–20). On the other hand, it was found QB. Here, for the first time (to our knowledge), the Em value of QB that impairment of the Mn4CaO5 cluster led to a significant in- reduction was measured directly using spectroelectrochemistry in crease in the Em of QA by ∼150 mV (21–27).
    [Show full text]
  • Synthesis and Photoinduced Electron Transfer of Donor-Sensitizer-Acceptor Systems
    Synthesis and Photoinduced Electron Transfer of Donor-Sensitizer-Acceptor Systems Yunhua Xu Stockholm University 2005 1 Synthesis and Photoinduced Electron Transfer of Donor-Sensitizer-Acceptor Systems Akademisk avhandling som för avläggande av filosofie doktorsexamen vid Stockholms Universitet, tillsammans med arbetena I-VII, offentligen kommer att försvaras i Magnélisalen, Kemiska övnings-laboratoriet, Svante Arrhenius väg 16, onsdagen den 20 april 2005, klockan 10.00. Av Yunhua Xu Avhandlingen försvaras på engelska Institutionen för organisk kemi ISBN 91-7155-034-8 pp 1-53 Arrheniuslaboratoriet Stockholm 2005 Stockholms Universitet 106 91 Stockholm Abstract Artificial systems involving water oxidation and solar cells are promising ways for the conversion of solar energy into fuels and electricity. These systems usually consist of a photosensitizer, an electron donor and / or an electron acceptor. This thesis deals with the synthesis and photoinduced electron transfer of several donor-sensitizer- acceptor supramolecular systems. The first part of this thesis describes the synthesis and properties of two novel dinuclear ruthenium complexes as electron donors to mimic the donor side reaction of Photosystem II. These two Ru2 complexes were then covalently linked to ruthenium trisbipyridine and the properties of the resulting trinuclear complexes were studied by cyclic voltammetry and transient absorption spectroscopy. The second part presents the synthesis and photoinduced electron transfer of covalently linked donor-sensitizer supramolecular systems in the presence of TiO2 as electron acceptors. Electron donors are tyrosine, phenol and their derivatives, and dinuclear ruthenium complexes. Intramolecular electron transfer from the donor to the oxidized sensitizer was observed by transient absorption spectroscopy after light 2+ excitation of the Ru(bpy)3 moiety.
    [Show full text]
  • Principles of Ecology Section ●2 Flow of Energy in an Ecosystem
    chapter 2 Principles of Ecology section ●2 Flow of Energy in an Ecosystem -!). )DEA Before You Read Autotrophs capture energy, making it available for all If a pet had to survive without your care, how would its diet members of a food web. change? Write your ideas on the lines below. Read about how What You’ll Learn organisms get food and energy in their environment. ■ the fl ow of energy through an ecosystem ■ food chains, food webs, and pyramid models 3TUDY#OACH Read to Learn Make Flash Cards Make a fl ash card for each question Energy in an Ecosystem heading in this section. On the One way to study the interactions within an ecosystem is to back of the fl ash card, write the trace how energy fl ows through the system. All organisms are answer to the question. Use the classifi ed by the way they obtain energy. fl ash cards to review what you have learned. How do autotrophs obtain energy? All green plants and other organisms that produce their own food are the primary producers of food in an ecosystem. They are called autotrophs. An autotroph (AW tuh trohf) is an organism that captures energy from sunlight or inorganic substances to produce food. Autotrophs make energy available for all other organisms in the ecosystem. How do heterotrophs differ from autotrophs? A heterotroph (HE tuh roh trohf), also called a consumer, is an organism that obtains energy by consuming other organisms. A heterotroph that consumes only plants is an herbivore (HUR buh vor). Cows, rabbits, and grasshoppers are herbivores.
    [Show full text]