ap bio 5.4: Active transport uses energy to move solutes against their gradientsWhat is active transport?

What is active transport

Active transport is the movement of a substance across a cell membrane against its concentration or electrochemical gradient, mediated by specific transport proteins and requiring energy expenditure.

Which proteins are involved in active transport and why?

Carrier proteins are involved because they can pick up solutes and transport them against their concentration gradient, unlike channel proteins that only allow passive movement.

Why does active transport require energy?

Moving solutes against a gradient requires work, and thus energy, to move solutes from areas of lower concentration to areas of higher concentration.

How does ATP power active transport?

ATP transfers a phosphate group to the transport protein, inducing a shape change that moves the solute across the membrane.

What is the sodium-potassium pump?

It’s a transport protein in animal cells that actively moves sodium ions (Na+) out of the cell and potassium ions (K+) into the cell against their concentration gradients.

What happens first in the sodium-potassium pump process?

Sodium ions inside the cell bind to the transport protein.

What role does ATP play in the sodium-potassium pump?

ATP phosphorylates the pump protein, causing it to change shape and move sodium ions outside the cell.

What happens after sodium is released outside the cell?

Potassium ions outside the cell bind to the pump, causing the release of the phosphate group and the protein to return to its original shape.

How are potassium ions moved into the cell?

The protein’s shape change after phosphate release allows potassium ions to enter the cell, completing the cycle.

How does active transport maintain internal concentration gradients in cells?

By continuously pumping sodium out and potassium in, cells keep a high internal K+ concentration and low Na+ concentration relative to their environment.

What is voltage across a cell membrane?

Voltage is the electrical potential energy across a membrane, created by the separation of opposite charges.

Define membrane potential.

Membrane potential is the difference in electrical charge across a cell’s plasma membrane due to the unequal distribution of ions.

Why is membrane potential important in cells?

It influences the movement of all charged substances across the membrane and is crucial for cellular processes like muscle contraction and nerve impulses.

How does membrane potential affect cation and anion transport?

Membrane potential favors passive transport of cations into the cell and anions out of the cell due to charge differences.

What is an electrochemical gradient?

It is the combined force of a concentration gradient (chemical force) and electrical charge gradient across a membrane.

How does an ion move in relation to its electrochemical gradient?

Ions move in a way that balances their concentration gradient and electrical gradient (e.g., Na+ enters the cell driven by both concentration and charge).

What is an electrogenic pump?

It is an active transport protein that generates voltage across a membrane while pumping ions.

What is the main electrogenic pump in animal cells?

The sodium-potassium pump, which creates a net positive charge outside the cell.

What is a proton pump, and where is it commonly found?

A proton pump is an active transport protein that uses ATP to move hydrogen ions (H+) out of the cell, creating a membrane potential. It’s common in plants, fungi, and bacteria.

What dual energy sources does the proton pump generate?

It generates voltage across the membrane and an H+ concentration gradient, which can be used for other processes.

What is cotransport?

Cotransport is when a transport protein couples the “downhill” diffusion of one substance with the “uphill” transport of another substance.

How do plants use cotransport?

Plants use H+ gradients created by proton pumps to actively transport nutrients like sucrose into cells.

How does the H+/sucrose cotransporter work?

The transporter uses the energy of H+ moving down its gradient to bring sucrose into the cell against its gradient.

How does the Na+/glucose cotransporter work in animal intestines?

It moves glucose into cells by coupling it with Na+ moving down its concentration gradient.

What role does osmosis play in Na+/glucose cotransport?

Water follows the transported Na+ and glucose into cells and then into the bloodstream, which helps with hydration in treatments like oral rehydration solutions.