Cellular Energetics

10 Key excerpts on "Cellular Energetics"

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  eBook - ePub

  Introduction to Modern Biophysics

  • Mohammad Ashrafuzzaman(Author)
  • 2023(Publication Date)
  • CRC Press

    (Publisher)

  5 Biochemical Energetics

  DOI: 10.1201/9781003287780-5

  Biological processes run mainly on energy. Oxidation of glucose yields a specific amount of biochemical energy. Energetic changes in fluctuating chemical structural states happen due to intra and inter chemicals interactions occurring continuously at different parts of biological systems. Chemical energetics, occurring among monomer/dimer/multimer transformations and interactions involve bond, electrostatic, and van der Waals energies. This energetic process and associated fluctuations in energies are continuously dealt with by localized structures at different active, functional, and transport-associated parts and compartments in biology. ATP synthesis is itself an energetic process, which utilizes energy originating from various catabolic mechanisms, including cellular respiration, beta-oxidation, and ketosis. Signal transduction, DNA and RNA synthesis, muscle contraction, brain function, etc. cost ATPs. Addressing biochemical energetics thus appears to be a key phenomenon for understanding biology.

  5.1 Fundamentals of Biochemical Energies

  Our body gets energy through the oxidative reaction of glucose (C6 H12 O6 ) as follows:

  C 6

  H 12

  O 6

  + 6

  O 2

  → 6 C

  O 2

  + 6

  H 2

  O + 670   k c a l / m o l  

  (5.1)

  The oxidation of glucose yields 670 kcal of energy for every mole of glucose oxidized. The main source of energy for general cellular metabolism is glucose, which gets catabolized in the following three successive processes in order to produce adenosine triphosphate (ATP):

  • glycolysis,
  • tricarboxylic acid cycle (TCA or Krebs cycle), and finally
  • oxidative phosphorylation

  In the first process, glucose gets converted into pyruvate and produces a low amount of ATP. Pyruvate then gets converted into acetyl coenzyme A (acetyl-CoA) and enters the tricarboxylic acid (TCA) cycle, enabling the production of NADH. Finally, the respiratory chain complexes use NADH in order to generate a proton gradient across the inner mitochondrial membrane, necessary for producing large amounts of ATP by mitochondrial ATP synthase. In addition to these explained processes, it is to be mentioned that acetyl-CoA can also be generated by the catabolism of lipids and proteins, which indirectly participate in determining cellular energy state(s) through contributing to the ATP synthesis process. The majority of ATP synthesis is known to occur in cellular respiration within the mitochondrial matrix, generating approximately 29–32 ATP molecules per 1 oxidized glucose molecule (Flurkey, 2010 ; Dunn and Grider, 2022 ); some textbooks estimate the production of a lower number of ATP molecules (Nelson and Cox, 2004 ; Nicholson, 2001 ; Voet et al., 2002

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  eBook - ePub

  Guide to Biochemistry

  • James C. Blackstock(Author)
  • 2014(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  CHAPTER 10

  Principles of cellular metabolism

  Publisher Summary

  This chapter explains the principles of cellular metabolism. Living cells require energy. The ultimate source of energy is the thermonuclear fusion of hydrogen atoms to form helium that occurs at the surface of the sun. Cycles such as the nitrogen cycle feature prominently in biological systems. These cycles involve a series of chemical reactions in which the initial reactant is regenerated, but a valuable material is simultaneously produced and becomes available to cells. The study of the energetic of any system is described as thermodynamics, the principles of which were elucidated from the quantitative analysis of energy transformations in simpler physical and chemical systems. A thermodynamically favorable reaction may be linked to an unfavorable reaction so that the free energy liberated may be employed to drive the energy-consuming reaction. The major chemical link in cells between exergonic and endergonic reactions is ATP. A metabolic pathway may be defined as a sequence of coupled enzyme-catalysed reactions. The chapter further describes intracellular control of metabolism and extracellular control of metabolism.

  10.1 Biological energetics

  Living cells require energy. The ultimate source of energy is the thermonuclear fusion of hydrogen atoms to form helium which occurs at the surface of the sun according to the equation:

  C

  C o

  =

  1

  (

  1 + k

  C o

  t

  )

  4H → 1He + 2 positrons + energy

  (a positron is a particle which has the same mass as an electron but has a positive charge). The energy is transported to Earth as sunlight (light energy) which is converted into chemical energy by green plants and certain microorganisms by the process of photosynthesis (Chapter 14 ). The chemical energy is stored primarily in carbohydrates synthesized by the reduction of atmospheric carbon dioxide. Also, oxygen is produced from water as a by-product and released into the atmosphere. These products of photosynthesis are vital for aerobic organisms which do not contain the necessary molecular apparatus for the above transformations of energy. Such organisms obtain their energy by utilizing molecular oxygen to oxidize energy-rich plant products. This process called respiration produces amongst other products, carbon dioxide which is returned to the atmosphere to be subsequently utilized in photosynthesis. This cycle of events is called the carbon cycle (Figure 10.1

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  Concepts of Biology

  • Samantha Fowler, Rebecca Roush, James Wise(Authors)
  • 2016(Publication Date)
  • Openstax

    (Publisher)

  From where, and in what form, does this energy come? How do living cells obtain energy, and how do they use it? This chapter will discuss different forms of energy and the physical laws that govern energy transfer. This chapter will also describe how cells use energy and replenish it, and how chemical reactions in the cell are performed with great efficiency. Chapter 4 | How Cells Obtain Energy 91 4.1 | Energy and Metabolism By the end of this section, you will be able to: • Explain what metabolic pathways are • State the first and second laws of thermodynamics • Explain the difference between kinetic and potential energy • Describe endergonic and exergonic reactions • Discuss how enzymes function as molecular catalysts Scientists use the term bioenergetics to describe the concept of energy flow (Figure 4.2) through living systems, such as cells. Cellular processes such as the building and breaking down of complex molecules occur through stepwise chemical reactions. Some of these chemical reactions are spontaneous and release energy, whereas others require energy to proceed. Just as living things must continually consume food to replenish their energy supplies, cells must continually produce more energy to replenish that used by the many energy-requiring chemical reactions that constantly take place. Together, all of the chemical reactions that take place inside cells, including those that consume or generate energy, are referred to as the cell’s metabolism. Figure 4.2 Ultimately, most life forms get their energy from the sun. Plants use photosynthesis to capture sunlight, and herbivores eat the plants to obtain energy. Carnivores eat the herbivores, and eventual decomposition of plant and animal material contributes to the nutrient pool. Metabolic Pathways Consider the metabolism of sugar. This is a classic example of one of the many cellular processes that use and produce energy.

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  eBook - ePub

  Biomolecules

  From Genes to Proteins

  • Shikha Kaushik, Anju Singh(Authors)
  • 2023(Publication Date)
  • De Gruyter

    (Publisher)

  Chapter 4  Concept of Energy in Biosystems

  The highly structured and organized nature of living systems is perceptible and astonishing. Growth, development, and metabolism are some of the fundamental processes that occur in living organisms, and the role of energy is fundamental to all these biological processes. The survival of any living organism depends on energy transformations, that is, the exchange of energy within and without a particular system. The fundamental matter in bioenergetics, that is, the study of energy relationships and conversions in living organisms, signifies the way by which energy from fuel metabolism or by capturing light is coupled to the energy-requiring reactions occurring in the cell. Muscular contraction, synthetic reactions, and active transport are some of the important processes that get energy when linked or coupled with some energy-releasing reactions (exergonic reactions). In all organisms (autotrophic and heterotrophic), ATP (adenosine triphosphate) plays an important role in transferring energy from the exergonic to the endergonic reactions. ATP is called a high-energy phosphate compound and is produced by living organisms via oxidative phosphorylation. The terminal phosphate linkage in ATP is relatively weak; when broken, it yields adenosine monophosphate (AMP) and inorganic phosphate and releases a large amount of energy. An organism’s stockpile of ATP is used by the cells to perform different activities to sustain life, and energy released from rearrangement of bonds within molecules is utilized to power all biological processes in every organism.

  Bioenergetics or biochemical thermodynamics deals with the transformations, exchange, requirements, and processing of energy within living systems. It also focuses on how cells transfer energy. Some of the essential biological processes such as biosynthesis of nucleic acids and other biomolecules are not thermodynamically favored under provided conditions, as they require an input of energy. They can proceed if coupled with energy-releasing processes. So, it endows with the answer why some reactions may occur while others do not.

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  Microbial Process Development

  • H W Doelle(Author)
  • 1994(Publication Date)
  • WSPC

    (Publisher)

  CHAPTER 6 C e l l T h e r m o d y n a m i c s 1. Concept of thermodynamics of biological systems One of the most fundamental properties of l i v i n g c e l l systems is their a b i l i t y to u t i l i z e and transform energy. This energy occurs in a number of forms: Mechanical Energy is developed during cellular movement, beating of flagella, reorganization of intracellular structures such as mitochondria, and alteration of c e l l shape; Electrical Energy is produced when electrons move from one place to another, usually expressed as a flow of current between two points due to a difference in voltage; Electromagnetic Energy occurs in the form of radiation, and in biology the most significant is that from visible or near-visible light, such as radiation from the sun for photosynthet-ic organisms. Some organisms release energy and glow, which i s referred to as bioluminescence. They produce light energy. Chemical Energy is the energy that can be released from chemical reactions; Thermal Energy or heat is produced as part of the normal energy transformation processes and occurs as waste energy released into the surroundings; Atomic Energy i s contained within the structure of atoms themselves and is released in the form of atomic radiation, which can not be u t i l i z e d by living organisms. Since growth can be defined as the orderly increase of a l l chemical components, i t is the chemical form of energy which is of greatest importance for the understanding of microbial growth and metabolism. Microbial metabolism consists of thousands of individual chemical and enzyme-catalyzed chemical reactions. These chemical reactions in l i v i n g organisms occur in characteristi-cally organized sequences, called metabolic pathways. There are two main types of metabolic pathways: (a) pathways which lead from large (low oxidative state) to smaller molecules (high oxidative state), which are called catabolic pathways or catabolism. 91

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  Energy And Life

  • John Wrigglesworth(Author)
  • 1997(Publication Date)
  • CRC Press

    (Publisher)

  1 Introduction to Bioenergetics Two CONDITIO NS NECESSARY FOR LIFE • Mechanism(s) for the control of energy flow • Systems for informa-tion storage and transmiss ion 1.1 Life and ener gy Energy flow is essential for life and bioenergetics describes how living systems capture, transform and use energy. Almost immediately we meet a problem which turns most students away from the subject. The concept of energy is not an easy one. Definitions are very abstrac t, 'the capa city to do work', 'the energy of an object by virtue of its position', the 'rest-mass energy' of an object. In fact we real ly have no knowledg e of what energy is. Another awkward fact is tha t energy also seems to exist in many different forms. We can speak of potential energy, kinetic energy, heat energy, elec-trical energy, chemical energy, radiant energy, nuclear energy, and ev en 'information ' en ergy. Certain observational facts or laws, the laws of thermodynamics, allow us to do various calculations about energy and energy transforma-tions but these do not lead us any closer to the abstract thing tha t is called energy. Nevertheless, the conti nuous flow of energy through organisms is required for life. A second requirement for life, which is probably easier to imagine, is some method of storing information and passing the knowledge from one generation to the next. We know how this works quite well. The information is stored in the linear sequence of bases in deoxyribonucleic acid (DNA) in the form of the genetic code. Replication of DNA occurs to transmit the informatio n from one generation to the next. The production of ribonucleic acid (RNA) (transcription) and protein (translatio n) allows this informatio n to be used for the essential functions of life. Nevertheless, althoug h an information system is necessary for life it is not sufficient on its own. For example, we do not think of viruses as living systems although they have a very efficient informatio n sto-rage system.

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  Karp's Cell Biology

  • Gerald Karp, Janet Iwasa, Wallace Marshall(Authors)
  • 2018(Publication Date)
  • Wiley

    (Publisher)

  Thus, the farther a reaction is kept from its equilibrium state, the less its capacity to do work is lost to the increase in entropy. Cellular metabolism is essentially nonequilibrium metabolism; that is, it is characterized by non- equilibrium ratios of products to reactants. This does not mean that some reactions do not occur at or near equilibrium within cells. In fact, many of the reactions of a metabolic pathway may be near equilibrium (see Figure 3.25). However, at least one and often several reactions in a pathway are poised far from equilib- rium, making them essentially irreversible. These are the reac- tions that keep the pathway going in a single direction. These are also the reactions that are subject to cellular regulation because the flow of materials through the entire pathway can be greatly increased or decreased by stimulating or inhibiting the activity of the enzymes that catalyze these reactions. 3.5 • Enzymes as Biological Catalysts 95 The basic principles of thermodynamics were formulated using nonliving, closed systems (no exchange of matter between the system and its surroundings) under reversible equilibrium conditions. The unique features of cellular metabolism require a different perspective. Cellular metabolism can maintain itself at irreversible, nonequilibrium conditions because unlike the envi- ronment within a test tube, the cell is an open system. Materials and energy are continually flowing into the cell from the blood- stream or culture medium. The extent of this input into cells from the outside becomes apparent if you simply hold your breath. We depend from minute to minute on an external source of oxygen because oxygen is a very important reactant in cellular metabolism. The continual flow of oxygen and other materials into and out of cells allows cellular metabolism to exist in a steady state (FIGURE 3.7).

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  Visualizing Microbiology

  • Rodney P. Anderson, Linda Young, Kim R. Finer(Authors)
  • 2020(Publication Date)
  • Wiley

    (Publisher)

  Basic Energy Principles Energy exists in two principal forms: kinetic and potential. Kinetic energy is the energy of motion. Potential energy is stored energy associated with position. It may be the energy of a chemical bond, a concentration gradient, or a charge imbal- ance. Potential and kinetic energy are interconvertible. Cells require a continuous supply of energy to live. The energy must be in usable quantities and of a particular type or quality. Chemical energy, such as that provided by the compound ade- nosine triphosphate (ATP), is considered a high-quality form of energy because it is easily converted to other energy forms and can be used to drive almost any cellular process. For example, cells can transform ATP into the mechanical motion of a flagellum or the heat needed to maintain a normal body temperature. (ATP and its role in cellular metabolism are discussed in Section 9.2.) Heat energy is the random motion of molecules. In con- trast to chemical energy, heat is a low-quality form of kinetic energy that cannot be converted into other forms of energy by physiological processes. For this and other reasons, heat is not used to drive cellular processes. Energy and Chemical Reactions Chemical reactions, including metabolic reactions, either release energy or require an input of energy. Reactions that release energy are exergonic reactions, and reactions that require the addition of energy are endergonic reactions (Figure 9.1). metabolism The sum total of the chemical reactions necessary for the life of an organism. adenosine triphosphate (ATP) A molecule composed of adeno- sine and three adjacent phosphate groups that is able to release 7.3 kcal/mol of energy when hydrolyzed. Put It Together Review the section Basic Energy Principles, and answer this question. How does the potential energy of the reactant change compared to the product in the course of an endergonic reaction? a. It increases and then decreases.

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  Physics and Biology

  • M Volkenstein(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  CHAPTER 8 Cellular Biophysics and Bioenergetics Studies performed at the molecular level reveal the physico-chemical fundamentals of the most important biological phenom-ena—heredity, variability, and enzymatic catalysis. We begin by ac-quiring an understanding of the molecular-biological laws, which we then use to approach a higher level of biological organization— the cell. Let us consider two very general problems: first, the regulation of gene action, which determines ontogenic development, the differ-entiation of the cells, morphogenesis, and carcinogenesis; second, the subject of bioenergetics, the storage of the chemical energy in the cell and its use for various kinds of work. The whole multicellular organism is programmed genetically; the genetic information contained in DNA determines the pattern of development of the organism and its hereditary characteristics. Evi-dently, this information is already contained in the initial embryonic cell, the zygote, which is the result of the union of the maternal ovicell and the paternal spermatozoon. The organism arises as the result of division of the zygote and subsequent cells, and their differ-entiation and specialization. During every division of the cell, the genetic material—chromosomes and DNA—is doubled. This means that every specialized cell contains the complete initial set of genes. However, in a given cell only the proteins responsible for its specialized behavior are synthesized; but the set of genes contained in the zygote and in all other cells serves as the program of synthesis of all proteins in all the organism's cells. Hence, the only genes 73 74 Chapter 8 working in a given cell are those that determine the synthesis of a small fraction of proteins necessary for the cell's functioning; the other genes are suppressed or repressed. The genetic program is regulated. This reasoning was proved by the experiments on plants made by Stewart and later Butenko.

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  Bioenergetics at a Glance

  An Illustrated Introduction

  • D. A. Harris(Author)
  • 2009(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  This restriction is, however, too severe. The role of ion gradients, championed by Peter Mitchell, requires there to be a close inter- relationship between such gradients and both redox reactions and ATP hydrolysis. Thus there are, included in the present text, ana- logous systems-generation of ion gradients by ATP hydrolysis or by light-and other possible uses of ion gradients-in transport, heat generation or motion. Similarly, present day bioenergetics is the product of a long evolutionary history, and, in particular, the remarkable endosymbiotic origin of mitochondria and chloroplasts; this too is covered. I have reluctantly, but conventionally drawn the line above ATP-driven motility systems such as muscle and eukar- yotic tlagellae. This is a good time to write a textbook on bioenergetics. Advances in molecular biology over the past 10 years have allowed us to move away from 'black boxes' and 'squiggles' (-) and give our ideas of mechanism a structural basis-still oversimplified in many cases, 6 but at least lending an air of clarity. I have thus attempted, wherever possible, to combine ideas of structure and mechanism-to provide the framework without losing track of the vitality. Bioenergetics at a Glance is structured as a modular text, with topics discussed in one-or occasionally more-double page spreads or modules. Apart from a certain arbitrariness in the choice of boundaries, the major drawback to this approach is the inability to explore controversies in any depth. In such cases, I regret any oversimplifications, or overextrapolation on my part, which may have resulted. I justify them in the aim of clarifying the underlying principles. The advantages of this structure lie in its ease of use. Topics for study, and for revision, are easily identified and can be studied with little reference to the rest of the text (except perhaps as a glossary).

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