DOCSLIB.ORG

Generation of an Electrochemical Proton Gradient in Streptococcus Cremoris by Lactate Efflux (Fermentation/Transport) ROEL OTTO, ANTON S

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Generation of an Electrochemical Proton Gradient in Streptococcus Cremoris by Lactate Efflux (Fermentation/Transport) ROEL OTTO, ANTON S Proc. Natl. Acad. Sci. USA Vol. 77, No. 9, pp. 5502-5506, September 1980 Microbiology Generation of an electrochemical proton gradient in Streptococcus cremoris by lactate efflux (fermentation/transport) ROEL OTTO, ANTON S. M. SONNENBERG, HANS VELDKAMP, AND WIL N. KONINGS* Department of Microbiology, Biological Centre, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands Communicated by Peter Mitchell, June 9, 1980 ABSTRACT Recently an energy-recycling model was pro- solute will occur when [(n - 1)AT - nZApH] < -Z posed that postulates the generation of an electrochemical log(A-/A-,) and the energy of the solute gradient then will be gradient in fermentative bacteria by carrier-mediated excretion into of the of metabolic end products in symport with protons. In this paper converted energy electrochemical proton gra- experimental support for this model is given. In batch cultures dient. of Streptococcus cremoris with glucose as the sole energy source During fermentation, excretion of metabolic end products the maximal specific growth rate decreased by 30% when the via a carrier in symport with proton(s) can occur only when the external lactate concentration was decreased from 50 to 90 mM. outwardly directed driving force supplied by the chemical end In the same range of external lactate concentrations the molar product gradient exceeds the inwardly directed driving force growth yield Y for glucose as measured in energy-limited che- supplied by the electrochemical gradient. The excretion of end mostat cultures also showed a 30% drop. From ynaxtose values of S. cremoris grown in the presence and absence of added lactate products will then lead to the generation of an electrochemical it was calculated that the net energy ain from the lactate efflux gradient. Michels et al. (1) calculated the generation of the system was at least 12%. Lactate effux from de-energized cells electrochemical gradient for a model cell that excreted lactate loaded with lactate could drive the uptake of leucine. This up- in symport with a variable number (1 or 2) of protons. It was take was sensitive to carbonylcyanide p-trifluoromethoxy- concluded that in these cells lactate efflux could account for an phenylhydrazone and was only partly inhibited by dicyclo- additional 30% of metabolic energy. hexylcarbodiimide (DCCD). The limited inhibition by DCCD of lactate-induced leucine uptake indicates that ATP hydrolysis In this paper experimental support is given for this energy- was not the driving force for transport of leucine. recycling model. The effects of external lactate on maximum Uptake studies with the lipophilic cation tetraphenylphos- specific growth rate, cell yield, and maintenance requirements phonium demonstrated that lactate efflux increased the elec- of Streptococcus cremoris were studied. The chemostat culture trical potential across the membrane by 51 mV. The generation technique was used in this study because it allowed a quanti- of an electrical potential by lactate efflux and the demonstration tation of the effects of lactate on energy metabolism under of a potassium efflux-induced uptake of lactate indicates that energy-limited conditions. In addition, we investigated whether lactate is translocated across the membrane by a symport system lactate efflux could generate an electrochemical gradient in with more than one proton. energy-depleted cells. The energy-recycling model recently proposed by Michels et al. (1) is an extension of the chemosmotic model given by MATERIALS AND METHODS Mitchell (2-4). The energy-recycling model postulates that Culture Conditions. S. cremoris Wg2 was obtained from the carrier-mediated excretion of metabolic end products can lead Dutch Institute of Dairy Research (Nederlands Instituut voor to the generation of an electrochemical gradient across the Zuivelouderzoek, Ecle, The Netherlands). The organism was cytoplasmic membrane, thus providing metabolic energy to routinely maintained in 10% (wt/vol) skimmed milk and stored the cell. The proposed model is based on the following consid- at -20'C. From the milk cultures S. cremoris was transferred erations. to a complex MRS medium (6) and subsequently to a chemically The driving force for translocation of solute A across the defined medium (7). Batch cultures were grown anaerobically cytoplasmic membrane by a solute-proton symport system (2) at 30'C in screw-capped tubes (diameter 10 mm, length 10 cm) is the sum of the electrochemical gradient and the solute gra- or in pH-controlled 3-liter erlenmeyer flasks. Chemostat cul- dient (5): tures were grown anaerobically under N2 atmosphere in glass chemostats with a working volume of 200 ml at 30'C and Z log(A-/A- t) + (n - 1)A' - nZApH, controlled pH of 6.3 as described by Laanbroek et al. (8). in which AiT is the electrical potential and ApH is the pH Maximal Specific Growth Rate in Batch Cultures. Growth gradient across the cytoplasmic membrane, n is the number of rate was determined from the increase of OD660 during expo- protons transported in symport with A-; Z is 2.3RT/F (R, gas nential growth. OD6co was followed by placing the screw- constant; T, absolute temperature; F, Faraday constant); and capped tubes in special adaptors in a Vitatron UC 200 spec- A- and A- t are the concentrations of A- in the cell and the trophotometer (Vitatron Scientific Instruments, Dieren, The external medium, respectively. A steady-state level of accu- Netherlands). mulation is reached when this driving force is zero, thus when Cell Suspensions for Transport Studies. Suspensions were (n - 1)AT - nZApH =-Z log(Aj-/A- t). According to this obtained from 3-liter batch cultures (OD6W1 = 0.8). The cells equation accumulation of solute A- will occur when [(n - were washed twice with 2 liters of 40mM potassium phosphate, 1)AT - nZApH] > -Z log(Aj-/A- t). However, excretion of pH 7.0, at room temperature, resuspended in this buffer to a The publication costs of this article were defrayed inpart by page Abbreviations: MeSGal, methyl 1-thio-3-D-galactopyranoside; FCCP, charge payment. This article must therefore be hereby marked "ad- carbonylcyanide p-trifluoromethoxyphenylhydrazone; DCCD, di- vertisement" in accordance with 18 U. S. C. §1734 solely to indicate cyclohexylcarbodiimide; Ph4P+, tetraphenylphosphonium. this fact. * To whom reprint requests should be addressed. 5502 Downloaded by guest on October 2, 2021 Microbiology: Otto et al. Proc. Natl. Acad. Sci. USA 77 (1980) 5503 density of 100 mg/ml (dry wt) and stored as 0.25-ml samples described by Bakker et al. (17). For batch-grown cells the in- in liquid nitrogen. tracellular volume was 3.79 ,l/mg of cell protein. De-energization of S. cremoris. A 0.25-ml cell suspension Materials. Radioactive labeled leucine and L-lactate were was thawed quickly and washed twice at room temperature obtained from the Radiochemical Centre (Amersham). [3H]- with 10 ml of choline/Hepes/KCI buffer (10 mM choline/ Ph4P+ was generously supplied by H. R. Kaback (Roche Insti- Hepes, pH 7.0, and 2 mM KCI). Methyl I-thio-f3-D-galacto- tute of Molecular Biology, Nutley, NJ). Carbonylcyanide p- pyranoside (MeSGal) was added to the washed cell suspension trifluoromethoxyphenylhydrazone (FCCP) and dicyclohex- [2.5 mg/ml (dry wt)] to a final concentration of 1 mM (9). The ylcarbodiimide (DCCD) were dissolved in absolute ethanol. cell suspension was incubated for 1 hr at room temperature. The Additions to incubation mixtures were made to maximal eth- cells were washed twice with 10 ml of choline/Hepes/KCI anol concentrations of 1% (vol/vol). buffer and finally resuspended in this buffer to a density of 100 mg/ml (dry wt). RESULTS Loading of De-energized Cells with Lactate or Chloride. Effects of External L-Lactate on Growing Cells of S. cre- De-energized cells (0.25 ml) [100 mg/ml (dry wt)] were washed moris. According to the energy-recycling model, efflux of twice with 10 ml of choline/Hepes/KCI buffer supplemented lactate from S. cremoris, growing anaerobically on glucose, with 50 mM choline L-lactate. The suspension was acidified to should result in the generation of an electrochemical proton pH 4.3 with 0.2 M L-lactic acid and incubated at room tem- gradient that contributes to the energy metabolism of the cell. perature-for 10 min. Subsequently the suspension was neu- A decrease of the lactate gradient across the cytoplasmic tralized with 0.2 M choline hydroxide and incubated for an membrane will reduce the energy yield and consequently will additional 30 min at room temperature. Finally the cells were lower the molar growth yield as well as the maximal specific concentrated to a cell density of 100 mg/ml (dry wt). Loading growth rate, if it is assumed that this is determined by the rate of de-energized cells with choline chloride was performed in of ATP supply. the same way except that choline lactate and L-lactic acid were The effect of increasing extracellular L-lactate concentrations replaced by choline chloride and HCI, respectively. on the maximal specific growth rate of S. cremoris, grown Uptake of L-Leucine and Ph4P+. A sample (1 Ml) of un- anaerobically in a synthetic medium in batch culture, is shown loaded or loaded cells [100 mg/ml (dry wt)] was diluted into in Fig. 1. This effect is clearly different from that of other 100 Ml of 10 mM choline/Hepes/KCI buffer containing 2.85 compounds, such as sodium propionate and NaCI (Fig. 1). The AM ['4C]leucine (351 mCi/mmol; 1 Ci = 3.7 X 1010 becquerels) latter compounds exhibited a significant inhibitory effect at or 40 MM [3H]tetraphenylphosphonium bromide (Ph4P+) (54 concentrations as low as 10 mM. Inhibition patterns with KC1, mCi/mmol) and 0-50mM choline L-lactate or 0-50mM cho- choline chloride, and potassium propionate did not differ sig- line chloride.
Load more

Recommended publications
  • Cellular Biology 1
    Cellular biology 1 INTRODUCTION • Specialized intracellular membrane-bound organelles (Fig. 1.2), such as mitochondria, Golgi apparatus, endoplasmic reticulum (ER). This chapter is an overview of eukaryotic cells, addressing • Large size (relative to prokaryotic cells). their intracellular organelles and structural components. A basic appreciation of cellular structure and function is important for an understanding of the following chapters’ information concerning metabolism and nutrition. For fur- ther detailed information in this subject area, please refer to EUKARYOTIC ORGANELLES a reference textbook. Nucleus The eukaryotic cell The nucleus is surrounded by a double membrane (nuclear Humans are multicellular eukaryotic organisms. All eukary- envelope). The envelope has multiple pores to allow tran- otic organisms are composed of eukaryotic cells. Eukaryotic sit of material between the nucleus and the cytoplasm. The cells (Fig. 1.1) are defined by the following features: nucleus contains the cell’s genetic material, DNA, organized • A membrane-limited nucleus (the key feature into linear structures known as chromosomes. As well as differentiating eukaryotic cells from prokaryotic cells) chromosomes, irregular zones of densely staining material that contains the cell’s genetic material. are also present. These are the nucleoli, which are responsible Inner nuclear Nucleus membrane Nucleolus Inner Outer Outer mitochondrial nuclear mitochondrial membrane membrane membrane Ribosome Intermembrane space Chromatin Mitochondrial Rough matrix Mitochondrial Nuclear endoplasmic ribosome pore reticulum Crista Mitochondrial mRNA Smooth Vesicle endoplasmic Mitochondrion Circular reticulum mitochondrial Proteins of the DNA Vesicle budding electron transport off rough ER Vesicles fusing system with trans face of Cytoplasm Golgi apparatus ‘Cis’ face + discharging protein/lipid Golgi apparatus ‘Trans’ face Lysosome Vesicles leaving Golgi with modified protein/lipid cargo Cell membrane Fig.
    [Show full text]
  • Passive and Active Transport
    Passive and Active Transport 1. Thermodynamics of transport 2. Passive-mediated transport 3. Active transport neuron, membrane potential, ion transport Membranes • Provide barrier function – Extracellular – Organelles • Barrier can be overcome by „transport proteins“ – To mediate transmembrane movements of ions, Na+, K+ – Nutrients, glucose, amino acids etc. – Water (aquaporins) 1) Thermodynamics of Transport • Aout <-> Ain (ressembles a chemical equilibration) o‘ • GA - G A = RT ln [A] • ∆GA = GA(in) - GA(out) = RT ln ([A]in/[A]out) • GA: chemical potential of A o‘ • G A: chemical potential of standard state of A • If membrane has a potential, i.e., plasma membrane: -100mV (inside negative) then GA is termed the electrochemical potential of A Two types of transport across a membrane: o Nonmediated transport occurs by passive diffusion, i.e., O2, CO2 driven by chemical potential gradient, i.e. cannot occur against a concentration gradient o Mediated transport occurs by dedicated transport proteins 1. Passive-mediated transport/facilitated diffusion: [high] -> [low] 2. Active transport: [low] -> [high] May require energy in form of ATP or in form of a membrane potential 2) Passive-mediated transport Substances that are too large or too polar to diffuse across the bilayer must be transported by proteins: carriers, permeases, channels and transporters A) Ionophores B) Porins C) Ion Channels D) Aquaporins E) Transport Proteins A) Ionophores Organic molecules of divers types, often of bacterial origin => Increase the permeability of a target membrane for ions, frequently antibiotic, result in collapse of target membrane potential by ion equilibration 1. Carrier Ionophore, make ion soluble in membrane, i.e. valinomycin, 104 K+/sec 2.
    [Show full text]
  • Evidence for a Respiratory Chain in the Chloroplast
    Proc. NatL Acad. Sci. USA Vol. 79, pp. 4352-4356, July 1982 Cell Biology Evidence for a respiratory chain in the chloroplast (photosynthesis/respiration/starch degradation/evolution) PIERRE BENNOUN Institut de Biologie Physico-Chimique, 13, rue Pierre et Marie Curie, 75005, Paris, France Communicated by Pierre Joliot, April 12, 1982 ABSTRACT Evidence is given for the existence ofan electron in 20 ml of 20 mM N-tris(hydroxymethyl)methylglycine(Tri- transport pathway to oxygen in the thylakoid membranes ofchlo- cine)/KOH, pH 7.8/10 mM NaCl/10 mM MgCl2/1 mM K2- roplasts (chlororespiration). Plastoquinone is shown to be a redox HPO4/0.1 M sucrose/5% Ficoll. The cell suspension was carrier common to both photosynthetic and chlororespiratory passed through a Yeda press operated at 90 kg/cm2, diluted pathways. It is shown that, in dark-adapted chloroplasts, an elec- with 200 ml of Ficoll-lacking buffer, and centrifuged, and the trochemical gradient is built up across the thylakoid membrane pellet was suspended in the same buffer. by transfer of electrons through the chlororespiratory chain as Chlorophyll fluorescence kinetics and luminescence mea- well as by reverse functioning of the chloroplast ATPases. It is surements were performed as described (9). proposed that these mechanisms ensure recycling ofthe ATP and NAD(P)H generated by the glycolytic pathway converting starch into triose phosphates. Chlororespiration is thus an 02-uptake RESULTS process distinct from photorespiration and the Mehler reaction. The plastoquinone (PQ) pool ofchloroplast is a redox carrier of The evolutionary significance of chlororespiration is discussed. the photosynthetic electron transport chain.
    [Show full text]
  • The Electrochemical Gradient of Protons and Its Relationship to Active Transport in Escherichia Coli Membrane Vesicles
    Proc. Natl. Acad. Sci. USA Vol. 73, No. 6, pp. 1892-1896, June 1976 Biochemistry The electrochemical gradient of protons and its relationship to active transport in Escherichia coli membrane vesicles (flow dialysis/membrane potential/energy transduction/lipophilic cations/weak acids) SOFIA RAMOS, SHIMON SCHULDINER*, AND H. RONALD KABACK The Roche Institute of Molecular Biology, Nutley, New Jersey 07110 Communicated by B. L. Horecker, March 17, 1976 ABSTRACT Membrane vesicles isolated from E. coli gen- presence of valinomycin), a respiration-dependent membrane erate a trans-membrane proton gradient of 2 pH units under potential (AI, interior negative) of approximately -75 mV in appropriate conditions when assayed by flow dialysis. Using E. coli membrane vesicles has been documented (6, 13, 14). the distribution of weak acids to measure the proton gradient (ApH) and the distribution of the lipophilic cation triphenyl- Moreover it has been shown that the potential causes the ap- methylphosphonium to measure the electrical potential across pearance of high affinity binding sites for dansyl- and azido- the membrane (AI), the vesicles are shown to generate an phenylgalactosides on the outer surface of the membrane (4, electrochemical proton gradient (AiH+) of approximately -180 15) and that the potential is partially dissipated as a result of mV at pH 5.5 in the presence of ascorbate and phenazine lactose accumulation (6). Although these findings provide ev- methosulfate, the major component of which is a ApH of about idence for the chemiosmotic hypothesis, it has also been dem- -110 mV. As external pH is increased, ApH decreases, reaching o at pH 7.5 and above, while AI remains at about -75 mV and onstrated (6, 16) that vesicles are able to accumulate lactose and internal pH remains at pH 7.5.
    [Show full text]
  • Photosynthesis and Respiration
    18 Photosynthesis and Respiration ATP is the energy currency of the cell Goal To understand how energy from sunlight is harnessed to Cells need to carry out many reactions that are energetically unfavorable. generate chemical energy by photosynthesis and You have seen some examples of these non-spontaneous reactions in respiration. earlier chapters: the synthesis of nucleic acids and proteins from their corresponding nucleotide and amino acid building blocks and the transport Objectives of certain ions against concentration gradients across a membrane. In many cases, unfavorable reactions like these are coupled to the hydrolysis of ATP After this chapter, you should be able to: in order to make them energetically favorable under cellular conditions; we • Explain the concepts of oxidation and have learned that for these reactions the free energy released in breaking reduction. the phosphodiester bonds in ATP exceeds the energy consumed by the • Explain how light energy generates an uphill reaction such that the sum of the free energy of the two reactions is electrochemical gradient. negative (ΔG < 0). To perform these reactions, cells must then have a way • Explain how an electrochemical of generating ATP efficiently so that a sufficient supply is always available. gradient generates chemical energy. The amount of ATP used by a mammalian cell has been estimated to be on the order of 109 molecules per second. In other words, ATP is the principal • Explain how chemical energy is harnessed to fix carbon dioxide. energy currency of the cell. • Explain how glucose is used to generate How does the cell produce enough ATP to sustain life and what is the source ATP anaerobically.
    [Show full text]
  • 3. Transport Can Be Active Or Passive. •Passive Transport Is Movement
    3. Transport can be active or passive. F 6-3 Taiz. Microelectrodes are used to measure membrane •Passive transport is movement down an electrochemical potentials across cell membrane gradient. •Active transport is movement against an electrochemical gradient. What is an electrochemical gradient? How is it formed? Passive and active transport of ions result in electric potential difference across membranes. •Movement of an uncharged mol Is dependent on conc. gradient alone. •Movement of an ion depends on the electric gradient and the conc. gradient. •Diffusion potential- Pump potential- How do you know if an ion is moving uphill or downhill? Nernst Eq What is the driving force for uphill movement? A) ATP ; b) H+ gradient 6-5. Pump potential and diffusion potential. How can we determine whether an ion moves in or out by active or passive transport? Nernst equation states that at equilibrium the difference in concentration of an ion between two compartments is balanced by the voltage difference. Thus it can predict the ion conc at equilibrium at a certain ΔE. Very useful to predict active or passive transport of an ion. Fig. 6-4, Taiz. Passive and active transporters. Tab 6-1, Taiz . Using the Nernst equation to predict ion conc. at equilibrium when the Cell electrical potential, Δψ = -110 mV ---------------------------------------------------------------------------------------- Ext Conc. Ion Internal concentration (mM) Summary: In general observed Nernst (Predicted) ---------------------------------------------------------------------------------------- Cation uptake: passive 1 mM K+ 75 mM 74 Cation efflux: active 1 mM Na+ 8 mM 74 1 mM Ca2+ 2 mM 5,000 Anion uptake: active 0.2 mM Mg2+ 3 1,340 Anion release: passive - 2 mM NO3 5 mM 0.02 1 Cl- 10 mM 0.01 - 1H2PO4 21 0.01 ---------------------------------------------------------------------------------------- 1 6-10.
    [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]
  • Electron Transport Generates a Proton Gradient Across the Membrane
    Electron Transport Generates a Proton Gradient Across the Membrane Each of respiratory enzyme complexes couples the energy released by electron transfer across it to an uptake of protons from water in the mitochondrial matrix, accompanied by the release of protons on the other side of the membrane into the intramembrane space. As result, the energetically favorable flow of electrons along the electron- transport chain pumps protons across the membrane out of the matrix. This event creates electrochemical protons across the inner membrane. The Proton Gradient Drives ATP Synthesis The electrochemical proton gradient across the inner mitochondrial membrane is used to drive ATP synthesis in the process of oxidative Phosphorylation. The device that makes this possible is a large membrane-bound enzyme called ATP synthase. This enzymes creates a hydrophilic pathway across the inner mitochondrial membrane that allows protons to follow down their electrochemical gradient. As these ions thread their way through the ATP synthase, they are used to drive the energetically unfavorable reaction between ADP and Pi. 1 Proton Gradients Produce Most of the Cell’s ATP Glycolysis alone produces a net yield of two molecules of ATP for every molecule of glucose, which is the total energy yield for the fermentation process that occur in the absence of oxygen. In contrast, during the oxidative Phosphorylation each pair of electrons donated by NADH produced mitochondria is thought to provide energy for the formation of the about 2.5 molecules of ATP, once one includes the energy needed for transporting this ATP to cytosol. Oxidative Phosphorylation also produces 1.5 ATP molecules per electron pair of FADH2, or from the NADH molecules produced by glycolysis in the cytosol.
    [Show full text]
  • A) Thylakoid Membrane
    1)Which incorrectly matches process and location? a) Oxygen gas is produced—the thylakoid space b) Activated chlorophyll donates an electron—the thylakoid membranes c) NADPH is oxidized to NADP+—the stroma d) ATP is produced—the intermembrane space e) Rubisco catalyzes carbon fixation—the stroma 1)Which incorrectly matches process and location? a) Oxygen gas is produced—the thylakoid space b) Activated chlorophyll donates an electron—the thylakoid membranes c) NADPH is oxidized to NADP+—the stroma d) ATP is produced—the intermembrane space e) Rubisco catalyzes carbon fixation—the stroma 2)Of these events from the light reactions, which occurs first? a) Light-induced reduction of the primary electron acceptor in the reaction center of PS II. b) While being split, electrons are taken out of water. c) Donation of electrons from reduced Pq to the cytochrome complex. d) Acceptance of electrons by Pc from the cytochrome complex. e) Pq gets electrons from the reduced primary electron acceptor of PS II. 2)Of these events from the light reactions, which occurs first? a) Light-induced reduction of the primary electron acceptor in the reaction center of PS II. b) While being split, electrons are taken out of water. c) Donation of electrons from reduced Pq to the cytochrome complex. d) Acceptance of electrons by Pc from the cytochrome complex. e) Pq gets electrons from the reduced primary electron acceptor of PS II. 3)When donating its activated electron, the chlorophyll in photosystem II is a very powerful oxidizing agent. This is best shown by its ability to a) make use of a proton electrochemical gradient to drive the formation of ATP.
    [Show full text]
  • Passive Transport Requires Atp
    Passive Transport Requires Atp Liege Baron never analogize so glowingly or jabbed any auklet remonstratingly. Is Van long-term or garnisheedlitigious after some vicinal osteoplasties Salvador purloin hurtlessly so edgeways? or tittupped Photosensitive facultatively. and incorrect Filbert often ATP pumps to synthesize ATP. Liquid Phase Separation in Biology. In this animated object, cannot easily diffuse through. This, you can ask the network administrator to run a scan across the network looking for misconfigured or infected devices. Before moving on, which is a sac surrounded by a membrane, so sodium tends to enter the cell while potassium leaves. They essentially swallow the dust to keep your lungs healthy. Contrast Prokaryotic cells vs. While secondary active transport consumes ATP to generate the gradient down which a molecule is moved, white blood cells, the macrophages can attack the dust and surround it. Because of the pump, and graduate levels. Both primary and secondary bile acids are absorbed into the portal blood at the terminal ileum. The protein is then dephosphorylated and undergoes an additional conformational change, and this is the exact opposite of what we see compared to sodium. There are several different types of this easy movement of molecules. The arrows in fig. What is the Endomembrane system within Eurkaryotic cells? Membrane Transport and Metabolism. When the phosphate separates from the proteins, and in a few neurons it is two sodium ions for one potassium ion. Images are used with permission as required. Protein channel proteins, change conformation and release glucose on the other side of the membrane. Here, secretory vesicles migrate to the cell membrane where the vesicular membrane fuses with the plasma membrane, the intracellular sodium will be higher.
    [Show full text]
  • Principle of Chemiosmotic Mechanism Tianyi Shi 2019-10-15
    Principle of chemiosmotic mechanism Tianyi Shi 2019-10-15 1 SAQ Explain the difference between electrochemical gradient, pH gradient and membrane poten- tials. How can they be measured and how are these related to chemiosmotic mechanism. The electrochemical gradient describes the difference in chemical stability of ions (typically protons), between two aqueous compartments separated by a non-conducting and non-permeable membrane (typically a energy- transducing membrane such as mitochondrial inner membrane). It is quantified by the difference in Gibbs’ free energy, ∆G, or its molar equivalent, chemical potential, ∆µ, of the ion species (proton) between the two compartments. Usually, electrochemical gradient is used in studying processes coupled with H+ movement across a membrane, where one side is positively charged and has a high H+ and the other side with -ve charge and low H+. These are denoted by P and N sides, respectively, and the ‘gradients’ are often defined as the value of the corresponding parameter on the N side minus its value on the P side. The electrochemical gradient is the sum of pH gradient (concentration gradient) and membrane potential (electrical gradient). pH gradient is the (log-transformed) difference in the concentration of protons, H+, across the membrane. Protons tend to move down its concentration gradient to maximise the entropy of the whole system, and this tendency, i.e. potetial energy is the “chemical” part of the electrochemical potential. Intracellular/intra- orgenellar pH can be measured with pH-sensitive microelectrodes, nuclear magnetic resonance, or pH-sensitive fluorescent proteins (Loiselle and Casey 2010). Low-RMM weak acids and bases can equilibrate across the membrane independent of the membrane potential.
    [Show full text]
  • Lecture 37 & 38: Electron Transport Chain and Oxidative Phosphorylation
    CHM333 LECTURES 37 & 38: 4/27 – 29/13 SPRING 2013 Professor Christine Hrycyna Electron Transport and Oxidative Phosphorylation • Final stages of aerobic Mitochondrial Electron Transport oxidation of biomolecules in • How did we get here? eukaryotes occur in the mitochondrion • Summary of glycolysis glucose + 2 NAD+ + 2P + 2ADP 2 pyruvate + 2ATP + 2NADH + 2H+ • Reduced coenzymes NADH i → and FADH2 from: • Summary of the citric acid cycle (including pyruvate dehydrogenase) pyruvate + 4 NAD+ + FAD + GDP + 2 H 0 3 CO + 4NADH + 4H+ + P + GTP + FADH (1) Aerobic oxidation of 2 → 2 i 2 pyruvate by the citric acid cycle (2) Oxidation of fatty acids and amino acids Electron Transport Chain is the process by which NADH and FADH2 are oxidized and a proton gradient is formed. Electron Transport and Oxidative Phosphorylation Oxidative phosphorylation is the process of making ATP by using the proton gradient generated by the ETC. Respiration by mitochondria • Oxidation of substrates is coupled to the phosphorylation of ADP • Respiration (consumption of oxygen) proceeds only when ADP is present • The amount of O2 consumed depends upon the amount of ADP added Location of mitochondrial complexes • Inner mitochondrial membrane: a. Electron transport chain: oxidizes reduced coenzymes b. ATP synthase: machinery to synthesize ATP 280 CHM333 LECTURES 37 & 38: 4/27 – 29/13 SPRING 2013 Professor Christine Hrycyna Electron transport and oxidative phosphorylation capture the energy in the redox potential of NADH and FADH2 – 2 separate processes that are COUPLED to result in ATP production Extensive folding of IMM provides a large surface area on the matrix side to form lots of assemblies of proteins to maximize ATP production (1) Respiratory electron-transport chain (ETC) Series of enzyme complexes embedded in the inner mitochondrial membrane, which oxidize NADH and FADH2.
    [Show full text]