Cell Membrane Transport: Active Transport

Question 1

Define Active Transport.

Answer 1

a process that differs from facilitated diffusion in one crucial aspect: it allows solutes to move away from thermodynamic equilibrium

Question 2

Describe the three functions active transport performs in cells and organelles.

Answer 2

1. makes possible the uptake of essential nutrients from the environment or surrounding fluid
2. allows various substances to be removed from the cell or organelle even with a concentration gradient
3. enables the cell to maintain a constant, nonequilibrium intracellular concentration of specific inorganic ions (K+, Na+, Ca+)

Question 3

Describe direct active transport.

Answer 3

the accumulation of solute molecules or ions on one side of the membrane is coupled directly to an exergonic chemical reaction (hydrolysis of ATP)

Question 4

Describe indirect active transport.

Answer 4

requires energy but it depends on the simultaneous transport of solutes, the favourable movement of one solute down its gradient driving the unfavourable movement of the solute up its gradient (symport to antiport)

Question 5

Direct active transport: P-Type ATPases:

Give examples of these types of transport pumps.

Describe this type of pump.

Answer 5

Na⁺/K+ pump is a good example of this type of pump

proteins that are reversibly phosphorylated by ATP as part of the transport mechanism

Question 6

Direct active transport V-type ATPases:

What does the “v” represent?

what does these proteins do?

Answer 6

the “v” stands for vacuole

these are pump proteins that do NOT undergo phosphorylation so they are not inhibited by vanadate, these proteins have two major components, one embedded in the membrane and the other juts out from the membrane surface

Question 7

Direct active transport F-type ATPases:

Where are these proteins found?

What do they do?

Answer 7

found in bacteria, mitochondrion and chloroplasts

these proteins are involved in proton transfer with an integral membrane component called F₀ and a peripheral membrane component called F₁ , they use ATP hydrolysis to pump protons against their electrochemical potential

Question 8

Direct active transport ABC-type ATPases:

Describe what these proteins look like.

What are MDR’s?

Answer 8

There are four subunits to these proteins, two are hydrophobic and embedded in the membrane with the other two are hydrophilic and on the cytoplasmic side of the membrane. The two peripheral sets are where the cassettes that bind ATP

MDR (multi-drug resistant proteins) are proteins that use the energy of ATP hydrolysis to pump hydrophobic drugs out of cells thereby reducing their effectiveness as theraputic agents

Question 9

Indirect active transport:

What is it driven by?

How does it work?

Answer 9

driven by the movement of an ion down its electrochemical gradient

molecules are transported inwards up their electrochemical gradient which is driven by the simultaneous inward movement of either sodium ions or protons