For example, for most sensory modalities sensory cells act as energy transducers, transforming the energy of the environmental stimulus into a change in the electrical potential difference across a biological membrane. Bacteriorhodopsin (bR) is an integral protein in the plasma membrane of a bacterium. Upon light absorption, bR transports protons across the membrane, converting the photon energy into the energy of a proton electrochemical gradient. bR is a single small protein and is the simplest known active ion pump and biological light energy transducer. Consequently, bR is a prototype system for studying the basic steps and rules of biological energy transduction. Energy transduction is thus the fundamental physical basis of the sensory response of most biological systems to their environments. Within each of the evolved sensory modalities there exists an enormous variety of structure and function produced by evolutionary pressures. Rhodopsins are found in one of the GPCR families .
Oxidative phosphorylation within the mitochondrion is another form of energy transduction, as is the conversion of chemical energy to muscle contraction and relaxation.
• A • adhesion • C • cell membranes • cellular adhesion molecules • cellular signal transduction • centrioles • chemotaxis • chloroplast • cilia • communication • concentration gradients • cytokine receptors • cytoplasm • cytoskeleton • E • energy transducers • endoplasmic reticulum • endosomes • exosome • G • Golgi apparatus • GPCRs • H • hormones • I • ion channels • L • lysosome • M • meiosis • microtubules • mitosis • mitochondrion • N • Nitric Oxide • neurotransmission • neuronal interconnections • nuclear membrane • nuclear pore • P • pinocytosis • proteasome • pumps • R •receptor proteins • receptor-mediated endocytosis • S • second messengers • signaling gradients • signal transduction • spindle • structure • T • transport • two-component systems • V • vacuole • vesicle •
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