3.2.3(.2) - Exchange: Active Transport

How does active transport work?

• Molecule attaches to carrier protein

• Protein changes shape → moves molecule across membrane

• Molecule released on other side

Active transport involves ____ proteins

carrier

Differences between active transport and facilitated diffusion

1. Active transport usually moves solutes from low to high conc.
   Facilitated diffusion always moves them from high to low conc.

2. Active transport requires energy - facilitated diffusion doesn’t

How is ATP used in active transport?

ATP undergoes hydrolysis reaction, splitting into ADP + Pᵢ

→ releases energy so solutes can be transported

Active transport of calcium

Co-transporters

• Type of carrier protein

• Bind two molecules a time

• Conc. gradient of one of the molecules is used to move other molecule against its own conc. gradient

  • Diagram shows sodium ions moving into cell down conc. gradient

    → this moves glucose into cell, against its conc. gradient

How does speed of individual carrier proteins affect rate of active transport?

The faster they work, the faster the rate of active transport

How does number of carrier proteins affect rate of active transport?

More proteins = faster rate of active transport

How does rate of respiration affect rate of active transport?

If respiration is inhibited, won’t be any ATP → active transport can’t take place

Why is co-transport needed in the ileum?

In ileum, glucose conc. is too low for glucose to diffuse out of blood

→ glucose is absorbed from lumen of ileum by co-transport

Co-transport of glucose in ileum

1. Sodium ions are actively transported out of ileum epithelial cells, into blood, by Na-K pump

   → creates conc. gradient - now there’s higher conc. of Na⁺ in lumen of ileum than inside cell

2. Causes Na⁺ to diffuse from lumen of ileum into epithelial cell, down conc. gradient, via sodium-glucose co-transporter proteins

3. Co-transporter carries glucose into cell with sodium

   → glucose conc. inside cell increases

4. Glucose diffuses out of cell, into blood, down conc. gradient, through protein channel by facilitated diffusion