Question

A) How do potassium leak channels help maintain the inside-negative electrical potential of 50-70 mV across the plasma membrane of the cells?

B) Where in the cell does a protein end up if it does not have a signal sequence?

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Thanks!

Answer 1

A) Extracellular and intracellular fluid of neurons contains ions like sodium, potassium, and chloride and movement of these ions creates an electrical activity across the neural membranes. The resting potential is -70 mv in the inside of membrane and is defined as the inactive axon’s difference. And it must be note that potassium ions and anions is more in the intracellular fluid and on the other hand, sodium and chloride ions are more in the extracellular fluid. Because of the presence of anions the charge of inside the membrane is negative. At the resting state, there is no sodium ions flow. The action potential is short-lived but it makes a large difference in the polarity of the membrane. During action potential time, the voltage across the membrane reverses causing in more positive charge in the intracellular side than other side. This quick change in the polarity effects dropping potential to -50mv. The process of action potential is occur in 4 steps;

i) Threshold of excitation

Stimulation causes the opening of sodium channels, causing the flow of sodium ions into inside of neuron. And if the stimulation go beyond 5 to 15 mv, threshold of excitation from -70 to -65 mv state will occur.

ii) Action potential

It is the reversal of polarity across the membranes.

iii) Depolarization

It is the decrease in the charge across the membranes in few seconds.

iv) Hyperpolarization

It happens during the extra efflux of potassium ions for milliseconds The figure of action potential is given below:

B) If the protein does not have signal sequence, it will remain in the cytoplasm and does not go to anywhere in the cell. Because, signal sequence is like the address to which site the ‘message’ that is protein should deliver. If it does not hold an address, where it can go?