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Why Is Atp Required For Membrane Pump Systems To Operate

Active Transport - An Overview | Sciencedirect Topics

Active Transport - An Overview | Sciencedirect Topics

Active transport is defined as movement of a solute from a region of low electrochemical potential on one side of the cell membrane to a region of higher electrochemical potential on the opposite side. Joseph Feher, in Quantitative Human Physiology (Second Edition) , 2017 This chapter describes active transport in terms of the energetics of transport, using the electrochemical potential of the transported material on both sides of the membrane, and the free energy of ATP hydrolysis. The free energy change for sodium, potassium, or calcium entry is calculated for resting cardiomyocytes that have a resting membrane potential. These free energy changes are then used to calculate the overall free energy for the sodiumcalcium exchanger or for the sodiumpotassium pump. These calculations illustrate thermodynamic coupling between energy-yielding processes and energy-consuming processes. The mechanism of the Na,K-ATPase is considered. Examples of primary and secondary active transport are given. Joseph Feher, in Quantitative Human Physiology , 2012 This chapter describes active transport in terms of the energetics of transport, using the electrochemical potential of the transported material on both sides of the membrane, and the free energy of ATP hydrolysis. The free energy change for sodium, potassium, or calcium entry is calculated for resting cardiomyocytes that have a resting membrane potential. These free energy changes are then used to calculate the overall free energy for the sodiumcalcium exchanger or for the sodiumpotassium pump. These calculations illustrate thermodynamic coupling between energy-yielding processes and energy-consuming processes. The mechanism of the Na,K-ATPase is considered. Examples of primary and secondary active transport are given. Primary acti Continue reading >>

Nervous System - Active Transport: The Sodium-potassium Pump | Britannica.com

Nervous System - Active Transport: The Sodium-potassium Pump | Britannica.com

Active transport: the sodium-potassium pump Since the plasma membrane of the neuron is highly permeable to K+ and slightly permeable to Na+, and since neither of these ions is in a state of equilibrium (Na+ being at higher concentration outside the cell than inside and K+ at higher concentration inside the cell), then a natural occurrence should be the diffusion of both ions down their electrochemical gradientsK+ out of the cell and Na+ into the cell. However, the concentrations of these ions are maintained at constant disequilibrium, indicating that there is a compensatory mechanism moving Na+ outward against its concentration gradient and K+ inward. This mechanism is the sodium-potassium pump. Actually a large protein molecule that traverses the plasma membrane of the neuron, the pump presents receptor areas to both the cytoplasm and the extracellular environment . That part of the molecule facing the cytoplasm has a high affinity for Na+ and a low affinity for K+, while that part facing the outside has a high affinity for K+ and a low affinity for Na+. Stimulated by the action of the ions on its receptors, the pump transports them in opposite directions against their concentration gradients. If equal amounts of Na+ and K+ were transported across the membrane by the pump, the net charge transfer would be zero; there would be no net flow of current and no effect on the membrane potential. In fact, in many neurons three sodium ions are transported for every potassium ion; sometimes the ratio is three sodium ions for every two potassium ions, and in a few neurons it is two sodium ions for one potassium ion. This inequality of ionic transfer produces a net efflux of positive charge, maintaining a polarized membrane with the inner surface slightly negative in relation to Continue reading >>

Bio Cells & Processes

Bio Cells & Processes

fx: locomotion, 1 or more attached to cell wall/distributed over cell structure- shorter, thinner, and straighter function- attachment compared to flagella used for locomotion glycolax: protects bacteria from immune attack (external danger) composed of polysaccharides & polypeptides bacteria's main method of reproduction- cells replicate genetic material and divide into daughter cells conjugation does not involve the fusion of gametes or zygotes examples of active transport & they use ATP. channels are less specific than carriers: carriers only allow specific things through, channels allow lots of things so long as they have the right size/cahrge required to build & maintain cell membranes, regulates membrane permeability and fluidity PROBLEM ONE (cell is 2 M placed in a solution w a concentration of 2.5 M): it is possible that the cell is already in equilibrium w its surroundings PROBLEM ONE (cell is 2 M placed in a solution w a concentration of 2.5 M): initially, solute concentration is greater outside the cell than inside PROBLEM ONE (cell is 2 M placed in a solution w a concentration of 2.5 M): water will enter the cell because solute potential is lower inside the cell than outside PROBLEM ONE (cell is 2 M placed in a solution w a concentration of 2.5 M): the cell will become flaccid because the pressure potential is greater outside the cell than inside PROBLEM ONE (cell is 2 M placed in a solution w a concentration of 2.5 M): the cell is already in equilibrium w its surrounding because of the combination of pressure potential and solute potential inside and outside the cell PROBLEM ONE (cell is 2 M placed in a solution w a concentration of 2.5 M): initially the cytoplasm is hypertonic to the surrounding solution PROBLEM ONE (cell is 2 M placed in a solution w a co Continue reading >>

Active Transport - An Overview | Sciencedirect Topics

Active Transport - An Overview | Sciencedirect Topics

Active transport is defined as movement of a solute from a region of low electrochemical potential on one side of the cell membrane to a region of higher electrochemical potential on the opposite side. Joseph Feher, in Quantitative Human Physiology (Second Edition) , 2017 This chapter describes active transport in terms of the energetics of transport, using the electrochemical potential of the transported material on both sides of the membrane, and the free energy of ATP hydrolysis. The free energy change for sodium, potassium, or calcium entry is calculated for resting cardiomyocytes that have a resting membrane potential. These free energy changes are then used to calculate the overall free energy for the sodiumcalcium exchanger or for the sodiumpotassium pump. These calculations illustrate thermodynamic coupling between energy-yielding processes and energy-consuming processes. The mechanism of the Na,K-ATPase is considered. Examples of primary and secondary active transport are given. Joseph Feher, in Quantitative Human Physiology , 2012 This chapter describes active transport in terms of the energetics of transport, using the electrochemical potential of the transported material on both sides of the membrane, and the free energy of ATP hydrolysis. The free energy change for sodium, potassium, or calcium entry is calculated for resting cardiomyocytes that have a resting membrane potential. These free energy changes are then used to calculate the overall free energy for the sodiumcalcium exchanger or for the sodiumpotassium pump. These calculations illustrate thermodynamic coupling between energy-yielding processes and energy-consuming processes. The mechanism of the Na,K-ATPase is considered. Examples of primary and secondary active transport are given. Yaar Demirel Continue reading >>

Molecular Biology Of The Cell. 4th Edition.

Molecular Biology Of The Cell. 4th Edition.

The process by which a carrier protein transfers a solute molecule across the lipid bilayer resembles an enzyme-substrate reaction, and in many ways carriers behave like enzymes. In contrast to ordinary enzyme-substrate reactions, however, the transported solute is not covalently modified by the carrier protein, but instead is delivered unchanged to the other side of the membrane. Each type of carrier protein has one or more specific binding sites for its solute (substrate). It transfers the solute across the lipid bilayer by undergoing reversible conformational changes that alternately expose the solute-binding site first on one side of the membrane and then on the other. A schematic model of how such a carrier protein is thought to operate is shown in Figure 11-6. When the carrier is saturated (that is, when all solute-binding sites are occupied), the rate of transport is maximal. This rate, referred to as Vmax, is characteristic of the specific carrier and reflects the rate with which the carrier can flip between its two conformational states. In addition, each transporter protein has a characteristic binding constant for its solute, Km, equal to the concentration of solute when the transport rate is half its maximum value (Figure 11-7). As with enzymes, the binding of solute can be blocked specifically by either competitive inhibitors (which compete for the same binding site and may or may not be transported by the carrier) or noncompetitive inhibitors (which bind elsewhere and specifically alter the structure of the carrier). As we discuss below, it requires only a relatively minor modification of the model shown in Figure 11-6 to link the carrier protein to a source of energy in order to pump a solute uphill against its electrochemical gradient. Cells carry out su Continue reading >>

Membrane Transport - Wikipedia

Membrane Transport - Wikipedia

In cellular biology , membrane transport refers to the collection of mechanisms that regulate the passage of solutes such as ions and small molecules through biological membranes , which are lipid bilayers that contain proteins embedded in them. The regulation of passage through the membrane is due to selective membrane permeability - a characteristic of biological membranes which allows them to separate substances of distinct chemical nature. In other words, they can be permeable to certain substances but not to others. [1] The movements of most solutes through the membrane are mediated by membrane transport proteins which are specialized to varying degrees in the transport of specific molecules. As the diversity and physiology of the distinct cells is highly related to their capacities to attract different external elements, it is postulated that there is a group of specific transport proteins for each cell type and for every specific physiological stage[1]. This differential expression is regulated through the differential transcription of the genes coding for these proteins and its translation, for instance, through genetic-molecular mechanisms, but also at the cell biology level: the production of these proteins can be activated by cellular signaling pathways , at the biochemical level, or even by being situated in cytoplasmic vesicles. [2] While studies on membrane permeability and osmosis dates back to the 18th century, works on membrane transporters or carriers begun in the 1930s. [3] Thermodynamically the flow of substances from one compartment to another can occur in the direction of a concentration or electrochemical gradient or against it. If the exchange of substances occurs in the direction of the gradient, that is, in the direction of decreasing potentia Continue reading >>

Transport Across Cell Membranes

Transport Across Cell Membranes

Facilitated Diffusion of Ions Ligand-gated ion channels. External Ligands Internal Ligands Mechanically-gated ion channels Voltage-gated ion channels The Patch Clamp Technique Facilitated Diffusion of Molecules Active Transport Direct Active Transport The Na+/K+ ATPase The H+/K+ ATPase The Ca2+ ATPase of skeletal muscle ABC Transporters Indirect Active Transport Symport Pumps Antiport Pumps Some inherited ion-channel diseases Osmosis Hypotonic Solutions Isotonic Solutions Hypertonic Solutions All cells acquire the molecules and ions they need from their surrounding extracellular fluid (ECF). There is an unceasing traffic of molecules and ions in and out of the cell through its plasma membrane Examples: glucose, Na+, Ca2+ In eukaryotic cells, there is also transport in and out of membrane-bounded intracellular compartments such as the nucleus, endoplasmic reticulum, and mitochondria. Examples: proteins, mRNA, Ca2+, ATP 1. Relative concentrations Molecules and ions move spontaneously down their concentration gradient (i.e., from a region of higher to a region of lower concentration) by diffusion. Molecules and ions can be moved against their concentration gradient, but this process, called active transport, requires the expenditure of energy (usually from ATP). 2. Lipid bilayers are impermeable to most essential molecules and ions. The lipid bilayer is permeable to water molecules and a few other small, uncharged, molecules like oxygen (O) and carbon dioxide (CO). These diffuse freely in and out of the cell. The diffusion of water through the plasma membrane is of such importance to the cell that it is given a special name: osmosis. Lipid bilayers are not permeable to: ions such as K+, Na+, Ca2+ (called cations because when subjected to an electric field they migrate towa Continue reading >>

16 3.1 The Cell Membrane

16 3.1 The Cell Membrane

Structure and Composition of the Cell Membrane The cell membrane is an extremely pliable structure composed primarily of back-to-back phospholipids (a “bilayer”). Cholesterol is also present, which contributes to the fluidity of the membrane, and there are various proteins embedded within the membrane that have a variety of functions. A single phospholipid molecule has a phosphate group on one end, called the “head,” and two side-by-side chains of fatty acids that make up the lipid tails (Figure 1). The phosphate group is negatively charged, making the head polar and hydrophilic—or “water loving.” A hydrophilic molecule (or region of a molecule) is one that is attracted to water. The phosphate heads are thus attracted to the water molecules of both the extracellular and intracellular environments. The lipid tails, on the other hand, are uncharged, or nonpolar, and are hydrophobic—or “water fearing.” A hydrophobic molecule (or region of a molecule) repels and is repelled by water. Some lipid tails consist of saturated fatty acids and some contain unsaturated fatty acids. This combination adds to the fluidity of the tails that are constantly in motion. Phospholipids are thus amphipathic molecules. An amphipathic molecule is one that contains both a hydrophilic and a hydrophobic region. In fact, soap works to remove oil and grease stains because it has amphipathic properties. The hydrophilic portion can dissolve in water while the hydrophobic portion can trap grease in micelles that then can be washed away. The cell membrane consists of two adjacent layers of phospholipids. The lipid tails of one layer face the lipid tails of the other layer, meeting at the interface of the two layers. The phospholipid heads face outward, one layer exposed to the interi Continue reading >>

Active Transport

Active Transport

Electrochemical Gradient To move substances against the membrane’s electrochemical gradient, the cell utilizes active transport, which requires energy from ATP. Learning Objectives Define an electrochemical gradient and describe how a cell moves substances against this gradient Key Takeaways The electrical and concentration gradients of a membrane tend to drive sodium into and potassium out of the cell, and active transport works against these gradients. To move substances against a concentration or electrochemical gradient, the cell must utilize energy in the form of ATP during active transport. Primary active transport, which is directly dependent on ATP, moves ions across a membrane and creates a difference in charge across that membrane. Secondary active transport, created by primary active transport, is the transport of a solute in the direction of its electrochemical gradient and does not directly require ATP. Carrier proteins such as uniporters, symporters, and antiporters perform primary active transport and facilitate the movement of solutes across the cell’s membrane. Key Terms adenosine triphosphate: a multifunctional nucleoside triphosphate used in cells as a coenzyme, often called the “molecular unit of energy currency” in intracellular energy transfer active transport: movement of a substance across a cell membrane against its concentration gradient (from low to high concentration) facilitated by ATP conversion electrochemical gradient: The difference in charge and chemical concentration across a membrane. Electrochemical Gradients Simple concentration gradients are differential concentrations of a substance across a space or a membrane, but in living systems, gradients are more complex. Because ions move into and out of cells and because cells con Continue reading >>

Active Transport

Active Transport

Concentration Gradients The concentration of most molecules inside a cell is different than the concentration of molecules in the surrounding environment. The plasma membrane separates the internal environment of the cell from the fluid bathing the cell and regulates the flow of molecules both into and out of the cell. The second law of thermodynamics states that molecules, whether in the gas or liquid state, will move spontaneously from an area of higher concentration to an area of lower concentration or down their concentration gradient. A concentration gradient can be likened to water stored behind a dam. The water behind the dam will flow through the dam via any available channel to the other side. The energy from the water moving through the dam can be harnessed to make electricity. Water can also be pumped in the opposite direction from the river below the dam up to the reservoir behind the dam, with an expenditure of energy. Cellular membranes act somewhat like a dam. They block the movement of many types of molecules and have specific channels, transporters and pumps to provide pathways for the movement of certain molecules across the membrane. When a molecule moves down its concentration gradient using one of these membrane channels or transporters, the process is called facilitated diffusion. In facilitated diffusion, no input of energy is needed to move the molecules. Instead, the potential energy of the concentration gradient powers the movement, just like water flowing out of a dam. For further diffusion, the channel or transporter does not determine in which direction the molecules will move, it only provides a pathway for the movement. In cells, some molecules must be moved against their concentration gradient to increase their concentration inside or out Continue reading >>

Active Transport By Atp-powered Pumps - Molecular Cell Biology - Ncbi Bookshelf

Active Transport By Atp-powered Pumps - Molecular Cell Biology - Ncbi Bookshelf

Model of the mechanism of action of muscleCa2+ ATPase, which is located in thesarcoplasmic reticulum (SR) membrane. Only one of the two subunits of this P-class pump isdepicted. E1 and E2 are alternate conformational forms of theprotein (more...) Thus phosphorylation of the muscle calcium pump by ATP favors conversion of E1 toE2, and dephosphorylation favors the conversion of E2 to E1. While onlyE2 P, not E1~P, is actually hydrolyzed, thefree energy of hydrolysis of the aspartyl-phosphate bond in E1~P is greater thanthat for E2 P. The reduction in free energy ofthe aspartyl-phosphate bond in E2 P, relativeto E1~P, can be said to power the E1 E2conformational change. The affinity of Ca2+ for thecytosolic-facing binding sites in E1 is a thousandfold greater than the affinityof Ca2+ for the exoplasmic-facing sites in E2; thisdifference enables the protein to transport Ca2+unidirectionally from the cytosol , where it binds tightly to the pump, to theexoplasm, where it is released. Much evidence supports the model depicted in Figure 15-11 . For instance, the muscle calcium pump has beenisolated with phosphate linked to an aspartate residue, and spectroscopicstudies have detected slight alterations in protein conformation during theE1 E2 conversion. On the basis of theproteins amino acid sequence and various biochemical studies,investigators proposed the structural model for the catalytic subunit shown in Figure 15-12 . The membrane -spanning helices are thought to form the passageway throughwhich Ca2+ ions move. The bulk of the subunit consists ofcytosolic globular domains that are involved in ATP binding, phosphorylation ofaspartate, and energy transduction. These domains are connected bystalks to the membrane-embedded domain . Schematic structural model for the catalytic Continue reading >>

Biology4kids.com: Cell Function: Active Transport

Biology4kids.com: Cell Function: Active Transport

Active transport describes what happens when a cell uses energy to transport something. We're not talking about phagocytosis (cell eating) or pinocytosis (cell drinking) in this section. We're talking about the movement of individual molecules across the cell membrane . The liquids inside and outside of cells have different substances. Sometimes a cell has to work and use some energy to maintain a proper balance of ions and molecules. Active transport usually happens across the cell membrane. There are thousands of proteins embedded in the cell's lipid bilayer. Those proteins do much of the work in active transport. They are positioned to cross the membrane so one part is on the inside of the cell and one part is on the outside. Only when they cross the bilayer are they able to move molecules and ions in and out of the cell. The membrane proteins are very specific. One protein that moves glucose will not move calcium (Ca) ions. There are hundreds of types of these membrane proteins in the many cells of your body. Many times, proteins have to work against a concentration gradient. That term means they are pumping something (usually ions) from areas of lower to higher concentration. This happens a lot in neurons . The membrane proteins are constantly pumping ions in and out to get the membrane of the neuron ready to transmit electrical impulses. Even though these proteins are working to keep the cell alive, their activity can be stopped. There are poisons that stop the membrane proteins from transporting their molecules. Those poisons are called inhibitors. Sometimes the proteins are destroyed and other times they are just plugged up. Imagine that you are a cell and have ten proteins working to pump calcium into the cell. What if a poison came along and blocked eight of Continue reading >>

Biology Flashcards | Quizlet

Biology Flashcards | Quizlet

Involved in the manufacture of substances, detoxifying harmful products and the storage and release of substances. Both are involved in transporting different materials within cells, but are not passive channels like pipes List one similarity between rough ER and smooth ER The rough ER transports proteins and has a network of channels while the smooth ER uses its outer membrane surface as a site of synthesis and detoxifies harmful products. Identify 2 differences between the rough ER and the smooth ER, one structural and one functional a slender thread-like structure, especially a microscopic whip-like appendage which enables many protozoa, bacteria, spermatozoa, etc. to swim. Minute hairlike organelles, identical in structure to flagella, that line the surfaces of certain cells and beat in rhythmic waves, providing locomotion to ciliate protozoans and moving liquids along internal epithelial tissue in animals a microscopic network of protein filaments and tubules in the cytoplasm of many living cells, giving them shape and coherence. a minute particle consisting of RNA and associated proteins found in large numbers in the cytoplasm of living cells. They bind messenger RNA and transfer RNA to synthesize polypeptides and proteins. -Solubility in lipids - lipophilic molecules cross easily -Charge - positive or negative charge molecules have difficulty crossing - uncharged cross easily -Concentration gradient - substances more likely to cross with concentration gradient Factors affecting transport across the plasma membrane Bacteria in deep sea vents use chemicals to produce own energy Glucose + Oxygen -> Carbon dioxide + water + energy (ATP) Water + Carbon dioxide -> glucose + oxygen Smaller diameters have a higher SA:V ratio What are the two major components of a plasma Continue reading >>

Help Us Do More

Help Us Do More

Passive transport is a great strategy for moving molecules into or out of a cell. It's cheap, it's easy, and all the cell has to do is sit there and let the molecules diffuse in. But...it also doesn't work in every situation. For instance, suppose the sugar glucose is more concentrated inside of a cell than outside. If the cell needs more sugar in to meet its metabolic needs, how can it get that sugar in? Here, the cell can't import glucose for free using diffusion, because the natural tendency of the glucose will be to diffuse out rather than flowing in. Instead, the cell must bring in more glucose molecules via active transport. In active transport, unlike passive transport, the cell expends energy (for example, in the form of ATP) to move a substance against its concentration gradient. Here, we’ll look in more detail at gradients of molecules that exist across cell membranes, how they can help or hinder transport, and how active transport mechanisms allow molecules to move against their gradients. We have already discussed simple concentration gradients, in which a substance is found in different concentrations over a region of space or on opposite sides of a membrane. However, because atoms and molecules can form ions and carry positive or negative electrical charges, there may also be an electrical gradient, or difference in charge, across a plasma membrane. In fact, living cells typically have what’s called a membrane potential, an electrical potential difference (voltage) across their cell membrane. Image depicting the charge and ion distribution across the membrane of a typical cell. Overall, there are more positive charges on the outside of the membrane than on the inside. The concentration of sodium ions is lower inside the cell than in the extracellular f Continue reading >>

Overview Of Membrane Transport Proteins - Molecular Cell Biology - Ncbi Bookshelf

Overview Of Membrane Transport Proteins - Molecular Cell Biology - Ncbi Bookshelf

Section 15.2Overview of Membrane Transport Proteins Very few molecules enter or leave cells, or cross organellar membranes, unaided byproteins. Even transport of molecules, such as water and urea, that can diffuseacross pure phospholipid bilayers is frequently accelerated by transport proteins.The three major classes of membrane transport proteins are depicted in Figure 15-3a . All are integral transmembraneproteins and exhibit a high degree of specificity for the substance transported. Therate of transport by the three types differs considerably owing to differences intheir mechanism of action. Schematic diagrams illustrating action of membrane transportproteins. Gradients are indicated by triangles with the tip pointing toward lowerconcentration, electrical potential, or both. (a) The three major typesof transport proteins. Pumps utilize (more...) ATP-powered pumps (or simply pumps) are ATPasesthat use the energy of ATP hydrolysis to move ions or small molecules across a membrane against a chemical concentration gradient or electricpotential. This process, referred to as activetransport , is an example of a coupled chemical reaction (Chapter 2). In this case, transport ofions or small molecules uphill against a concentrationgradient or electric potential across a membrane, which requires energy, is coupledto the hydrolysis of ATP to ADP and Pi, which releases energy. Theoverall reaction ATP hydrolysis and theuphill movement of ions or smallmolecules is energetically favorable. Such pumpsmaintain the low calcium (Ca2+) and sodium(Na+) ion concentrations inside virtually all animal cellsrelative to that in the medium, and generate the low pH inside animal-celllysosomes, plant-cell vacuoles, and the lumen of the stomach. Channel proteins transport water or specific type Continue reading >>

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