chapter13

What is a membrane pump?

A protein that uses energy (usually ATP) to move substances against their concentration gradient.

What is a secondary transporter?

A transporter that uses the energy from an existing ion gradient (e.g.

What is a membrane channel?

A pore-forming protein that allows specific ions or molecules to pass through the membrane down their gradient.

What is the equation to calculate free energy (ΔG) for a concentration gradient?

ΔG = RT ln(C₂/C₁)

What is the equation for electrochemical energy (ΔG) for charged substances?

ΔG = RT ln(C₂/C₁) + zFΔΨ

What is Ca²⁺-ATPase?

A P-type ATPase that pumps calcium ions out of the cytoplasm into the SR/ER or extracellular space.

What does the Na⁺/K⁺-ATPase do?

Pumps 3 Na⁺ out and 2 K⁺ into the cell

What is a P-ATPase?

A family of ATPases that form phosphorylated intermediates

What are the domains of Ca²⁺-ATPase?

N (nucleotide-binding)

What are the major intermediates in Ca²⁺-ATPase’s cycle?

E1 → E1~P → E2-P → E2

What are the structural components of ABC transporters?

2 transmembrane domains (TMDs) and 2 nucleotide-binding domains (NBDs).

How do ABC transporters function?

Use ATP hydrolysis to transport substances across membranes.

What is an antiporter? Give an example.

A transporter that moves two substances in opposite directions. Example: Na⁺/Ca²⁺ exchanger.

What is a symporter? Give an example.

A transporter that moves two substances in the same direction. Example: Na⁺/glucose symporter.

How do membrane channels select ions?

Via a selectivity filter that fits the ion's size and charge.

How do voltage-gated Na⁺ and K⁺ channels respond to membrane potential?

Voltage sensors trigger opening/closing in response to depolarization; Na⁺ channels inactivate quickly

What is the ball-and-chain model?

A model where a flexible peptide chain blocks a channel’s pore to inactivate it after opening.

How do toxins affect the acetylcholine receptor and acetylcholinesterase?

Toxins like alpha-bungarotoxin block the receptor; sarin inhibits acetylcholinesterase.

Name natural inhibitors of membrane pumps and channels.

Ouabain (Na⁺/K⁺-ATPase)