Chapter 11 Transmembrane Transport of Ions and Small Molecules Chapter 11 Transmembrane Transport of Ions and Small Molecules 111 Overview of Transmembrane Transport 112 Facilitated Transport of Glucose and Water ID: 771107
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Chapter 11 – Transmembrane Transport of Ions and Small Molecules
Chapter 11 – Transmembrane Transport of Ions and Small Molecules 11.1 Overview of Transmembrane Transport 11.2 Facilitated Transport of Glucose and Water 11.3 ATP-Powered Pumps and the Intracellular Ionic Environment 11.4 Nongated Ion Channels and the Resting Membrane Potential 11.5 Cotransport by Symporters and Antiporters 11.6 Transcellular Transport
Transmembrane Transport of Ions and Small Molecules 11.1 Overview of Transmembrane Transport Cellular membranes regulate the traffic of molecules and ions into and out of cells and their organelles. The simple diffusion rate of substance movement across the phospholipid part of a membrane is proportional to its concentration gradient and hydrophobicity. Most molecules, except O 2 and CO 2 , are moved by protein channels and some transporters down their concentrations gradients or by other transporters and ATP-powered pumps up their concentration gradients.
Transmembrane Transport of Ions and Small Molecules 11.2 Facilitated Transport of Glucose and Water Protein-mediated transport is faster than simple diffusion, highly specific, and the transport rate is limited by the number of transporters ( V max ) and transporter affinity ( K m ) for the molecule/ion. Water moves by osmosis across membranes but some membranes have aquaporin water channels to increase rate of water transport. Uniport proteins convert between two conformational states to facilitate diffusion across a membrane.
Transmembrane Transport of Ions and Small Molecules 11.3 ATP-Powered Pumps and the Intracellular Ionic Environment Four classes of transmembrane proteins couple energy released by ATP hydrolysis with energy-requiring transport of substances against their concentration gradients. The combined action of P-class ATP-powered pumps generates the usual ionic milieu of animal cells. ABC superfamily proteins transport a wide array of substrates, including toxins, drugs, phospholipids, peptides, and proteins, into or out of the cell.
Transmembrane Transport of Ions and Small Molecules 11.4 Nongated Ion Channels and the Resting Membrane Potential The animal cell plasma membrane resting potential is generated by the ATP-powered Na + /K + pump and nongated K + channels. The structure and chemical nature of a channel pore lowers the activation energy for passage of a specific ion over other ions, which may be even smaller. Patch-clamping techniques measure ion movements through single channels.
Transmembrane Transport of Ions and Small Molecules 11.5 Cotransport by Symporters and Antiporters Two forces constitute an electrochemical gradient across a membrane – electric potential and ion concentration gradient. Cotransporters use the energy released by ion (H + / Na + ) movement down its electrochemical gradient to power transport of another molecule or different ion up its concentration gradient.
Transmembrane Transport of Ions and Small Molecules 11.6 Transcellular Transport Apical and basolateral plasma-membrane regions of polarized epithelial cells contain different transport proteins whose activities are coordinated to accomplish different transport processes: Transcellular transport of amino acids and glucose from the intestinal lumen to the blood Stomach acid secretion Bone resorption