Refer to Figure 12-27 in Lehninger. The voltage-gated Na+ channel contains an ac

Question

Refer to Figure 12-27 in Lehninger. The voltage-gated Na+ channel contains an activation gate and an inactivation gate. Place the statements under the component or process that they describe. FIGURE 12-26 VollaRe-gated Na channels of neurons. Sodium channels of different tissues and organisms have a variety of subunits, but only the principal subunit (a-) is essential, (a) The a subunit is a large protein with four homologous domains (I to IV, shown spread out here to illustrate the parts), each containing six transmembrane helices (1 to 6). Helix 4 in each domain (blue) is the voltage sensor; helix 6 (orange) is thought to be the activation gate. The segments between helices 5 and 6, the pore region (red), form the selectivity filter, and the segment connecting domains III and IV (green) is the inactivation gate (b) The four domains are wrapped about a central transmembrane channel lined with polar amino acid residues. The four pore regions (red) come together near the extracellular surface to form the selectivity filter, which is conserved in all Na channels. The filter gives the channel its ability to discriminate between Na and other ions of similar size. The inactivation gate (green) closes (dotted lines) soon after the activation gate opens, (c) The voltage-sensing mechanism involves movement of helix 4 (blue) perpendicular to the plane of the membrane in response to a change in transmembrane potential. As shown at the top, the strong positive charge on helix 4 allows it to be pulfed inward in response to the ms.de-negat.ve membrane potential Vm, Depolarization lessens 1 pull, and helix 4 relaxes by moving outward (bottom). This movement is communicated to the activation gate (orange), including conformational change that open the channel in response to depolarization.

Explanation / Answer

Activation gates: 1.Binding site for gate appears after this gate has opened. As only after the opening of this gate sodium ion mive inside.’

So it determines how long the channel is open.

Transmembrane helix maintains the selectivity of the membrane as it allows only sodium ions to move inside

Inactivation gate: Voltage sensing mechanism As they close as they experience that action potential is high enough and stops the entry of sodium ion.

So it determines how long the channel is open.

Inactivation gate has positively charged transmembrane helix which acts as actual voltage sensor.

And these voltage sensors move out of the membrane due to depolarization of the membrane in order to open the gate again. So helix movement results from changes in membrane polarization.

None of them determines the selectivity of the channel.

None of them are ligand gated. As they are ion gated.

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