L7: Membranes - Membrane transport

Question 1

What is active transport?

Answer 1

• Transport against a concentration gradient

- Require input of energy

Question 2

What is an example of active transport?

Answer 2

• Sodium-Potassium pump

Question 3

What is primary active transport?

Answer 3

• Transport that uses energy directly to move molecules against a concentration gradient

Question 4

What is the energy source of secondary active transport?

Answer 4

• Proton gradient (or something else); not ATP

Question 5

What is the FIRST step of secondary active transport?

Answer 5

• Protons (H+) are transported across the membrane by a transporter protein (#1)
• This is active transport (requires ATP)
• Causes a proton gradient (more protons outside the cell)

Question 6

What is the SECOND step of secondary active transport?

Answer 6

• The cell now has established an electrochemical gradient

- NOTE: Protons cannot move back across the membrane due to their charge

Question 7

What is the THIRD step of secondary active transport?

Answer 7

• Transporter protein (#2) allows the movement of H+ down/along the concentration gradient (i.e. back inside the cell)
• The flow of protons back into the cell provides the energy to move another molecule outside the cell. (think “water wheels”)
• The “other” molecule moves AGAINST its own concentration gradient (in this case, lower to higher concentration)