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Mechanism of Na+-K+ Atpase Is As Follows Input Template for Content Writers (e-Text and Learn More) 1. Details of Module and its Structure Module Detail Subject Name Botany Paper Name Cell Biology Module Name/Title Cell membrane and Cellular transport III Module Id <Module Id> Pre-requisites Objectives To understand principle and mechanism of primary active transport Keywords Active transport, Electochemical gradient Primary active transport, Facilitated Diffusion, Carrier proteins for primary active Structure of Module / Syllabus of a module (Define Topic / Sub-topic of module ) Passive transport <Definition>, <Types>, <Mechanism> Passive transport < Introduction > < Active transport>, < Electochemical gradient> < primary active transport> < Facilitated Diffusion > < carrier proteins for primary active transport > Management of Library and Information Network Library Science Network 2. 2. Development Team Role Name Affiliation National Coordinator <National Coordinator Name> Subject Coordinator Dr Sujata Bhargava Paper Coordinator Dr Nutan Malpathak Content Writer/Author (CW) Dr Pradnya Kedari Content Reviewer (CR) <CR Name> Language Editor (LE) <LE Name> Management of Library and Information Network Library Science Network TABLE OF CONTENTS (for textual content) 1 Introduction 2 Active transport 3 Electrochemical gradient 4 Primary active transport 5 Carrier Proteins or pumps for Active Transport Management of Library and Information Network Library Science Network Cell membrane and cellular transport III 1. Introduction Active transport is a transport of molecules against its concentration gradient. Molecules are carried from region of lower concentration to region of higher concentration. This process face resistance and so it has to utilise energy to overcome this resistance and carryout this transport. Therefore it is called as active transport. The process is also known as uphill transport. This energy is usually in the form of adenosine triphosphate (ATP). This ATP is utilized directly/ indirectly. Cell need to move molecule - against concentration gradient too. Active transport is a transport of a molecule which requires expenditure of energy to move solute against conc. gradient, using energy. Active transport mechanisms use cell’s energy, usually in the form of Adenosine triphosphate (ATP). In case of primary active transport ATP is utilized directly. It is an uphill transport. Let’s revise the difference between passive transport and active transport? Active and passive transport are terms that are utilized in terms of plant, animals as well as human body. 2 Active transport Active transport involves carrying a molecule against the concentration gradient, and it utilizes energy, whereas passive transport occurs according to concentration gradient and therefore it does not require any energy. During active transport, as resistance is more it is called as uphill process, whereas passive transport face no resistance and therefore is referred as downhill process. Some active transport mechanisms move small-molecular weight materials, such as ions, through the membrane. Other mechanisms transport much larger molecules. An example of active transport is - uptake of salt by cells through a sodium pump 3 Electrochemical Gradient? living systems, concentration gradients are more complex. In a cell, ions are constantly moving in and out of cells. They posses either positive or negative cgarge. Cell also contains proteins which do not move across the membrane. These proteins are Management of Library and Information Network Library Science Network mostly negatively charged. This creates an electrical gradient i.e difference of charge, across the plasma membrane. Interior of a living cell is electrically negative W. R. t. extracellular fluid. At the same time, cells possess higher concentrations of potassium (K+) and lower concentrations of sodium (Na+) than the extracellular fluid. Therefore in a living cell, the concentration gradient of Na+ tends to drive it into the cell, and the electrical gradient of Na+ (a positive ion) also tends to drive it inward to the negatively charged interior. This makes the situation more complex for other elements such as potassium. As a living cell is electrically negative, electrical gradient of K+, a positive ion, also tends to drive it into the cell, but concentration of K+ ions is greater into the cell as compare to extracellular fluids. Therefore the concentration gradient of K+ tends to drive K+ out of the cell. Such combined gradient of concentration and electrical charge affects an ion and is called its electrochemical gradient. If it’s a Fact that Potassium solution Injection is lethal. My question is - Why do you think a potassium solution injection is lethal? Answer to this question is that + + • Cell- have high K conc. In the cytoplasm, and it has high conc. of Na outside, + • Due to K Injection,thete is high conce of K+ ions outside the cell which cahnges electrochemical gradient. • Sodium/potassium potential from heart muscle, play important role in transmitting muscle contraction signal. • Due to change in this electrochemical gradient, heart fails to send the beating signal, and therefore person dies. • That is the reason why a potassium solution injection is lethal, but during heart surgeries, This K+ injections are used during in appropriate amount to stop the heart from beating during surgery. Moving Against a Gradient For a cell, it needs to spend an energy to move a substances against a concentration or electrochemical gradient. This energy is gained from hydrolysis of ATP which is generated through the cell’s metabolism. Small substances are constantly passing through plasma membranes. It keeps on fluctuating the electrochemical gradient of a cell. There is special active transport mechanism followed by a cell to carry outs active transport process, which is known as pumps. Pumps work against this electrochemical gradient. Active transport maintains concentrations of ions and other substances needed by living cells in response to these passive movements. Cell needs to spend much of its supply of metabolic energy to maintain these processes. (Most of a red blood cell’s metabolic energy is used to maintain the imbalance between exterior and interior sodium and potassium levels required by the cell.) Management of Library and Information Network Library Science Network Because active transport mechanisms depend on a cell’s metabolism for energy, they are sensitive to many metabolic poisons that interfere with the supply of ATP. Primary active transport There exist two mechanisms for the transport of small-molecular weight material and small molecules. 1. Primary active transport which moves ions across a membrane and creates a difference in charge across that membrane. This is directly dependent on ATP. 2. Secondary active transport which describes the movement of material that is due to the electrochemical gradient established by primary active transport that does not directly require ATP. The cell makes use of membrane pumps to accomplish active transport. Pumps can convert free energy into different forms, depending on which form is required by the cell at a given time. This property makes membrane pumps a convenient choice for mediating active transport as they can provide the energy needed to initiate the transport. The two main types of pumps employed by the cell are P-type ATPases and ATP-binding cassette transporters (eg-ABCs). Both of these pumps are powered by ATP. One method by which these pumps can perform active transport is by binding to ATP. This binding, followed by hydrolysis which induces a conformational change in the pump that allows bound ions to be transported across the cell membrane. These pumps can also use active transport to establish favorable concentration gradients for separate transport processes. For example, one pump can create a given concentration gradient by performing active transport on a certain ion, and then another pump can make use of this new concentration gradient and facilitat ion diffusion down the concentration gradient. Thus the cell can couple active transport with passive transport in order to efficiently use the results of one process to drive another process to completion. 4 Carrier Proteins for Active Transport Membrane show certain mechanisms to adapt the process of transport against the concentration gradient. An important membrane adaption for active transport is the presence of specific carrier proteins or pumps. They facilitate this movement. Management of Library and Information Network Library Science Network There are three types of these proteins or transporters present on a membrane. Uniporter which carries one specific ion or molecule at a time. Symporter which carries two different ions or molecules at a time. Both the molecules move in the same direction. And Antiporter, which also carries two different ions or molecules ata time, but in different directions. All of these transporters can also transport small, uncharged organic molecules like glucose. These three types of carrier proteins are also found in facilitated diffusion, but they do not require ATP to work in that process. Some examples of pumps for active transport are Na+–K+ ATPase, which carries sodium and potassium ions, and H+–K+ ATPase, which carries hydrogen and potassium ions. Both of these are antiporter carrier proteins. Two other carrier proteins are Ca2+ ATPase and H+ ATPase, which carry only calcium and only hydrogen ions, respectively. Both are pumps. Sodium-potassium
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