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Published byWilfrid Hawkins Modified over 8 years ago
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Alberts • Johnson • Lewis • Morgan • Raff • Roberts • Walter
da Alberts • Johnson • Lewis • Morgan • Raff • Roberts • Walter Molecular Biology of the Cell Sixth Edition con integrazioni e modifiche Chapter 11 Membrane Transport of Small Molecules and the Electrical Properties of Membranes Copyright © Garland Science 2015
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MEMBRANE TRANSPORT
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Ion concentration is different inside and outside cells
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Synthetic lipid bilayers have different permeability to different classes of molecules
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Permeability coefficients of different molecules are very different
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The two main classes of membrane transport proteins are: transporters and channels
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Transport across membranes can be:
Passive or Active
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The electrochemical gradient affects ion transport
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TRANSPORTERS
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Conformational changes of a transporter can mediate passive transport
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Transporter-mediated diffusion reaches a maximum
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Active transport is carried out in three main ways
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Transporters can transfer one ion or two ions, in the same or in the opposite direction
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Glucose transport is driven by Na gradient
Ion gradients represent an energy source
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Glucose crosses the intestinal epithelium
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There are three types of ATP-driven pumps
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ER calcium pump is a P-type transporter
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Na-K ATPase is also a P-type pump
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ABC transporters are the largest family of membrane transport proteins
REM: MDR
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CHANNELS
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Water crosses the membrane through channels: the aquaporins
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Channels can have a closed or open conformation
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Channels can be regulated by several mechanisms
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Ion distribution determines membrane potential
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Channel structure determines ion selectivity
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Mechanosensitive channels open and close
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Ion transport is fundamental for nerve cell function
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Sodium channels have a key role in the generation of a membrane potential
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Individual ion channels can be monitored by patch clamp
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Release of neurotransmitter occurs at synapses
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Various channels are activated in sequence at the neuromuscular junction
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Single neurons are complex computation devices
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THE END
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