Active Transport across the Membrane

Question 1

What is Active Transport?

Answer 1

• The movement of substances across the cell membrane up their concentration gradient
• Requires energy=ATP

Question 2

What does Active Transport & Facilitated Diffusion have in common?

Answer 2

-They both require the selective Carrier proteins

Question 3

What are the 3 types of Carrier Proteins that Active Transport use?

Answer 3

• Uniporters
• Symporters
• Antiporters

Question 4

What is a Uniporter?

Answer 4

-Carrier protein where it transport a single type of molecule

Question 5

What is a Symporter?

Answer 5

-Carrier protein where it transports 2 molecules in the SAME direction

Question 6

What is a Antiporter?

Answer 6

-Carrier protein where it transports 2 molecules in OPPOSITE directions= Sodium-Potassium pump

Question 7

What are the 2 things that Active Transport enables?

Answer 7

• It enables a cell to take up additional molecules of a substance that is already present in the cytoplasm in concentrations higher than the extracellular fluid
• Also enables a cell to move substances out of its cytoplasm & into the extracellular fluid

Question 8

What do most animals have in terms of the concentrations of Na+ & K+?

Answer 8

-They have a low internal concentration of Na+ and a high concentration of K+

Question 9

How do animal cells regulate the concentrations of Na+ & K+?

Answer 9

-They maintain the differences by actively pumping Na+ out of the cell & K+ in the cell

Question 10

How does the Sodium-Potassium Pump work?

Answer 10

-It uses energy stored in ATP to move the Na+ & K+ ions

Question 11

What is the important characteristic of the Sodium-Potassium pump?

Answer 11

-It is an active transport mechanism= transports Na+ & K+ from areas of low to areas of high concentrations

Question 12

What are the 6 steps for the Sodium-Potassium pump?

Answer 12

1) 3 Na+ bind to the cytoplasmic side of the protein
2) ATP phosphorylates (phosphate group is covalently attached to protein) the protein w/ bound sodium
3) Phosphorylation causes change in protein reducing its affinity for Na+, then the Na+ diffuses out
4) The new conformation has high affinity for K+, 2 K+ binds to the exposed sites
5) The binding of K+ causes dephosphorylation of the protein
6) The dephosphorylation of protein triggers change back into original conformation w/ low affinity for K+= diffuses into cell

Question 13

How is ATP used directly & indirectly in Active Transport?

Answer 13

• ATP is used directly in the sodium-potassium pump

- ATP is used indirectly in coupled transport

Question 14

What is Coupled Transport?

Answer 14

• When molecules are moved against their concentration gradient by using the energy in a gradient of a different molecule
• SO the energy is captured & used to move a different molecule against its gradient

Question 15

How does Coupled Transport work?

Answer 15

• A membrane protein transports Na+ into the cell (down its concentration gradient) at the same time it transports a glucose molecule into the cell
• SO the gradient driving the Na+ entry allows sugar molecules to be transported against their gradient
• The Na+ gradient is maintained by the sodium-potassium pump

Question 16

What is the Countertransport?

Answer 16

• The inward movement of Na+ it coupled w/ the outer movement of another substance such as Ca2+ or H+ & bind to the same transport protein
• The cell uses the energy released as Na+ moves down its concentration gradient into the cell to eject the subtance against its concentration gradient

Question 17

What do Countertransport & Cotransport have in common in terms of potential energy?

Answer 17

-The P.E in the concentration gradient of one molecule is used to transport another molecule against its concentration gradient

Question 18

What is the Difference between Countertransport & Cotransport?

Answer 18

-The direction that the second molecule moves relative to the first molecule