AQUAPORIN CHANNEL DISCUSSION

Aquaporins

Specialized channels in cellular membranes that rapidly facilitate the movement of water molecules.

Simple Diffusion

The process where water molecules move across the lipid bilayer based on membrane permeability, small molecule size, and low charge.

When were aquaporins discovered?

They were discovered in $1992$, changing the understanding of biological water transport.

How does the speed of water transport in aquaporins compare to simple diffusion?

The flow of water through aquaporins is significantly faster than diffusion through phospholipid bilayers.

In which direction does water move through aquaporins?

Water moves selectively down its concentration gradient (from high concentration to low concentration).

What are two physiological examples that require rapid water transport via aquaporins?

Tear production and saliva production.

Why do red blood cells contain many aquaporins?

To manage intracellular volume and pressure effectively.

Aquaporins

Specialized protein channels that facilitate the rapid and selective movement of water molecules across cellular membranes.

How many membrane-spanning alpha helices do aquaporins have?

Six.

What lines the inner passageway of an aquaporin to stabilize water molecules?

Hydrophilic amino acids.

In what arrangement do water molecules pass through the narrow aquaporin channel?

In a single file.

How do aquaporins prevent protons ($H^+$ ions) from passing through?

Positive charges within the narrow passage create electrostatic repulsion that hinders the passage of cations.

Why is it biologically important to block proton passage through aquaporins?

To prevent the disruption of proton gradients that are essential for ATP production.

Approximately how many water molecules can pass through an aquaporin per second?

Approximately 1 million water molecules.

Do aquaporins require energy (ATP) to transport water?

No, they facilitate water movement down its concentration gradient without using energy.

Are aquaporins found in prokaryotic organisms?

Yes