3.5.4 Active Transport: The Sodium-Potassium Pump

Question 1

nerve cells (neurons)

Answer 1

• transmit information in the form of electrical signals called action potentials. At rest, neurons actively maintain a polarization across their cell membranes.
  The electrical difference, called potential, stores energy just as batteries do. At rest, nerve cells have a negative charge on the inside relative to their exterior.
• at rest, positively charged potassium ions are permitted to cross the plasma membrane with the help of special membrane proteins called potassium channels. Sodium channels are present, but remain closed at this time. Potassium then moves down its concentration gradient, leaving the cell. Negatively charged organic ions remain in the cell, and the overall charge inside the cell is negative.

Question 2

sodium potassium pump

Answer 2

• responsible for maintaining a balance of ions across the nerve cell’s plasma membrane.

Question 3

ATP

Answer 3

• The sodium potassium pump is a form of active transport and so requires an input of energy in the form of ATP. ATP, the cell’s currency, stores energy in the form of phosphate bonds.

Question 4

action potential

Answer 4

• results from an incoming electrical signal from another neuron. The resulting sequence of events is called
  depolarization. Sodium channels open, enabling sodium ions to move into the cell. Sodium channels close, and more potassium channels open. Potassium ions move outside the cell, thus restoring the resting potential.

Question 5

note

Answer 5

• The action of transport proteins and an expenditure of ATP restore resting potential. Transport proteins have ATP binding sites and recognition sites for the molecules to be transported. The transport protein binds with a sodium ion. ATP donates a phosphate group
  to the transport protein, causing it to undergo a conformational change. The protein transports sodium across the membrane.
• The protein binds to potassium ions from outside of the cell and brings them into the cell. The protein returns to its original conformation and can now accept more sodium. The cycle will continue until all of the potassium is transferred into the cell and resting potential is restored.

Question 6

Which process will transport sodium ions to the outside of the cell and potassium ions to the inside of the cell?

Answer 6

• active transport

Question 7

Transport of sodium out of the cell via the sodium-potassium pump is an example of

Answer 7

• active transport

Question 8

In a resting nerve cell the interior is ______________ relative to the exterior.

Answer 8

• negative

Question 9

A nerve cell membrane is permeable to __________ but impermeable to __________.

Answer 9

• potassium; sodium

Question 10

In order for the resting potential of a neuron to be restored, what must happen?

Answer 10

• Transport proteins must remove sodium ions from the cell and import potassium ions into the cell.