Secondary Active Transport

8 Key excerpts on "Secondary Active Transport"

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  eBook - ePub

  Principles of Animal Nutrition

  • Guoyao Wu(Author)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  Active transport refers to the energy-dependent, carrier protein–mediated movement of substances through the biological membrane against their concentration or electrochemical gradients. An example of active transport is the uptake of glutamine from the plasma (0.5–1 mM) into skeletal muscle (10–20 mM) by transporter N (Xue et al. 2010). The energy required for active transport is almost exclusively provided by ATP hydrolysis.

  Secondary Active Transport refers to a form of active transport where a substance crossing the biological membrane is coupled with the movement of an ion (typically Na+ or H+ ) down its electrochemical potential (Friedman 2008). Secondary Active Transport requires a carrier protein and is commonly referred to as ion-coupled transport. On the basis of the direction of movement of coupled solutes, transporters of Secondary Active Transport are known as either symporters (cotransporters) for the same direction of solute movement or antiporters (exchangers or counter-transporters) for the opposite direction of solute movement. An example of Secondary Active Transport is the transport of glucose from the lumen of the small intestine into the enterocyte through sodium–glucose-linked transporter-1 (SGLT1; a symporter) on the apical membrane (brush-border membrane) (Boron 2004). SGLT1 utilizes the co-movement of Na+ down its electrochemical gradient to drive the complete uptake of glucose from the intestinal lumen. In contrast, the Na+ /H+ exchanger, which plays a major role in regulating the intracellular pH and Na+ homeostasis, is an antiporter. Secondary Active Transport does not directly require energy (ATP, GTP, or UTP) (Cooper and Hausman 2016).

  Overview of the Animal System

  An animal is composed of nine systems (nervous, digestive, circulatory, musculoskeletal, respiratory, urinary, reproductive, endocrine, and immune systems) and five sense organs (Dyce et al. 1996). Utilization of dietary nutrients by animals involves the cooperation of all the organs in the body. For example, the nervous system controls the food intake and behavior of animals; the digestive system is required for the digestion and absorption of enteral nutrients in diets; the circulatory system is needed for the transport of absorbed nutrients from the stomach and intestine into the general circulation; the respiratory system is responsible for the supply of oxygen to oxidize fatty acids, glucose, and AAs into CO2 and water; the endocrine system regulates nutrient metabolism under physiological and pathological conditions; the immune system protects the animal from infection and ensures a healthy state; the urinary system excretes metabolites from the body; the musculoskeletal system provides the structure, support, and movement (e.g., walking, chewing, swallowing, and breathing) of the organism, with skeletal muscle being the major component of growth (Davis et al. 2002; Field et al. 2002; Scanes 2009); and the reproductive system ensures the continuous propagation of the animal species (Guyton and Hall 2000). Thus, it is important for nutritionists to understand the complexity and interactions of all the anatomical systems in animals. Figure

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  eBook - ePub

  Advanced Drug Delivery

  • Ashim Mitra, Chi H. Lee, Kun Cheng(Authors)
  • 2013(Publication Date)
  • Wiley

    (Publisher)

  Active transport results in the accumulation of a solute on one side of the membrane and often against its electrochemical gradient. It occurs only when solute accumulation is coupled with the exergonic process directly or indirectly [4]. During the transport process, energy sources, such as adenosine triiphosphate (ATP), electron transport, or an electrochemical gradient of another ion, are used to drive ions or molecules against their electrochemical potential gradients [4]. The active transport process maintains membrane potential and ion gradients, storage of energy for secondary transporters, and pH regulation inside the cell [4].

  In primary active transport, solute accumulation is directly coupled with the exergonic reaction (conversion of ATP to adenosine triiphosphate (ADP) + Pi) [4]. Secondary Active Transport occurs when uphill transport of one solute is coupled with the downhill flow of another solute that was originally pumped uphill flow by primary active transport.

  An example of the primary active transporter is the Na+ K+ ATPase in the mammalian cells that is energized by ATP [4]. Animal cells maintain a lower concentration of Na+ and a higher concentration of K+ intracellularly than are found in extracellular fluid. This concentration difference is established and maintained by primary active transport systems in the plasma membrane. The process is mediated by the enzyme Na+ K+ ATPase that couples the breakdown of ATP with the simultaneous and electrogenic movements of both Na+ and K+ against their concentration gradients (i.e., three Na+ ions move outward for every two K+ ions that move inward) [4].

  In animal cells, the differences in cytosolic and extracellular concentrations of Na+ and K+ are maintained by active transport via Na+ K+ ATPase, and the generated Na+ gradient is used as an energy source by a variety of symport and antiport systems [4]. The Na+ K+ ATPase shows specific distribution patterns on the animal cell surface. A few primary active transporters, such as MDR1, MRP2, MRP4, and BCRP in the epithelial membrane, and MRP1, MRP3, MRP4, and MRP5 in the basolateral membrane, are shown in Figure 1.1

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  The Movement Of Molecules Across Cell Membranes

  • Wes Stein(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  C H A P T E R 6 The Primary Active Transport Systems 6.1 Criteria for Distinguishing between Primary and Secondary Active Transport Systems A simple yet sufficient criterion of the existence of an active transport system is that the following condition b e satisfied: A net flux of the permeant must occur in a direction opposite to that of the electrochemical gradient of the transferred species (Section 2 . 7 ) . In Chapter 5 w e saw that many active transports arise as a result of the co-transport of a metabolite together with sodium ions. T h e linking of the fluxes of the metabolite and the sodium ions results from the requirement that both these species must be attached to the mobile membrane carrier if transport is to occur. Thus the force driving the flux of sodium ions (the electrochemical gradient of sodium) indirectly drives by co-transport the flux of metabolite. W e have seen, too (Section 5 . 5 ) , that by counter-transport the active transport of a third species can b e linked by two stages with the electrochemical gradient of sodium ions. It is conceivable that all active transport in a cell might occur by such secondary and tertiary transports, the fundamental concentration gradient arising per-haps from the continual intracellular depletion of some cell constituent by metabolic activity. L e t us consider how we could distinguish between this situation and a true case of primary transport. W e begin by considering the possible forces that can drive a net flux. In Section 2.8 we saw how it was possible to consider Ji the flux of the ith component as resulting from ( 1 ) the electrochemical gradient in i i t s e l f : — Δ /Λ ί? · or ( 2 ) an interaction with the flux J } of some other com-ponent or ( 3 ) the action of some chemical reaction J r . Formally, we can write η Ji = Ra Αμΐ + ^RijJj + RirJr (6 -1) .7 = 0 207 208 6. THE PRIMARY ACTIVE TRANSPORT SYSTEMS where the interaction coefficients are the respective terms R.

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  Transport And Diffusion Across Cell Membranes

  • Wilfred Stein(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  CHAPTER 5 The Cotransport Systems: Two Substrates That Are Carried on a Single Transporter 5.1. ACTIVE TRANSPORT AND PHYSIOLOGY It is a fundamental characteristic of living cells that their content of ions and small molecules is quite different from that of their environment. The cell accumulates certain metabolites, often to levels of concentration far above those present in the environment. The cell can also rid itself of substances present at high levels in the environment and capable of penetrating the cell membrane. This phenomenon—the accumulation of metabolites within the cell or the exclusion of others from the cell, in the face of concentration gradients of the transported metabolite—is known as active transport. The elucidation of how such active transport is achieved by the organism is one of the triumphs of modern physiology. In this chapter we shall consider one type of active transport in which transport of one metabolite is coupled to the simultaneous transport of another. In the next chapter we shall discuss another type of active transport in which transport of the metabolite is coupled to chemical work, the splitting of ATP. We term these, following Mitchell (1966, 1977), osmotic-osmotic coupling and chemiosmotic coupling, respectively. We have studied up to now in this volume how ions or molecules move down their concentration gradients by simple diffusion, by movement through channels, or by facilitated diffusion on a membrane carrier. We also considered briefly countertransport in which an ion or metabolite 363 364 5. The Cotransport Systems is pumped up its concentration gradient in apparent violation of the second law of thermodynamics! We shall see that it is the fundamental property of the membrane carriers—that they can exist in two confor-mations, with their substrate-binding sites facing either one side of the membrane or the other—that is used by all active transport systems to bring about transport against a concentration gradient.

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  A Modern Course in Transport Phenomena

  • David C. Venerus, Hans Christian Öttinger(Authors)
  • 2018(Publication Date)
  • Cambridge University Press

    (Publisher)

  [Hint: make the realistic assumption that molecular motors work at close to 100 % efficiency.] 24.2 Active Transport: Irreversible Thermodynamics Throughout this book, we have examined a wide range of phenomena involv-ing fluxes of momentum, energy, and mass that are driven by forces resulting 426 Transport in Biological Systems from gradients of velocity, temperature, and concentration. In Chapter 6 , we learned that, to ensure nonnegative entropy production, the direction of the flux coincided with the direction of minus the gradient creating the force. For example, heat is transported from regions of high temperature to re-gions of low temperature, and species mass is transported from regions of high concentration to regions of low concentration. Is it possible for mass to be transferred from regions of low concentration to regions of high concen-tration? Fortunately, for all living things, the answer is yes, and it occurs because of what is known as active transport . Active transport is the transport of mass from regions of low concentra-tion regions of to high concentration made possible by a coupling of diffusive transport and chemical reaction. This statement might appear to be at odds with two important concepts from Chapter 6 : the requirement for nonneg-ative entropy production (violation of the second law of thermodynamics); and the coupling of force–flux pairs having different tensorial orders is not allowed (violation of the Curie principle). In this section, these issues will be addressed as we examine an example of active transport that occurs within biological cells. 4 The key to resolving the apparent violation of the Curie principle is that active transport occurs at cell membranes , which can be treated as interfaces. Cells are separated from the extracellular matrix by membranes, and also organelles within cells (such as mitochondria and vacuoles) are separated from the surrounding cytosol by membranes.

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  Intestinal Absorption of Metal Ions, Trace Elements and Radionuclides

  • S. C. Skoryna, D. Waldron-Edward, S. C. Skoryna, D. Waldron-Edward(Authors)
  • 2013(Publication Date)
  • Pergamon

    (Publisher)

  It is evident that in any animal cell which subserves the function of translocation, the occurrence of some form of cytoplasmic streaming will transport and stir intracellular substrate. Although the occurrence of any orderly movement of the intracellular contents will require the expen-diture of energy and must ultimately add to the metabolic cost of translocation, Ewart has calculated that the energy expended in sustaining protoplasmic streaming must be relatively small. (48) The occurrence of such a process in absorbing cells would serve as yet another example of the wide and fascinating variety of phenomena which challenge workers in the fields of biological transport and intestinal absorption. The response of the investigator to this challenge is to direct his thoughts, ingenuity and efforts towards devising experimental procedures to test his views of the phenomenon. At least one outcome of such experiments can be predicted; many more problems will arise, each yet another challenge to the inves-tigator. Summary 1. A description is given of the properties of some model systems for the transcellular active transport ('translocation') of material across a single layer of epithelial cells. 2. The functioning of the models depends upon the occurrence of solute ('substrate') pumping across the bordering membranes of a unit cell, the membranes being also leaky to the substrate. Two types of system are specified. In one sort the limiting membranes of the unit cell are furnished with 'pumps' which move substrate into the cell so that the intra-cellular electrochemical potential of the substrate is maintained at a value greater than that outside and translocation is achieved by the movement of substrate passively out of the cell down leaks.

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  Medical Biochemistry

  • Gustavo Blanco, Antonio Blanco(Authors)
  • 2017(Publication Date)
  • Academic Press

    (Publisher)

  Class P transporters include several ion transport ATPases. Class V or proton pumps are found in lysosomes and the plasma membrane of some cells. Class F comprises the ATP synthase of the mitochondrial inner membrane. Class ABC groups a family of proteins that move carbohydrates, lipids, peptides, biliary salts, and antibiotics out of the cell. (4) Secondary Active Transporters use the electrochemical gradient created by primary active transport systems like the sodium pump. (5) Endocytosis (phagocytosis and pinocytosis), a process by which substances are incorporated into the cell. This is mediated by vesicles, which contain the material to be endocytosed surrounded by plasma membrane. Endocytosis can be clathrin- and caveolin-mediated. The substance to be internalized is first bound by a receptor in the surface of the plasma membrane. Invagination of the membrane forms a clathrin- or caveolin-coated vesicle that is internalized into the cell. (6) Exocytosis, the process by which cells moves substance to the medium. This requires that the molecules to be exported be enclosed in vesicles formed in the trans Golgi and then trafficked to the plasma membrane, with which they fuse and release their content outside the cell. Keywords lipid bilayer simple diffusion facilitated diffusion carrier channel aquaporin active transport Secondary Active Transport endocytosis exocytosis The surface of cells is covered by the plasma membrane, a very thin film (6–10 nm thick) consisting of lipids, proteins, and carbohydrates. Far from being just a shell, the plasma membrane is a structure with remarkable functional properties: (1) it is a selectively permeable barrier, which controls the passage of solutes and water and prevents the random mixture of components of the extracellular environment with those of the intracellular space or cytosol. Transport systems at the plasma membrane are largely responsible for maintaining the constancy of the cell cytosol

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  Cell Boundaries

  How Membranes and Their Proteins Work

  • Stephen White, Gunnar von Heijne, Donald Engelman, Stephen H White, Donald M Engelman(Authors)
  • 2021(Publication Date)
  • Garland Science

    (Publisher)

  Chapter 13 .

  How are ion and solute pumping coupled to ATP consumption in primary transporters? We first examine the family of P-type ATPases, and in particular the Na+ /K+ -ATPase, responsible for establishing the transmembrane electrochemical gradient of axons and other cells, and the Ca2+ -ATPase that maintains strong Ca2+ gradients across the muscle sarcoplasmic reticulum as an essential feature of the control of muscle contraction. We then consider another very large family of proteins, the so-called ATP binding cassette (ABC) transporters, which use ATP for pumping all sorts of molecules across cell membranes. Finally, we consider an interesting family of ATP-driven transporters, the energy-coupling factor (ECF) transporters, in which the substrate-binding subunit appears to “topple” in the membrane in response to ATP hydrolysis.

  12.1 P-Type ATPases

  P-type ATPases are found throughout the living world. P-type ATPases actively transport a variety of ions—and even lipids—across membranes. The name is meant to reflect a key mechanistic feature, namely, that a conserved Asp residue is phosphorylated during the reaction cycle. All P-type ATPases have five domains that cooperate during the reaction cycle: the cytoplasmic actuator (A), nucleotide-binding (N), and phosphorylation (P) domains, and the two membrane-embedded transport (T) and class-specific support (S) domains (Figure 12.2 ). In many cases, there is also a sixth regulatory (R) domain attached to the N- or C-terminus (or both) of the protein. We will focus the discussion on two P-type ATPases: the historically important Na+ /K+ -ATPase and the currently best understood P-type ATPase, the Ca2+

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