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4.10: Chemiosmosis - Biology

4.10: Chemiosmosis - Biology


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Several kinds of evidence support the chemiosmotic theory of ATP synthesis in chloroplasts. When isolated chloroplasts are illuminated, the medium in which they are suspended becomes alkaline — as we would predict if protons were being removed from the medium and pumped into the thylakoids (where they reduce the pH to about 4.0 or so). The interior of thylakoids can be deliberately made acid (low pH) by suspending isolated chloroplasts in an acid medium (pH 4.0) for a period of time. When these chloroplasts are then transferred to a slightly alkaline medium (pH 8.5), that is, one with a lower concentration of protons and given a supply of ADP and inorganic phosphate (Pi), they spontaneously synthesize ATP. No light is needed.

This is a direct evidence that a gradient of protons can be harnessed to the synthesis of ATP.


Chemiosmotic Theory

The Royal Swedish Academy of Sciences decided to award the 1978 Nobel Prize in Chemistry to
Dr Peter Mitchell, Glynn Research Laboratories, Bodmin, Cornwall, UK, for his contribution to the understanding of biological energy transfer through the formulation of the chemiosmotic theory.

Chemiosmotic Theory of Energy Transfer

Peter Mitchell was born in Mitcham, in the County of Surrey, England, on September 29, 1920. His parents, Christopher Gibbs Mitchell and Kate Beatrice Dorothy (née) Taplin, were very different from each other temperamentally. His mother was a shy and gentle person of very independent thought and action, with strong artistic perceptiveness. Being a rationalist and an atheist, she taught him that he must accept responsibility for his own destiny, and especially for his failings in life.That early influence may well have led him to adopt the religious atheistic personal philosophy to which he has adhered since the age of about fifteen. His father was a much more conventional person than his mother, and was awarded the O.B.E. for his success as a Civil Servant.

Peter Mitchell was educated at Queens College, Taunton, and at Jesus college, Cambridge. At Queens he benefited particularly from the influence of the Headmaster, C. L. Wiseman, who was an excellent mathematics teacher and an accomplished amateur musician. The result of the scholarship examination that he took to enter Jesus College Cambridge was so dismally bad that he was only admitted to the University at all on the strength of a personal letter written by C. L. Wiseman. He entered Jesus College just after the commencement of war with Germany in 1939. In Part I of the Natural Sciences Tripos he studied physics, chemistry, physiology, mathematics and biochemistry, and obtained a Class III result. In part II, he studied biochemistry, and obtained a II-I result for his Honours Degree.

He accepted a research post in the Department of Biochemistry, Cambridge, in 1942 at the invitation of J. F. Danielli. He was very fortunate to be Danielli’s only Ph.D. student at that time, and greatly enjoyed and benefited from Danielli’s friendly and unauthoritarian style of research supervision. Danielli introduced him to David Keilin, whom he came to love and respect more than any other scientist of his acquaintance.

He received the degree of Ph.D. in early 1951 for work on the mode of action of penicillin, and held the post of Demonstrator at the Department of Biochemistry, Cambridge, from 1950 to 1955. In 1955 he was invited by Professor Michael Swann to set up and direct a biochemical research unit, called the Chemical Biology Unit, in the Department of Zoology, Edinburgh University, where he was appointed to a Senior Lectureship in 1961, to a Readership in 1962, and where he remained until acute gastric ulcers led to his resignation after a period of leave in 1963.

From 1963 to 1965, he withdrew completely from scientific research, and acted as architect and master of works, directly supervising the restoration of an attractive Regency-fronted Mansion, known as Glynn House, in the beautiful wooded Glynn Valley, near Bodmin, Cornwall – adapting and furnishing a major part of it for use as a research labotatory. In this, he was lucky to receive the enthusiastic support of his fornler research colleague Jennifer Moyle. He and Jennifer Moyle founded a charitable company, known as Glynn Research Ltd., to promote fundamental biological research and finance the work of the Glynn Research Laboratories at Glynn House. The original endowment of about £250,000 was donated about equally by Peter Mitchell and his elder brother Christopher John Mitchell.

In 1965, Peter Mitchell and Jennifer Moyle, with the practical help of one technician, Roy Mitchell (unrelated to Peter Mitchell), and with the administrative help of their company secretary, embarked on the programme of research on chemiosmotic reactions and reaction systems for which the Glynn Research Institute has become known. Since its inception, the Glynn Research Institute has not had sufficient financial resources to employ more than three research workers, including the Research Director, on its permanent staff. He has continued to act as Director of Research at the Glynn Research Institute up to the present time. An acute lack of funds has recently led to the possibility that the Glynn Research Institute may have to close.

Mitchell studied the mitochondrion, the organelle that produces energy for the cell. ATP is made within the mitochondrion by adding a phosphate group to ADP in a process known as oxidative phosphorylation. Mitchell was able to determine how the different enzymes involved in the conversion of ADP to ATP are distributed within the membranes that partition the interior of the mitochondrion. He showed how these enzymes’ arrangement facilitates their use of hydrogen ions as an energy source in the conversion of ADP to ATP.

Peter Mitchell’s 1961 paper introducing the chemiosmotic hypothesis started a revolution which has echoed beyond bioenergetics to all biology, and shaped our understanding of the fundamental mechanisms of biological energy conservation, ion and metabolite transport, bacterial motility, organelle structure and biosynthesis, membrane structure and function, homeostasis, the evolution of the eukaryote cell, and indeed every aspect of life in which these processes play a role. The Nobel Prize for Chemistry in 1978, awarded to Peter Mitchell as the sole recipient, recognized his predominant contribution towards establishing the validity of the chemiosmotic hypothesis, and ipso facto, the long struggle to convince an initially hostile establishment.

NOBEL PRIZE IN CHEMISTRY FOR BIOLOGICAL ENERGY TRANSFER

Mitchell’s research has been carried out within an area of biochemistry often referred to in recent years as ‘bioenergetics’, which is the study of those chemical processes responsible for the energy supply of living cells. Life processes, as all events that involve work, require energy, and it is quite natural that such activities as muscle contraction, nerve conduction, active transport, growth, reproduction, as well as the synthesis of all the substances that are necessary for carrying out and regulating these activities, could not take place without an adequate supply of energy.

It is now well established that the cell is the smallest biological entity capable of handling energy. Common to all living cells is the ability, by means of suitable enzymes, to derive energy from their environment, to convert it into a biologically useful form, and to utilize it for driving various energy requiring processes. Cells of green plants as well as certain bacteria and algae can capture energy by means of chlorophyll directly from sunlight – the ultimate source of energy for all life on Earth – and utilize it, through photosynthesis, to convert carbon dioxide and water into organic compounds. Other cells, including those of all animals and many bacteria, are entirely dependent for their existence on organic compounds which they take up as nutrients from their environment. Through a process called cell respiration, these compounds are oxidized by atmospheric oxygen to carbon dioxide and water.

During both photosynthesis and respiration, energy is conserved in a compound called adenosine triphosphate, abbreviated as ATP. When ATP is split into adenosine diphosphate (ADP) and inorganic phosphate (Pi), a relatively large amount of energy is liberated, which can be utilized, in the presence of specific enzymes, to drive various energy-requiring processes. Thus, ATP may be regarded as the universal ‘energy currency’ of living cells. The processes by which ATP is formed from ADP and Pi during photosynthesis and respiration are usually called ‘photophosphorylation’ and ‘oxidative phosphorylation’, respectively. The two processes have several features in common, both in their enzyme composition – both involve an interaction between oxidizing (electron-transferring) and phosphorylating enzymes – and in their association with cellular membranes. In higher cells, photophosphorylation and oxidative phosphorylation occur in specific membrane-enclosed organelles, chloroplasts and mitochondria, respectively in bacteria, both these processes are associated with the cell membrane.

The above concepts had been broadly outlined by about the beginning of the 1960s, but the exact mechanisms by which electron transfer is coupled to ATP synthesis in oxidative phosphorylation and in photophosphorylation remained unknown. Many hypotheses were formulated, especially with regard to the mechanism of oxidative phosphorylation most of these postulated a direct chemical interaction between oxidizing and phosphorylating enzymes. Despite intensive research in many laboratories, however, no experimental evidence could be obtained for any of these hypotheses. At this stage, in 1961, Mitchell proposed an alternative mechanism for the coupling of electron transfer to ATP synthesis, based on an indirect interaction between oxidizing and phosphorylating enzymes. He suggested that the flow of electrons through the enzymes of the respiratory or photosynthetic electron-transfer chains drives positively charged hydrogen ions, or protons, across the membranes of mitochondria, chloroplasts and bacterial cells. As a result, an electrochemical proton gradient is created across the membrane. The gradient consists of two components: a difference in hydrogen ion concentration, or pH, and a difference in electric potential the two together form what Mitchell calls the ‘protonmotive force’. The synthesis of ATP is driven by a reverse flow of protons down the gradient. Mitchell’s proposal has been called the ‘chemiosmotic theory’.

This theory was first received with scepticism but, over the past 15 years, work in both Mitchell’s and many other laboratories have shown that the basic postulates of his theory are correct. Even though important details of the underlying molecular mechanisms are still unclear, the chemiosmotic theory is now generally accepted as a fundamental principle in bioenergetics. This theory provides a rational basis for future work on the detailed mechanisms of oxidative phosphorylation and photophosphorylation. In addition, this concept of biological power transmission by protonmotive force (or ‘proticity’, as Mitchell has recently began to call it in an analogy with electricity) has already been shown to be applicable to other energy-requiring cellular processes. These include the uptake of nutrients by bacterial cells, cellular and intracellular transport of ions and metabolites, biological heat production, bacterial motion, etc. In addition, the chloroplasts of plants, which harvest the light-energy of the sun, and the mitochondria of animal cells, which are the main converters of energy from respiration, are remarkably like miniaturized solar- and fuel-cell systems. Mitchell’s discoveries are therefore both interesting and potentially valuable, not only for the understanding of biological energy-transfer systems but also in relation to the technology of energy conversion.


4.10: Chemiosmosis - Biology

The advancement of synthetic biology over the past decade has contributed substantially to the growing bioeconomy. A recent report by the National Academies highlighted several areas of advancement that will be needed for further expansion of industrial biotechnology, including new focuses on design, feedstocks, processing, organism development, and tools for testing and measurement more particularly, a focus on expanded chassis and end-to-end design in an effort to move beyond the use of E. coli and S. cerivisiea to organisms better suited to fermentation and production second, continued efforts in systems biology and high-throughput screening with a focus on more rapid techniques that will provide the needed information for moving to larger scale and finally, work to accelerate the building of a holacratic community with collaboration and engagement between the relevant government agencies, industry, academia, and the public.

Letters
Trade-Offs in Improving Biofuel Tolerance Using Combinations of Efflux Pumps

Microbes can be engineered to produce next-generation biofuels however, the accumulation of toxic biofuels can limit yields. Previous studies have shown that efflux pumps can increase biofuel tolerance and improve production. Here, we asked whether expressing multiple pumps in combination could further increase biofuel tolerance. Pump overexpression inhibits cell growth, suggesting a trade-off between biofuel and pump toxicity. With multiple pumps, it is unclear how the fitness landscape is impacted. To address this, we measured tolerance of Escherichia coli to the biojet fuel precursor α-pinene in one-pump and two-pump strains. To support our experiments, we developed a mathematical model describing toxicity due to biofuel and overexpression of pumps. We found that data from one-pump strains can accurately predict the performance of two-pump strains. This result suggests that it may be possible to dramatically reduce the number of experiments required for characterizing the effects of combined biofuel tolerance mechanisms.

Optically Controlled Signal Amplification for DNA Computation
  • Alexander Prokup ,
  • James Hemphill ,
  • Qingyang Liu , and
  • Alexander Deiters*

The hybridization chain reaction (HCR) and fuel–catalyst cycles have been applied to address the problem of signal amplification in DNA-based computation circuits. While they function efficiently, these signal amplifiers cannot be switched ON or OFF quickly and noninvasively. To overcome these limitations, a light-activated initiator strand for the HCR, which enabled fast optical OFF → ON switching, was developed. Similarly, when a light-activated version of the catalyst strand or the inhibitor strand of a fuel–catalyst cycle was applied, the cycle could be optically switched from OFF → ON or ON → OFF, respectively. To move the capabilities of these devices beyond solution-based operations, the components were embedded in agarose gels. Irradiation with customizable light patterns and at different time points demonstrated both spatial and temporal control. The addition of a translator gate enabled a spatially activated signal to travel along a predefined path, akin to a chemical wire. Overall, the addition of small light-cleavable photocaging groups to DNA signal amplification circuits enabled conditional control as well as fast photocontrol of signal amplification.

Directed Evolution of a Panel of Orthogonal T7 RNA Polymerase Variants for in Vivo or in Vitro Synthetic Circuitry

T7 RNA polymerase is the foundation of synthetic biological circuitry both in vivo and in vitro due to its robust and specific control of transcription from its cognate promoter. Here we present the directed evolution of a panel of orthogonal T7 RNA polymerase:promoter pairs that each specifically recognizes a synthetic promoter. These newly described pairs can be used to independently control up to six circuits in parallel.

Probing Yeast Polarity with Acute, Reversible, Optogenetic Inhibition of Protein Function

We recently developed a technique for rapidly and reversibly inhibiting protein function through light-inducible sequestration of proteins away from their normal sites of action. Here, we adapt this method for inducible inactivation of Bem1, a scaffold protein involved in budding yeast polarity. We find that acute inhibition of Bem1 produces profound defects in cell polarization and cell viability that are not observed in bem1Δ. By disrupting Bem1 activity at specific points in the cell cycle, we demonstrate that Bem1 is essential for the establishment of polarity and bud emergence but is dispensable for the growth of an emerged bud. By taking advantage of the reversibility of Bem1 inactivation, we show that pole size scales with cell size, and that this scaling is dependent on the actin cytoskeleton. Our experiments reveal how rapid reversible inactivation of protein function complements traditional genetic approaches. This strategy should be widely applicable to other biological contexts.

Articles
Sequence Design for a Test Tube of Interacting Nucleic Acid Strands

We describe an algorithm for designing the equilibrium base-pairing properties of a test tube of interacting nucleic acid strands. A target test tube is specified as a set of desired “on-target” complexes, each with a target secondary structure and target concentration, and a set of undesired “off-target” complexes, each with vanishing target concentration. Sequence design is performed by optimizing the test tube ensemble defect, corresponding to the concentration of incorrectly paired nucleotides at equilibrium evaluated over the ensemble of the test tube. To reduce the computational cost of accepting or rejecting mutations to a random initial sequence, the structural ensemble of each on-target complex is hierarchically decomposed into a tree of conditional subensembles, yielding a forest of decomposition trees. Candidate sequences are evaluated efficiently at the leaf level of the decomposition forest by estimating the test tube ensemble defect from conditional physical properties calculated over the leaf subensembles. As optimized subsequences are merged toward the root level of the forest, any emergent defects are eliminated via ensemble redecomposition and sequence reoptimization. After successfully merging subsequences to the root level, the exact test tube ensemble defect is calculated for the first time, explicitly checking for the effect of the previously neglected off-target complexes. Any off-target complexes that form at appreciable concentration are hierarchically decomposed, added to the decomposition forest, and actively destabilized during subsequent forest reoptimization. For target test tubes representative of design challenges in the molecular programming and synthetic biology communities, our test tube design algorithm typically succeeds in achieving a normalized test tube ensemble defect ≤1% at a design cost within an order of magnitude of the cost of test tube analysis.

TALENs-Assisted Multiplex Editing for Accelerated Genome Evolution To Improve Yeast Phenotypes
  • Guoqiang Zhang ,
  • Yuping Lin ,
  • Xianni Qi ,
  • Lin Li ,
  • Qinhong Wang* , and
  • Yanhe Ma

Genome editing is an important tool for building novel genotypes with a desired phenotype. However, the fundamental challenge is to rapidly generate desired alterations on a genome-wide scale. Here, we report TALENs (transcription activator-like effector nucleases)-assisted multiplex editing (TAME), based on the interaction of designed TALENs with the DNA sequences between the critical TATA and GC boxes, for generating multiple targeted genomic modifications. Through iterative cycles of TAME to induce abundant semirational indels coupled with efficient screening using a reporter, the targeted fluorescent trait can be continuously and rapidly improved by accumulating multiplex beneficial genetic modifications in the evolving yeast genome. To further evaluate its efficiency, we also demonstrate the application of TAME for significantly improving ethanol tolerance of yeast in a short amount of time. Therefore, TAME is a broadly generalizable platform for accelerated genome evolution to rapidly improve yeast phenotypes.

Enzymatic Menthol Production: One-Pot Approach Using Engineered Escherichia coli
  • Helen S. Toogood* ,
  • Aisling Ní Cheallaigh ,
  • Shirley Tait ,
  • David J. Mansell ,
  • Adrian Jervis ,
  • Antonios Lygidakis ,
  • Luke Humphreys ,
  • Eriko Takano ,
  • John M. Gardiner , and
  • Nigel S. Scrutton*

Menthol isomers are high-value monoterpenoid commodity chemicals, produced naturally by mint plants, Mentha spp. Alternative clean biosynthetic routes to these compounds are commercially attractive. Optimization strategies for biocatalytic terpenoid production are mainly focused on metabolic engineering of the biosynthesis pathway within an expression host. We circumvent this bottleneck by combining pathway assembly techniques with classical biocatalysis methods to engineer and optimize cell-free one-pot biotransformation systems and apply this strategy to the mint biosynthesis pathway. Our approach allows optimization of each pathway enzyme and avoidance of monoterpenoid toxicity issues to the host cell. We have developed a one-pot (bio)synthesis of (1R,2S,5R)-(−)-menthol and (1S,2S,5R)-(+)-neomenthol from pulegone, using recombinant Escherichia coli extracts containing the biosynthetic genes for an “ene”-reductase (NtDBR from Nicotiana tabacum) and two menthone dehydrogenases (MMR and MNMR from Mentha piperita). Our modular engineering strategy allowed each step to be optimized to improve the final production level. Moderate to highly pure menthol (79.1%) and neomenthol (89.9%) were obtained when E. coli strains coexpressed NtDBR with only MMR or MNMR, respectively. This one-pot biocatalytic method allows easier optimization of each enzymatic step and easier modular combination of reactions to ultimately generate libraries of pure compounds for use in high-throughput screening. It will be, therefore, a valuable addition to the arsenal of biocatalysis strategies, especially when applied for (semi)-toxic chemical compounds.

The Dual Characteristics of Light-Induced Cryptochrome 2, Homo-oligomerization and Heterodimerization, for Optogenetic Manipulation in Mammalian Cells
  • Daphne L. Che ,
  • Liting Duan ,
  • Kai Zhang , and
  • Bianxiao Cui*

The photoreceptor cryptochrome 2 (CRY2) has become a powerful optogenetic tool that allows light-inducible manipulation of various signaling pathways and cellular processes in mammalian cells with high spatiotemporal precision and ease of application. However, it has also been shown that the behavior of CRY2 under blue light is complex, as the photoexcited CRY2 can both undergo homo-oligomerization and heterodimerization by binding to its dimerization partner CIB1. To better understand the light-induced CRY2 activities in mammalian cells, this article systematically characterizes CRY2 homo-oligomerization in different cellular compartments, as well as how CRY2 homo-oligomerization and heterodimerization activities affect each other. Quantitative analysis reveals that membrane-bound CRY2 has drastically enhanced oligomerization activity compared to that of its cytoplasmic form. While CRY2 homo-oligomerization and CRY2-CIB1 heterodimerization could happen concomitantly, the presence of certain CIB1 fusion proteins can suppress CRY2 homo-oligomerization. However, the homo-oligomerization of cytoplasmic CRY2 can be significantly intensified by its recruitment to the membrane via interaction with the membrane-bound CIB1. These results contribute to the understanding of the light-inducible CRY2-CRY2 and CRY2-CIB1 interaction systems and can be used as a guide to establish new strategies utilizing the dual optogenetic characteristics of CRY2 to probe cellular processes.

Partitioning Variability of a Compartmentalized In Vitro Transcriptional Thresholding Circuit

Encapsulation of in vitro biochemical reaction circuits into small, cell-sized compartments can result in considerable variations in the dynamical properties of the circuits. As a model system, we here investigate a simple in vitro transcriptional reaction circuit, which generates an ultrasensitive fluorescence response when the concentration of an RNA transcript reaches a preset threshold. The reaction circuit is compartmentalized into spherical water-in-oil microemulsion droplets, and the reaction progress is monitored by fluorescence microscopy. A quantitative statistical analysis of thousands of individual droplets ranging in size from a few up to 20 μm reveals a strong variability in effective RNA production rates, which by computational modeling is traced back to a larger-than-Poisson variability in RNAP activities in the droplets. The noise level in terms of the noise strength (the Fano factor) is strongly dependent on the ratio between transcription templates and polymerases, and increases for higher template concentrations.


1 - CHEMIOSMOTIC ENERGY TRANSDUCTION

This chapter discusses the chemiosmotic theory, the morphology of energy-transducing organelles, and Mitchell's postulates. Although some ATP synthesis is catalyzed by soluble enzyme systems, by far the largest proportion is associated with membrane-bound enzyme complexes that are restricted to a particular class of membrane. These energy-transducing membranes are the plasma membrane of simple prokaryotic cells such as bacteria or blue-green algae, the inner membrane of mitochondria, and the thylakoid membrane of chloroplasts. These membranes have a related evolutionary origin, as chloroplasts and mitochondria are commonly thought to have evolved from a symbiotic relationship between a primitive, non-respiring eukaryotic cell, and an invading prokaryote. Thus, the mechanism of ATP synthesis and ion transport associated with these diverse membranes is sufficiently related, despite the differing natures of their primary energy sources, to form the core of classical energy transduction or bioenergetics. Energy-transducing membranes possess a number of distinguishing features. Each membrane has two distinct types of pump. The nature of the primary pump depends on the energy source used by the membrane in the case of mitochondria or respiring bacteria, an electron-transfer chain catalyses the downhill transfer of electrons from substrates to final acceptors such as O2 and uses this energy to generate a gradient of protons.


Review Questions

Which of the following is not an example of an energy transformation?

  1. Heating up dinner in a microwave
  2. Solar panels at work
  3. Formation of static electricity
  4. None of the above

Which of the following is not true about enzymes?

  1. They are consumed by the reactions they catalyze.
  2. They are usually made of amino acids.
  3. They lower the activation energy of chemical reactions.
  4. Each one is specific to the particular substrate(s) to which it binds.

Energy is stored long-term in the bonds of _____ and used short-term to perform work from a(n) _____ molecule.

  1. ATP : glucose
  2. an anabolic molecule : catabolic molecule
  3. glucose : ATP
  4. a catabolic molecule : anabolic molecule

The energy currency used by cells is _____.

The glucose that enters the glycolysis pathway is split into two molecules of _________.

What do the electrons added to NAD + do?

  1. They become part of a fermentation pathway.
  2. They go to another pathway for ATP production.
  3. They energize the entry of the acetyl group into the citric acid cycle.
  4. They are converted into NADP.
  1. the movement of electrons across the cell membrane
  2. the movement of hydrogen atoms across a mitochondrial membrane
  3. the movement of hydrogen ions across a mitochondrial membrane
  4. the movement of glucose through the cell membrane

Which of the following fermentation methods can occur in animal skeletal muscles?

  1. lactic acid fermentation
  2. alcohol fermentation
  3. mixed acid fermentation
  4. propionic fermentation

The cholesterol synthesized by cells uses which component of the glycolytic pathway as a starting point?

Beta oxidation is ________.

  1. the breakdown of sugars
  2. the assembly of sugars
  3. the breakdown of fatty acids
  4. the removal of amino groups from amino acids

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    Learning about Chemiosmosis and ATP Synthesis with Animations Outside of the Classroom

    Many undergraduate biology courses have begun to implement instructional strategies aimed at increasing student interaction with course material outside of the classroom. Two examples of such practices are introducing students to concepts as preparation prior to instruction, and as conceptual reinforcement after the instructional period. Using a three-group design, we investigate the impact of an animation developed as part of the Virtual Cell Animation Collection on the topic of concentration gradients and their role in the actions of ATP synthase as a means of pre-class preparation or post-class reinforcement compared with a no-intervention control group. Results from seven sections of introductory biology (n = 732) randomized to treatments over two semesters show that students who viewed animation as preparation (d = 0.44, p < 0.001) or as reinforcement (d = 0.53, p < 0.001) both outperformed students in the control group on a follow-up assessment. Direct comparison of the preparation and reinforcement treatments shows no significant difference in student outcomes between the two treatment groups (p = 0.87). Results suggest that while student interaction with animations on the topic of concentration gradients outside of the classroom may lead to greater learning outcomes than the control group, in the traditional lecture-based course the timing of such interactions may not be as important.

    Figures

    Experimental treatment groups as defined…

    Experimental treatment groups as defined by the presence and timing of their interaction…

    Descriptive statistics for mean score…

    Descriptive statistics for mean score on the follow-up assignment by treatment condition. Bars…


    Chemiosmosis

    Chemiosmosis Definition
    Chemiosmosis is when ions move by diffusion across a semi-permeable membrane, such as the membrane inside mitochondria. Ions are molecules with a net electric charge, such as Na+, Cl-, or specifically in chemiosmosis that generates energy, H+.

    chemiosmosis The process by which ATP is produced in the inner membrane of a mitochondrion. The electron transport system transfers protons from the inner compartment to the outer as the protons flow back to the inner compartment, the energy of their movement is used to add phosphate to ADP, forming ATP.

    chemiosmosis
    Process whereby an electrochemical proton gradient (pH plus electric potential) across a membrane is used to drive an energy-requiring process such as ATP synthesis or transport of molecules across a membrane against their concentration gradient also called chemiosmotic coupling. (Figure 16-1) .

    : the movement of hydrogen ions down their electrochemical gradient across a membrane through ATP synthase to generate ATP .

    The process whereby a proton gradient and an electrochemical gradient are generated by electron transport and then used to drive ATP synthesis by oxidative phosphorylation.

    electron transport system oxidative phosphorylation aerobic respiration christae mitochondria .

    is an energy-coupling mechanism that uses energy stored in the form of an H+ gradient across a membrane to drive cellular work.
    In mitochondria, the energy for proton gradient formation comes from exergonic redox reactions, and ATP synthesis is the work performed.

    Figure 8.1.6 shows the movement of protons from the matrix into the space between the inner and outer membranes. This creates a concentration gradient.

    to ATP, and two molecules of NAD (the oxidized form of NAD, or nicotinamide adenine dinucleotide) are reduced to NADH. ATP serves as an energy carrier and can be used to power many cellular processes. The NADH carries high-energy electrons, which can be used to produce more ATP by

    Further information: Oxidative phosphorylation,

    and mitochondrion
    In oxidative phosphorylation, the electrons removed from organic molecules in areas such as the protagon acid cycle are transferred to oxygen and the energy released is used to make ATP.

    In a different approach, the thermosynthesis hypothesis considers the bioenergetic process of

    A cluster of several membrane proteins found in the mitochondrial cristae (and bacterial plasma membrane) that function in

    with adjacent electron transport chains, using the energy of a hydrogen-ion concentration gradient to make ATP.

    White fat insulates the body and reduces heat loss
    Brown fat cells in mitochondrial membrane produce heat
    Mitochondria in other tissue /

    . phosphate is cut loose, ATP becomes ADP (Adenosine diphosphate . Adenosine diphosphate. Adenosine triphosphate (ATP) anabolic. catabolic.

    The potential energy stored in the form of an electrochemical gradient, generated by the pumping of hydrogen ions across biological membranes during


    4.10: Chemiosmosis - Biology

    Chemiosmosis is the diffusion of ions across a selectively-permeable membrane. More specifically, it relates to the generation of ATP by the movement of hydrogen ions across a membrane during cellular respiration.
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    chemiosmosis A process in which a proton gradient across a mitochondrial membrane and ATP synthesis pump metabolites across a
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    Chemiosmosis is central to the metabolism of many types of cells: a methane . In each of these situations, chemiosmosis is the process that allows the cell to .
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    Chemiosmosis is the process of diffusion of ions (usually H+ ions, also known as . As in osmosis, chemiosmosis leads to a concentration gradient of the diffusing .
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    Chemiosmosis is the diffusion of ions across a membrane. . The generation of ATP by chemiosmosis occurs in chloroplasts and mitochondria as .
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    1. Mitochondrial Chemiosmosis--- The complete breakdown of . The Main Point: Chemiosmosis is the diffusion of ions across a membrane. .
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    Animation illustrating the development of proton motive force as a result of chemiosmosis. . ATP production by chemiosmosis during aerobic respiration. .
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    Chemiosmosis is the diffusion of ions across a selectively-permeable membrane. . In all cells, chemiosmosis involves the proton-motive force (PMF) in some step. .
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    Chemiosmosis. Energy yield for aerobic respiration. Overview of photosynthesis . chemiosmosis. in 1961 to describe the way in which . chemiosmosis .
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    Chemiosmosis. ATP is produced in the chloroplast by Chemiosmosis. Chemiosmosis requires a phospholipid bilayer, a proton pump, protons and ATPase. .
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    Cristae (singular crista) are the internal compartments formed by the inner . As a result, chemiosmosis occurs, producing ATP from ADP and a phosphate group .
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    A plant that uses the Calvin cycle for the initial steps that incorporate CO2 . The set of reactions by which some . chemiosmosis (kee-mee-os-moh-sis) .
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    Encyclopedia article about Chemiosmosis. Information about Chemiosmosis in the Columbia Encyclopedia, Computer Desktop Encyclopedia, computing dictionary.
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    posted to chemiosmosis coupling localised pmf by dbk to the group streptomyces . posted to chemiosmosis methods pmf by dbk to the group streptomyces on 2004-11 .
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    Includes illustrated information on the nature of light, the chemistry of . Chemiosmosis as it operates in photophosphorylation within a chloroplast. .
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    . in chemiosmosis? 23. How many ATP molecules are produced in chemiosmosis? . Aerobic Anaerobic Cellular respiration Chemiosmosis Citric acid cycle Electron .
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    Glucose contains energy that can be . The electron transport system and chemiosmosis . Via chemiosmosis, ATP is produced. Reaction types. Dehydrogenation .
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    Text Preview

    When photons are absorbed, the electrons in the reaction centers are excited to higher energy levels, allowing them to be transferred to electron acceptor molecules. As electrons flow from molecules with low affinities for electrons to molecules with higher affinities for electrons, energy is released. The released energy is used to pump protons into the lumen. This process stores the energy in a proton gradient.

    Every time a proton is transported into the lumen, a positive charge is transported. The unequal distribution of charges creates an electrical potential across the thylakoid membrane. The unequal distribution of charges as well as the proton concentration gradient creates the proton-motive force. The unequal distribution of protons also causes the pH of the lumen to be several pH units lower than that of the surrounding stroma.

    Protons are only allowed to move out of the lumen through special channels in the chloroplast&rsquos ATP synthase enzyme. As the protons flow through ATP synthase, they drive conformational changes in the enzyme that synthesize ATP from ADP and phosphate. This process is analogous to ATP synthesis in the mitochondria, where protons that were pumped out of the mitochondrial matrix flow back through ATP synthase, and ATP is made. The chemiosmotic model for ATP synthesis describes ATP synthesis in both the mitochondria and in chloroplasts.

    Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education


    An Epiphany about Chemiosmosis

    Chemiosmosis is not an inspiring word to a poet. Through a long series of administrative confusions and a perceived lack of science credit, I was pushed to take another science class my senior year. I remembered liking biology in freshman year, and I realized that AP Biology would help my understanding of environmental science. Three weeks into the school year, I entered the class, woefully behind in reading and missing labs and assessments. I lived my life from between the pages of Campbell's Biology, 7th edition, and I regretted every moment spent studying metabolic pathways and dynein arms.

    But then I came to chemiosmosis, the last process in cellular respiration. I traced the diagram in the book, following the H+ ions across the inner mitochondrial membrane with one finger, pulling the electrons through the proteins within the membrane. Following the electron transport chain, H+ travels across the membrane, forming a proton gradient. Chemiosmosis describes the process in which H+ diffuses back across the membrane through ATP synthase, an enzyme that phosphorylates ADP and creates ATP, the energy "currency" for the cell.

    I sat there, tracing over and over, talking to the proteins and H+ ions, waiting until the information filtered into my brain. Suddenly, my finger stopped and I looked up to where my face was reflected in the dark window. My eyebrows were almost to my hairline. The cycle was genius chemiosmosis sang poetry.

    Each protein, electron, and oxygen molecule builds relationships with other molecules. But these alliances constantly change, based on the varying chemical ingredients of each molecule and its position in relation to the other components of the cell. They are just like humans, constantly bumping and moving, attracted by certain members, passing through relationships, but all working toward a common goal: the formation of ATP. The cycle works perfectly, and it alarmed me, shaking my disinterest toward biology.

    Chemiosmosis swelled away from the molecular level until it encompassed the entire world. The relationships formed at the molecular level fueled my world, from the fingers that traced the H+ ions to the ATP that allowed my heart to beat. One diagram showed the completeness of biology, crafted as carefully as any poem. Biology was no longer about memorization, but about connections and relationships. Chemiosmosis became the stained glass window in my cathedral of biology, the stunning piece that inspired a deeper understanding.

    Biology tempts me now, drawing me from my beloved Vergil lines and essays on Shakespeare, and I crave understanding of cellular respiration, photosynthesis, and evolution. My questioning brain found a niche, where some queries are answerable and others remain mysteries biology captivates my intellect, all because of one diagram, one explanation, one cycle of chemiosmosis.


    Watch the video: Chemiosmosis explained (July 2022).


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