ATP-Driven Pumps and Active Transport

25 question-and-answer flashcards on ATP hydrolysis, sodium-potassium ATPase, other ion pumps, primary vs. secondary active transport, and related physiological concepts.

What ion gradients does the sodium-potassium ATPase maintain?

High extracellular Na⁺ and high intracellular K⁺ by pumping 3 Na⁺ out and 2 K⁺ in against their gradients.

How many ions are moved per cycle of the Na-K pump and in what directions?

3 Na⁺ are pumped out of the cell and 2 K⁺ are pumped into the cell.

Why does the Na-K ATPase contribute to the resting membrane potential?

It exports more positive charge (3 Na⁺) than it imports (2 K⁺), leaving the outside more positive and the inside slightly negative.

Why is the sodium-potassium pump classified as an "ATPase"?

Because it is an enzyme that catalyzes ATP hydrolysis (and, in reverse, ATP synthesis).

What are the products of ATP hydrolysis?

ADP + inorganic phosphate (Pi) + released energy.

Why are the three phosphates of ATP likened to a loaded spring?

Their negative charges repel; breaking a phosphate bond releases stored energy.

Which form of cellular energy is provided by ATP hydrolysis?

Chemical energy.

Define primary vs. secondary active transport.

Primary uses ATP directly; secondary uses kinetic energy from ions moving down gradients created by primary active transport.

Name a primary active transporter besides the Na-K pump.

Calcium ATPase (Ca²⁺ pump).

What does the Ca²⁺ ATPase do in muscle cells?

Uses ATP to pump Ca²⁺ from the cytoplasm back into the sarcoplasmic reticulum, enabling muscle relaxation.

Which pump secretes acid into the stomach lumen?

The H⁺-K⁺ ATPase (proton pump) in parietal cells.

How do proton pump inhibitors lower stomach acidity?

They block the H⁺-K⁺ ATPase, reducing H⁺ secretion into the gastric lumen.

How does the Na-K pump help regulate cell volume?

By exporting more solutes (3 Na⁺) than it imports (2 K⁺), it limits intracellular osmotic pressure and prevents swelling.

What happens to Na-K pump activity when a cell swells?

Pump activity increases, expelling additional Na⁺ so that water follows out, restoring volume.

What is ATP condensation by the Na-K ATPase?

Synthesis of ATP from ADP + Pi using kinetic energy when Na⁺ and K⁺ move down their gradients (pump running in reverse).

What energy drives the sodium-glucose transporter (SGLT) in the nephron?

Kinetic energy from Na⁺ moving down its gradient into the cell.

In which direction do SGLT move Na⁺ and glucose?

Both Na⁺ and glucose enter the cell (symport).

Why must the Na-K ATPase be active for the SGLT to operate continuously?

It maintains the Na⁺ gradient that provides the kinetic energy for glucose uptake.

What is the sodium-calcium exchanger (NCX) and where is it crucial?

An antiporter in cardiac muscle that uses Na⁺ influx to drive Ca²⁺ efflux against its gradient.

What names are given to transporters moving substances in the same vs. opposite directions?

Symporter (same direction) and antiporter (opposite directions).

What two main energy forms are most used by human cells?

Chemical energy (ATP) and kinetic energy (movement of ions/molecules down gradients).

In gastric physiology, what is meant by a "proton"?

A hydrogen ion (H⁺).

How do ion distributions create the resting membrane potential?

High extracellular Na⁺ and high intracellular K⁺, plus unequal charge movement by the Na-K pump, leave the inside of the cell negatively charged relative to the outside.

Why is water said to "chase solutes" across a membrane?

Osmosis causes water to move toward the compartment with the higher solute concentration.

What feature of the Na-K pump lets it build both chemical and electrical gradients?

It exchanges unequal numbers of positively charged ions (3 out, 2 in) while using ATP.