Active Transport - Review

30 Q&A flashcards covering primary and secondary active transport, pumps, and bulk transport based on the notes.

What is active transport?

Movement of molecules or ions uphill against a gradient (chemical, electrical, or pressure) using cellular energy.

What are the two main categories of active transport and how do they differ in energy source?

Primary active transport uses ATP directly; secondary active transport uses energy from existing ion gradients (usually Na+).

What energy drives endocytosis and exocytosis?

ATP.

In the Na+/K+-ATPase pump, how many Na+ ions are pumped out and how many K+ ions in per cycle?

3 Na+ out and 2 K+ in.

Across the Na+/K+-ATPase, what are the extracellular and cytosolic concentrations of Na+ and K+?

Extracellular Na+ high; cytosolic Na+ low; extracellular K+ low; cytosolic K+ high.

Outline the sequence of events in one cycle of the Na+/K+-ATPase.

Cytosolic Na+ binds, ATP phosphorylates the pump, conformational change expels Na+ outside, extracellular K+ binds, phosphate is released, pump returns to original conformation, K+ released inside.

Why is the Na+/K+-ATPase described as electrogenic?

It moves 3 Na+ out for every 2 K+ in, creating a net outward positive current and a membrane potential.

What are PMCA and SERCA, and where are they located?

PMCA is plasma membrane Ca2+-ATPase; SERCA is sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (in the SR membranes, especially in muscle cells).

What is the main function of Ca2+ ATPases?

Maintain a low cytosolic Ca2+ concentration.

What is secondary active transport?

Does not use ATP directly; uses energy from the Na+ gradient to move other substances against their gradients.

Define symport (co-transport) and antiport (counter-transport).

Symport moves substances in the same direction as the driver ion; antiport moves substances in opposite directions.

What is a symporter?

A transporter that moves substances in the same direction as the driver ion (often Na+).

Give an example of a secondary active transport symporter important in kidney and intestine.

Sodium-glucose cotransporter (SGLT), which brings glucose with Na+ into the cell.

How does the sodium-glucose cotransporter function in renal and intestinal epithelia?

It uses the Na+ gradient established by the Na+/K+-ATPase to move glucose against its gradient into the cell.

What are common examples of antiporters in secondary transport?

Na+/Ca2+ exchanger; Na+/H+ exchanger; Cl-/H+ exchanger; Na+/HCO3- exchanger.

What is the role of Na+-Ca2+ counter-transport?

Uses the Na+ gradient to remove Ca2+ from the cytosol.

Why is Na+/H+ exchange important?

It can move large numbers of H+ to help regulate pH of body fluids.

What is bulk transport?

Endocytosis and exocytosis, which require vesicles and energy.

What processes are included in endocytosis?

Phagocytosis, pinocytosis, and receptor-mediated endocytosis.

What is a coated pit in receptor-mediated endocytosis?

A region of the plasma membrane coated with proteins that mediates receptor-mediated uptake.

What occurs during exocytosis?

Secretory vesicles fuse with the plasma membrane to release contents; requires vesicles and energy.

What is the basic mechanism of active transport across cellular sheets?

Active transport on one side of the sheet, followed by diffusion (simple or facilitated) across the opposite side.

What is the role of the Na+/K+ pump in cell volume regulation?

Helps regulate cell volume by maintaining ion balance and osmotic conditions.

How does Na+/K+-ATPase facilitate secondary active transport?

It creates a Na+ gradient that fuels transporters like the Na+-glucose cotransporter to move substrates into cells.

Which organelle contains SERCA pumps?

The sarcoplasmic reticulum in muscle cells.

Which transporter moves Ca2+ into the sarcoplasmic reticulum?

SERCA (Ca2+-ATPase) pumps Ca2+ from cytosol into the SR.

Why is Na+/K+-ATPase essential for establishing membrane potential?

Because its asymmetric Na+/K+ movement generates the electrochemical gradient that underpins the resting membrane potential.