2. Under physiological conditions, the Na*-K+ pump transports sodium and potassi

Question

2. Under physiological conditions, the Na*-K+ pump transports sodium and potassium across the membrane through the hydrolysis of ATP. This occurs in a sequence of steps. A. (5pts) Beginning with the START step, put the other steps a-e (currently listed in random order) of the Na*-K* pump's mechanism in order to complete a full cycle of transport. START - The protein is phosphorylated open to the extracellular side, and contains 2 K ions. a. ATP hydrolysis, protein phosphorylation, and ADP release open the protein to the extracellular side. b. The protein binds ATP which opens the protein to the cytoplasmic side. c. The protein closes & dephosphorylates. d. 3 Na+ exit into the extracellular space, and 2 K+ enter into the protein. e. 2 K* exit into the cytoplasm, 3 Na enter into the protein, and the protein closes. Order of steps: START-C -E -A D B B. (3pts) Describe a condition in which the cycle would proceed in the reverse order.

Explanation / Answer

NA and K pump:

Sodium and potassium ions play a major role in nerve cells.

Nerve impulse:

Resting phase:

During resting phase of the neurons, the K ions pass inside freely than the other ions. It is polarized state.

Action phase:

During active phase, depolarization occurs, which results in the change in the membrane permeability.

Na ions move inside the neurons and overall positive charge inside the neuron is high, which creates nerve impulse.

When enough NA ions have entered the neuron membrane permeability for Na is reduced and K ions move inside till the resting phase is achieved. Again it reaches its polarized state.

This process of polarization and depolarization continues to adjacent nerve cells and the nerve impulse thus travels from one neuron to another.

START ORDER:

b) The protein binds ATP which opens the protein to the cytoplasmic side.

a) ATP hydrolysis, protein phosphorylation, and ADP release open the protein to the extracellular side.

Phosphorylated pump has low affinity towards Na+ and it is released out

d) 3Na+ exit into the extracellular space, and 2K+ enter into the protein.

c) the protein closes and dephosphorylates

Dephosphorylation has high affinity to Na+ ions thus moving inside.

e) 2K+ exit into the cytoplasm, 3NA+ enter into the protein, and the protein closes.

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