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#cell physiology

2 public questions tagged with this topic.

Membrane Transportation

Which of the following is a voltage-gated sodium channel subunit responsible for sensing membrane potential?

Voltage-gated sodium channels that drive rapid upstroke of action potentials are built from one polypeptide folded into four homologous repeats, each repeat having six transmembrane helices S1 to S6. S1 through S4 cluster peripherally as the voltage-sensing domain, while S5, S6 and the intervening loop dip back into the membrane as P-loop to create the ion conducting pore. The hallmark of voltage sensing resides in S4, which exhibits a repeating pattern Arg-X-X where positively charged arginine or lysine appears every third residue, flanked by hydrophobic side chains. These gating charges sit

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 11: Voltage-Gated Ion Channels and Electrical Properties of Membranes.

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Membrane Transportation

Which ion has the highest intracellular concentration in most animal cells?

Intracellular ion composition is highly asymmetric relative to extracellular fluid actively maintained using ATP to support excitability volume and enzyme function. In most mammalian cells at rest dominant intracellular cation is potassium one thirty to one forty millimolar inside versus four to five outside ten to thirtyfold gradient while sodium inverse ten to fifteen inside versus one forty five outside chloride four to twenty inside versus one ten outside bicarbonate ten inside versus twenty five outside free calcium extremely low one hundred nanomolar inside versus one point two millimola

Ref: Lodish et al., Molecular Cell Biology, 8th ed., Chapter 11: Intracellular Ion Composition – High K+.

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