Membrane Transport and Facilitated Diffusion Lecture Review

Flashcards covering key concepts of membrane transport, including passive transport (diffusion, osmosis, facilitated diffusion), and active transport (pumps, cotransport, exocytosis, endocytosis).

What is selective permeability?

The property of cell membranes that regulates what enters and exits the cell, creating and maintaining concentration gradients of solutes due to its hydrophobic interior.

What are the two main types of transport across a membrane?

Passive transport and active transport.

What is passive transport?

The transport of a molecule that does not require energy from the cell because a solute is moving with its concentration or electrochemical gradient.

Name three examples of passive transport.

Diffusion, osmosis, and facilitated diffusion.

Explain the process of diffusion.

A spontaneous process resulting from the constant motion of molecules, where substances move from a high to low concentration (down the concentration gradient).

What is osmosis?

The diffusion of water down its concentration gradient across a selectively permeable membrane, or from areas of low solute concentration to areas of high solute concentration.

What is facilitated diffusion?

The diffusion of molecules through the membrane via channel or carrier proteins, without requiring energy, as molecules still move down their concentration gradient.

What are channel proteins?

Proteins that form an open pore or channel in the membrane, primarily moving charged ions, and are often regulated by 'gates' that open or close in response to stimuli.

How is the direction of flow determined for channel proteins?

By the electrochemical gradient (concentration and charge).

What are aquaporins?

Specialized channel proteins for water.

What are carrier proteins?

Proteins that alternate between two conformations to transport large polar molecules like glucose, amino acids, and nucleosides across the membrane.

What is active transport?

The transport of a molecule that requires energy because it moves a solute against its concentration gradient.

What is the primary energy source used by cells for active transport?

Adenosine Triphosphate (ATP), which can transfer its terminal phosphate group to a transport protein, causing a conformational change.

What is membrane potential and what is its role in active transport?

Membrane potential is the electrical charge resulting from unequal concentrations of ions across the membrane, with the cytoplasm being relatively negative; energy is stored in these electrochemical gradients.

What are electrogenic pumps?

Proteins that generate voltage across membranes, which can then be used as an energy source for cellular processes.

Describe the action of the sodium-potassium pump.

It pumps 3 Na+ ions out of the cell and 2 K+ ions into the cell, resulting in a +1 net charge to the extracellular fluid.

What is a proton pump?

An integral membrane protein used by plants, fungi, and bacteria that pumps H+ out of the cell, building up a proton gradient across the membrane.

What is cotransport?

The coupling of a favorable movement (downhill diffusion) of one substance with an unfavorable movement (uphill transport) of another substance, using energy stored in electrochemical gradients.

How do plants use cotransport for sucrose uptake?

Sucrose travels into a plant cell against its concentration gradient only if it is coupled with H+ that is diffusing down its electrochemical gradient via a sucrose-H+ cotransporter.

What is exocytosis?

The secretion of molecules via vesicles that fuse to the plasma membrane, releasing their contents to the extracellular fluid (e.g., nerve cells releasing neurotransmitters).

What is endocytosis?

The uptake of molecules from vesicles formed from the plasma membrane, where the cell membrane folds inward to form a vesicle that pinches off and moves into the cell.

What are the three main types of endocytosis?

Phagocytosis, pinocytosis, and receptor-mediated endocytosis.

Describe phagocytosis.

When a cell engulfs particles by surrounding them with pseudopodia and packaging them into a food vacuole, which then fuses with a lysosome for digestion.

What is pinocytosis?

The nonspecific uptake of extracellular fluid containing dissolved molecules.

What is receptor-mediated endocytosis?

The specific uptake of molecules via solute binding to receptors on the plasma membrane, allowing the cell to take up large quantities of a specific substance by clustering in a coated vesicle.