Active Membrane Transport and Vesicular Processes in Cells

What are the two major active membrane transport processes?

Active transport and vesicular transport.

Why do active transport processes require ATP?

To move solutes across a plasma membrane when they are too large, not lipid soluble, or cannot move down their concentration gradient.

What are carrier proteins in active transport?

Proteins that bind specifically and reversibly with the substance being moved.

What is the difference between antiporters and symporters?

Antiporters transport one substance into the cell while transporting a different substance out; symporters transport two different substances in the same direction.

What is primary active transport?

The process where energy from ATP hydrolysis is used directly to move solutes against their concentration gradient.

What is secondary active transport?

The process where energy is obtained indirectly from ionic gradients created by primary active transport.

What is the role of the Na+-K+ pump?

It pumps sodium out of the cell and potassium into the cell against their concentration gradients.

How does the Na+-K+ pump maintain electrochemical gradients?

By pumping Na+ out and K+ in, which is essential for muscle and nerve function.

What happens during the binding of Na+ to the Na+-K+ pump?

Three cytoplasmic Na+ bind to the pump protein, promoting ATP hydrolysis.

What occurs after ATP hydrolysis in the Na+-K+ pump mechanism?

The pump is phosphorylated, causing a shape change that expels Na+ outside the cell.

What triggers the release of phosphate in the Na+-K+ pump?

The binding of K+ to the pump after Na+ has been expelled.

What is the significance of the Na+-K+ pump in nerve and muscle cells?

It is crucial for maintaining the resting membrane potential and facilitating action potentials.

What is the daily pumping rate of the Na+-K+ pump?

It pumps approximately 30-35% of daily ATP usage.

What is the function of leakage channels in membranes?

They allow Na+ to leak into the cell and K+ to leak out, both down their concentration gradients.

What is the concentration of Na+ outside the cell compared to inside?

There are about 3 million Na+ outside for every 1 million Na+ inside.

What is the concentration of K+ inside the cell compared to outside?

There are about 2 million K+ inside for every 1 million K+ outside.

What is the main energy source for the Na+-K+ pump?

ATP (adenosine triphosphate).

What type of transport is the Na+-K+ pump classified as?

Primary active transport.

What is the overall effect of the Na+-K+ pump on ion concentrations?

It creates a higher concentration of Na+ outside the cell and a higher concentration of K+ inside the cell.

What is the primary role of ATP in active transport?

To provide the energy needed to move solutes against their concentration gradients.

What is the importance of maintaining electrochemical gradients?

It is essential for the proper functioning of excitable tissues like nerves and muscles.

What happens to the Na+-K+ pump after K+ is released inside the cell?

The pump resets to its original conformation, ready to bind Na+ again.

What is the sodium-potassium pump?

An enzyme called Na+-K+ ATPase that pumps Na+ out of the cell and K+ back into the cell.

Where is the sodium-potassium pump located?

In all plasma membranes, especially active in excitable cells like nerves and muscles.

What type of transport is the sodium-potassium pump an example of?

Active transport.

How does sodium influence the transport of other molecules into the cell?

Low Na+ concentration inside the cell strengthens sodium's drive to enter, dragging other molecules with it through carrier proteins.

What are symporters?

Carrier proteins that transport sodium along with other molecules into the cell.

What types of substances are typically transported via secondary active transport?

Sugars, amino acids, and ions.

What is vesicular transport?

Transport of large particles, macromolecules, and fluids across membranes in vesicles.

What energy source is required for vesicular transport?

Cellular energy, usually ATP.

What is endocytosis?

Transport into the cell, involving the formation of protein-coated vesicles.

What are the three types of endocytosis?

Phagocytosis, pinocytosis, and receptor-mediated endocytosis.

What occurs during phagocytosis?

The cell engulfs a large particle by forming a pseudopod around it, enclosing it in a phagosome.

What is pinocytosis?

A type of endocytosis referred to as 'cell drinking' that brings extracellular fluid and solutes into the cell.

What is receptor-mediated endocytosis?

Endocytosis involving specific molecules binding to receptors, allowing selective uptake.

What are caveolae?

Small pits that capture specific molecules and use transcytosis, differing from clathrin-coated pits.

What is exocytosis?

The process of ejecting material from the cell, usually activated by cell-surface signals.

What triggers exocytosis?

The docking of v-SNARE proteins on secretory vesicles with t-SNARE proteins on the target membrane.

What types of substances are commonly exocytosed?

Hormones, neurotransmitters, mucus, and cellular wastes.

What is transcytosis?

Transport into, across, and then out of a cell.

What happens to vesicles after endocytosis?

They may fuse with lysosomes for digestion or undergo transcytosis.

What is the role of receptors in endocytosis?

They allow selective uptake of substances that can bind to them.

How does the sodium-potassium pump create a concentration gradient?

By actively transporting Na+ out of the cell and K+ into the cell, creating a steep gradient.

What is the significance of the sodium gradient created by the sodium-potassium pump?

It drives the entry of sodium into the cell, which can help transport other molecules.

What is the difference between primary and secondary active transport?

Primary active transport directly uses ATP to create a gradient, while secondary active transport uses the gradient created by primary transport.

What is the function of clathrin in receptor-mediated endocytosis?

Clathrin coats the pits that internalize receptors and bound substances.

What is the fate of substances taken up by receptor-mediated endocytosis?

They may be released inside the cell or digested in a lysosome.

Still learning (5)

You've started learning these terms. Keep it up!