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Osmosis, Diffusion, and Membrane Transport Bio 219 Napa Valley College Dr
Osmosis, Diffusion, and Membrane Transport Bio 219 Napa Valley College Dr. Adam Ross Overview In order to understand how cells regulate themselves, we must first understand how things move into and out of cells Diffusion • Diffusion is the movement of particles from an area of high charge or concentration to an area of lower charge or concentration • Referred to as moving “down” a charge or concentration gradient • Ex. H+ ions in mitochondria moving through ATP synthase • Result of random molecular motion • Fick’s Law of Diffusion gives rate of diffusion: • Rate = P A (Cout – Cin) / (x) • Rate is proportional to permeability (P), surface area (A), concentration gradient (Cout – Cin); inversely proportional to diffusion distance or membrane thickness (x) Gradients • Concentration • Caused by unequal distribution of a substance on either side of the membrane • If the inside of a cell is negative, it will attract positively charged things • Electrical (charge) • Caused by unequal distribution of charge on either side of the membrane Diffusion Osmosis • Osmosis is the movement of solvent through a semi permeable membrane in order to balance the solute concentration on either side of the membrane. • In cells the solvent is water • Water can cross membranes Osmosis Osmolarity • Total concentration of all solutes in a solution • 1 Osm = 1 mole solute/ L • Have to account for both atoms in salts • 1M NaCl +1 L H2O → 1M Na+ + 1M Cl ≈ 2 Osm • Plasma = 290 mOsm Osmotic pressure • This is the actual driving force for net water movement • Depends on -
Membrane Transport, Absorption and Distribution of Drugs
Chapter 2 1 Pharmacokinetics: Membrane Transport, Absorption and Distribution of Drugs Pharmacokinetics is the quantitative study of drug movement in, through and out of the body. The overall scheme of pharmacokinetic processes is depicted in Fig. 2.1. The intensity of response is related to concentration of the drug at the site of action, which in turn is dependent on its pharmacokinetic properties. Pharmacokinetic considerations, therefore, determine the route(s) of administration, dose, and latency of onset, time of peak action, duration of action and frequency of administration of a drug. Fig. 2.1: Schematic depiction of pharmacokinetic processes All pharmacokinetic processes involve transport of the drug across biological membranes. Biological membrane This is a bilayer (about 100 Å thick) of phospholipid and cholesterol molecules, the polar groups (glyceryl phosphate attached to ethanolamine/choline or hydroxyl group of cholesterol) of these are oriented at the two surfaces and the nonpolar hydrocarbon chains are embedded in the matrix to form a continuous sheet. This imparts high electrical resistance and relative impermeability to the membrane. Extrinsic and intrinsic protein molecules are adsorbed on the lipid bilayer (Fig. 2.2). Glyco- proteins or glycolipids are formed on the surface by attachment to polymeric sugars, 2 aminosugars or sialic acids. The specific lipid and protein composition of different membranes differs according to the cell or the organelle type. The proteins are able to freely float through the membrane: associate and organize or vice versa. Some of the intrinsic ones, which extend through the full thickness of the membrane, surround fine aqueous pores. CHAPTER2 Fig. -
Cellular Transport Notes About Cell Membranes
Cellular Transport Notes @ 2011 Center for Pre-College Programs, New Jersey Institute of Technology, Newark, New Jersey About Cell Membranes • All cells have a cell membrane • Functions: – Controls what enters and exits the cell to maintain an internal balance called homeostasis TEM picture of a – Provides protection and real cell membrane. support for the cell @ 2011 Center for Pre-College Programs, New Jersey Institute of Technology, Newark, New Jersey 1 About Cell Membranes (continued) 1.Structure of cell membrane Lipid Bilayer -2 layers of phospholipids • Phosphate head is polar (water loving) Phospholipid • Fatty acid tails non-polar (water fearing) • Proteins embedded in membrane Lipid Bilayer @ 2011 Center for Pre-College Programs, New Jersey Institute of Technology, Newark, New Jersey Polar heads Fluid Mosaic love water Model of the & dissolve. cell membrane Non-polar tails hide from water. Carbohydrate cell markers Proteins @ 2011 Center for Pre-College Programs, New Jersey Institute of Technology, Newark, New Jersey 2 About Cell Membranes (continued) • 4. Cell membranes have pores (holes) in it • Selectively permeable: Allows some molecules in and keeps other molecules out • The structure helps it be selective! Pores @ 2011 Center for Pre-College Programs, New Jersey Institute of Technology, Newark, New Jersey Structure of the Cell Membrane Outside of cell Carbohydrate Proteins chains Lipid Bilayer Transport Protein Phospholipids Inside of cell (cytoplasm) @ 2011 Center for Pre-College Programs, New Jersey Institute of Technology, Newark, New Jersey 3 Types of Cellular Transport • Passive Transport celldoesn’tuseenergy 1. Diffusion 2. Facilitated Diffusion 3. Osmosis • Active Transport cell does use energy 1. -
CO2 Permeability of Biological Membranes and Role of CO2 Channels
membranes Review CO2 Permeability of Biological Membranes and Role of CO2 Channels Volker Endeward, Mariela Arias-Hidalgo, Samer Al-Samir and Gerolf Gros * Molekular-und Zellphysiologie, AG Vegetative Physiologie–4220–Medizinische Hochschule Hannover, 30625 Hannover, Germany; [email protected] (V.E.); [email protected] (M.A.-H.); [email protected] (S.A.-S.) * Correspondence: [email protected]; Fax: +49-511-5322938 Received: 17 September 2017; Accepted: 18 October 2017; Published: 24 October 2017 Abstract: We summarize here, mainly for mammalian systems, the present knowledge of (a) the membrane CO2 permeabilities in various tissues; (b) the physiological significance of the value of the CO2 permeability; (c) the mechanisms by which membrane CO2 permeability is modulated; (d) the role of the intracellular diffusivity of CO2 for the quantitative significance of cell membrane CO2 permeability; (e) the available evidence for the existence of CO2 channels in mammalian and artificial systems, with a brief view on CO2 channels in fishes and plants; and, (f) the possible significance of CO2 channels in mammalian systems. Keywords: CO2 permeability; membrane cholesterol; protein CO2 channels; aquaporins; Rhesus proteins; aquaporin-1-deficient mice 1. Introduction This review intends to update the state of this field as it has been given by Endeward et al. [1] in 2014. In addition, we attempt to give a compilation of all of the lines of evidence that have so far been published demonstrating the existence of protein CO2 channels and their contributions to membrane CO2 permeability. We also give a compilation of the recently described remarkable variability of the CO2 permeability in mammalian cell membranes. -
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. -
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. -
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. -
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. -
Cell Transport
Cells and their Environment Transport occurs across the cell membrane and helps a cell to maintain homeostasis. Cell part responsible: 5/16/14 1 1. Movement of materials across the membrane is called transport. A. Passive Transport - WITHOUT the use of energy • Driven by Kinetic energy/Brownian motion B. Active Transport - WITH the use of energy- against a concentration gradient 5/16/14 2 2. Concentration Gradient- difference in concentration from one area to another Visual Concept 5/16/14 3 3. Diffusion is passive/no energy. a) Diffusion- high to low concentration. b) Quicker at higher temps c) Occurs until an equilibrium is reached 5/16/14 4 4. Osmosis is the diffusion of water molecules directly through the cell's membrane. 5/16/14 5 5. If a cell is in a solution that is….. a) Hypertonic it shrinks (higher concentration of dissolved particles outside than inside of the cell) b) Hypotonic it expands (lower concentration of dissolved particles outside compared with inside of the cell) c) Isotonic no change (same concentration of dissolved particles outside as inside of the cell. 5/16/14 6 Graphic Organizer Hypertonic Hypotonic Isotonic DRAWINGS: For each category, draw a cell in solution. For each picture, show solute particles in your solution and also in your cell. Label solvent line and solute particles. Show if water is entering or leaving the cell using arrows. WRITE ABOUT IT: For each category, answer the following in complete sentences. 1) Is water moving into or out of the cell, or neither? 2) Is the cell shrinking, expanding or staying the same? 3) Are there more solute particles inside 5/16/14the cell or in solution, or neither? 7 Question: What would happen to an animal cell placed into a HYPERtonic solution? 5/16/14 8 (It would shrink- plasmolysis) 6. -
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. -
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. -
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.