Active Transport Basics

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Questions and Answers

Which of the following statements accurately describes active transport?

Active transport is non-directional and can move molecules in any direction.

Active transport is used to move solutes against a concentration gradient, away from equilibrium. (correct)

Active transport is a passive process that requires no energy input.

Active transport moves molecules down a concentration gradient, towards equilibrium.

Facilitated diffusion and active transport are both forms of passive transport.

False (B)

What are the four types of transport ATPases involved in direct active transport?

The four types of transport ATPases involved in direct active transport are: P-type, V-type, F-type, and ABC-type.

V-type ATPases pump _____ into organelles such as vacuoles, vesicles, lysosomes, endosomes, and the Golgi complex.

protons Signup and view all the answers

Match the following types of transport ATPases with their primary function:

P-type = Na+/K+ pump V-type = Proton pumps in organelles F-type = Proton pumps, including ATP synthases ABC-type = Transport of a wide variety of molecules across membranes Signup and view all the answers

Which of the following statements accurately describes the effect of membrane potential on the ΔG of calcium ion import?

A negative membrane potential makes ΔG more negative, favoring calcium import. (D) Signup and view all the answers

The Faraday constant (F) is always negative.

False (B) Signup and view all the answers

What is the equation used to calculate the ΔG of ion transport, taking both concentration gradient and membrane potential into account?

ΔG = RTln(C2/C1) + zFVm Signup and view all the answers

For a typical cell with a negative Vm, inward movement of ______ is favored due to the membrane potential.

cations Signup and view all the answers

Match the following terms with their correct definitions:

z = Charge of the solute F = Faraday constant Vm = Membrane potential ΔG = Change in Gibbs free energy Signup and view all the answers

Which of the following is NOT true regarding the E1 conformation of the Na+/K+ pump?

It is open to the outside of the cell. (D) Signup and view all the answers

The Na+/K+ pump uses the energy from ATP hydrolysis to move sodium ions into the cell and potassium ions out of the cell against their concentration gradients.

True (A) Signup and view all the answers

What is the primary reason why the Na+/K+ pump requires energy to function?

Because it moves both Na+ and K+ ions against their concentration gradients, which is energetically unfavorable. Signup and view all the answers

The Na+/K+ pump is an example of ______ active transport, where energy is directly derived from ATP hydrolysis.

primary Signup and view all the answers

Which of the following is true about indirect active transport?

It is driven by ion gradients established by primary active transport. (D) Signup and view all the answers

The uptake of glucose in the intestinal lining cells always occurs by facilitated diffusion.

False (B) Signup and view all the answers

Explain how the Na+/K+ pump indirectly contributes to the uptake of glucose in intestinal cells.

The Na+/K+ pump maintains a high concentration of sodium ions outside the cell, creating a driving force for the Na+/glucose symporter to move glucose into the cell. Signup and view all the answers

The ΔG of transport for uncharged solutes depends only on the ______ across the membrane.

concentration gradient Signup and view all the answers

Which of the following factors influences the ΔG of transport for charged solutes?

Both concentration gradient and membrane potential (C) Signup and view all the answers

Study Notes

Active Transport: Protein-Mediated Movement Up the Gradient

Facilitated diffusion moves molecules down a concentration gradient, towards equilibrium. It's important but only accounts for movement down the gradient.
Active transport moves solutes up a concentration gradient, away from equilibrium. This process requires energy.
Diffusion is nondirectional, while active transport has inherent directionality.

The Coupling of Active Transport to an Energy Source

Direct active transport couples to an exergonic chemical reaction, most often ATP hydrolysis. This reaction drives the transport of substances across the membrane.
Indirect active transport couples the transport of a solute to the movement of an ion (e.g., protons) down its electrochemical gradient.

Direct Active Transport ATPases

Four types of transport ATPases are identified: P-type (e.g., Na+/K+ pump), V-type ("vacuole" H+ pumps), F-type (also H+ pumps, ATP synthases), and ABC-type.
These types differ in structure, mechanism, location, and roles.

V-Type ATPases

V-type ATPases pump protons into organelles like vacuoles, vesicles, lysosomes, endosomes, and the Golgi complex.
They consist of two multi-subunit components: an integral component embedded in the membrane and a peripheral component projecting out.

Direct Active Transport: The Na+/K+ Pump

In a mammalian neuron, the potassium concentration inside is about 30 times higher than outside, and the sodium concentration inside is much lower (around 0.08 times) than outside.
These electrochemical potentials are critical for coupled transport and nerve impulse transmission.

The Na+/K+ Pump is an Allosteric Protein

The Na+/K+ pump exists in two conformational states (E1 and E2).
E1 is open to the inside of the cell and has a high affinity for Na+ ions.
E2 is open to the outside of the cell and has a high affinity for K+ ions.

Requirement for Energy

Pumping Na+ and K+ ions against their concentration gradients requires energy.
The Na+/K+ ATPase uses ATP hydrolysis to drive this transport.
This pump is critical for the asymmetric distribution of ions across the cell membrane of animal cells.

Indirect Active Transport is Driven by Ion Gradients

Indirect active transport (secondary active transport) doesn't directly use ATP hydrolysis.
Movement of molecules up their electrochemical gradients is often coupled to the inward movement of Na+ (in animals) or protons (in plants, fungi, bacteria) which move down their gradient.

Symport Mechanisms of Indirect Active Transport

Many cells pump sodium ions or protons out of the cell (e.g., Na+/K+ pump in animals).
The resulting high extracellular concentration of Na+ facilitates the uptake of other substances (like sugars and amino acids), indirectly powering this process.

Indirect Active Transport: Sodium Symport Drives the Uptake of Glucose

Glucose transport often happens via facilitated diffusion.
In some cells, a Na+/glucose symporter drives glucose uptake even when glucose concentrations are lower outside the cell. This symporter uses the electrochemical gradient of Na+ to move glucose into the cell.

The Energetics of Transport

Every transport event in a cell requires energy input.
For uncharged solutes, only the concentration gradient matters.
For charged solutes, both the concentration gradient and the electrical potential are involved.

For Uncharged Solutes

The change in Gibbs free energy (ΔG) for transport of uncharged solutes depends solely on the concentration gradient.
The formula for calculating inward transport is provided in the notes.

For Charged Solutes

Transport of charged solutes involves the consideration of both the concentration gradient and the membrane potential (Vm).
The membrane potential usually makes inward movement of cations more favorable.
The formula for calculating the change in Gibbs free energy of transport for ions is given in the notes.

Examples (Lactose and Chloride Intake)

The notes include specific examples concerning lactose and chloride ion uptake, demonstrating the energy requirements, and calculations.

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Description

This quiz covers the fundamentals of active transport, highlighting its role in moving molecules against a concentration gradient and its dependence on energy sources like ATP. It discusses the mechanisms of direct and indirect active transport and the different types of ATPases involved in the process.