Membrane transport active

There are, however, various types of active transport systems, involving protein carriers and known as uniports, symports, and antiports as indicated in Figure 3.7. Thus, symports and antiports involve the transport of two different molecules in either the same or a different direction. Uniports are carrier proteins, which actively or passively (see section "Facilitated Diffusion") transport one molecule through the membrane. Active transport requires a source of energy, usually ATP, which is hydrolyzed by the carrier protein, or the cotransport of ions such as Na+ or H+ down their electrochemical gradients. The transport proteins usually seem to traverse the lipid bilayer and appear to function like membrane-bound enzymes. Thus, the protein carrier has a specific binding site for the solute or solutes to be transferred. For example, with the Na+/K+ ATPase antiport, the solute (Na+) binds to the carrier on one side of... 

Transport across biological membranes is classified according to the thermodynamics of the process. Passive transport is a thermodynamically downhill process the species move toward the equilibrium. The driving force for the passive transport is the potential difference between the two sides of the membrane. Active transport is a thermodynamically uphill process, it is coupled to a chemical reaction and is driven by it. The following transport mechanisms have been recognized ... 

Buchanan, S. K., Smith, B. S., Venkatramani, L., Xia, D., Esser, L., Palnitkar, M., Chakraborty, R., van der Helm, D., and Deisenhofer, J. (1999). Crystal structure of the outer membrane active transporter FepAfrom Escherichia coli. Nat. Struct. Biol. 

Proteins in membranes may function as transporters, to allow or actively encourage molecules to pass through the membrane. Active transport can maintain a flow against a concentration gradient. 

Markin, V. S. Tsong, T. Y. Reversible mechanosensitive ion pumping as a part of mechanoelectrical transduction. Biophys. J. 59, 1317-1324. Markin, V. S. Tsong, T. Y. Frequency and concentration windows for the electric activation of a membrane active transport system. Biophys. J. 59, 1308-1316. 

Membrane BioafiRnity (signal amplification) Receptor induced reaction opening of ion channel invokingthe flux of ions across the membrane Active transport by means of membrane-transport proteins Conductometric, amperometric, potentiometric Potentiometric... 

SRIP). Many laboratories extensively characterized this family of proteins with a battery of diverse techniques, because they provide excellent model systems for the two fundamental functions of membranes active transport and sensory signaling. Twenty-nine variants of BR, HR, SRI, and SRII were documented in related extremely halophlHc archaea, such as Natronomonas pharaonis and Haloarcula vallismortis. Members of the archaeal rhodopsin family were generally assumed to be only in the haloarchaea and appeared to be restricted to the extreme halophilic environments of solar evaporation ponds and other regions of near-saturated salt concentration. 

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