Lecture 3.4: Chapter 12 Transport Across Cell Membranes

This set of flashcards covers key concepts and terminology from Lecture 3.4 on transport across cell membranes, including membrane structure, the mechanisms of transport proteins, and the principles of active and passive transport.

What do cell membranes contain that facilitates the passage of small and water-soluble molecules?

Specialized membrane transport proteins.

What kind of bilayers are impermeable to most water-soluble molecules?

Protein-free, artificial lipid bilayers.

What factors influence passive transport of charged solutes?

Both the concentration gradient and membrane potential.

How do cells prevent osmotic swelling?

By ejected water or using structural components like cell walls.

What is the process called that allows water to move across cell membranes down its concentration gradient?

Osmosis.

What are the two classes of membrane transport proteins found in cells?

Transporters and Channels.

What do transporters and channels facilitate the movement of?

Solutes across membranes.

Inside a typical mammalian cell, what is the concentration of Na+?

5-15 mM.

What is the membrane potential?

The electrical gradient across the membrane.

What characterizes the Na+ pump function in animal cells?

It expels Na+ and brings in K+ using ATP.

What do aquaporins specifically facilitate?

The selective passage of water molecules.

What is the electrochemical gradient composed of?

A concentration gradient and membrane potential.

How does passive transport differ from active transport?

Passive transport occurs spontaneously; active transport requires energy input.

What are ion channels?

Pores formed by proteins that allow specific ions to pass through the membrane.

What role do pumps play in membrane transport?

They actively transport solutes against their electrochemical gradient.

What is a gradient-driven pump?

A pump that uses existing solute gradients to drive active transport.

What happens during the conformational changes of a transporter?

The transporter alternates between states to transfer solutes across the membrane.

Can transport proteins be selective?

Yes, transporters are highly selective for their binding solutes.

What constitutes an osmotic environment?

The environment created by solute concentrations that influence water movement.

In what scenario do channels only transport ions?

When they are in an open conformation.

What does active transport require that passive transport does not?

An input of energy.

How do cells regulate intracellular Ca2+ concentration?

By using Ca2+ pumps to keep cytosolic Ca2+ concentration low.

What is the main energy source for the Na+ pump in animal cells?

ATP hydrolysis.

What does a glucose-Na+ symport do?

Uses the Na+ gradient to actively import glucose into cells.

How do aquaporins facilitate osmotic balance in cells?

By allowing rapid diffusion of water across the plasma membrane.

What characteristic is shared by both symports and antiports?

They are both gradient-driven pumps.

What specific ions are typically involved in the Na+ pump mechanism?

Sodium (Na+) and Potassium (K+).

What do gradient-driven pumps exploit to mediate transport?

Solute gradients.

How do plant cells typically utilize electrochemical gradients?

To drive the transport of solutes using H+ pumps.

What helps maintain the internal acidity of lysosomes and vacuoles?

H+ pumps.

What indicates the directionality of a symport?

Transfers solutes in the same direction.

What defines a uniport in membrane transport?

Facilitates movement of a single solute down its concentration gradient.

What is the primary function of the Na+-K+ ATPase?

Pumps Na+ out of the cell while bringing K+ in.

After transport, what must Na+ be continuously pumped out by?

The Na+ pumps in the basal and lateral membranes.

How does the structure of transporters affect their function?

Their conformations determine the binding sites' accessibility.

How do ligand-gated ion channels operate?

They open in response to specific external signals (ligands).

What type of transmembrane protein can act in contrasting directions?

Antiports.

What is the function of the Ca2+ pump in the sarcoplasmic reticulum?

To restore Ca2+ levels after muscle contraction.

Why is the Na+ concentration outside cells significantly higher than inside?

Due to the action of the Na+ pump.

What happens when an ion channel is closed?

It does not transport ions across the membrane.

How do cells in freshwater environments manage to maintain their volume?

By utilizing contractile vacuoles to remove excess water.

What is the unique feature of the ion concentrations within a cell compared to outside?

They are vastly different.

Which cellular structures typically contain pumps that influence pH?

Lysosomes and vacuoles.

In membrane transport, what is a common characteristic of passive transporters?

They move solutes along their electrochemical gradient.

In what type of cells is gradient-driven glucose transport especially important?

Gut epithelial cells.

How does ATP contribute to membrane transport processes?

It serves as the energy source for pumps.

What defines the electrochemical gradient?

The combined effect of concentration and electric charge across a membrane.

Why are gradient-driven pumps essential for cellular function?

They enable cells to maintain concentration differences necessary for metabolic processes.