1. Active Transport
Sections 5.5 & 5.6

2. Learning Objectives Describe active transport
Compare & contrast active transport and passive transport
Compare endocytosis and exocytosis
Describe differences between the three types of endocytosis

3. Active Transport
Active transport = the cell uses energy to move molecules against their concentration gradient
ATP provides the energy needed

4. Why Cells Need Active Transport…
Allows cells to maintain homeostasis in a changing environment
Homeostasis = keeping things stable or constant

5. How Active Transport Works
Solute on one side of membrane attaches to the binding site on the transport protein
ATP gives a phosphate group to the transport protein (phosphorylates)
Protein changes shape and release solute to the other side of the membrane
Phosphate group detaches & protein returns to its original shape

7. Examples of Active Transport
Sodium/Potassium pump
Moves 3 sodium ions (Na+) out of the cell and 2 potassium ions (K+) into the cell
Creates an electrochemical gradient that is used to power other transport systems in the cell

8. Sodium/Potassium Pump

9. Proton pump Moves hydrogen ions across the membrane
Builds up a large number of hydrogen ions

10. Transporting Large Molecules
Very large molecules won’t fit through the phospholipids or proteins
Cell uses exocytosis & endocytosis
Types of active transport because moving vesicles requires the cell to use energy

11. Exocytosis
Exocytosis = process of exporting material out of the cell through the use of vesicles
The process:
A vesicle filled with materials moves to the plasma membrane
Vesicle fuses with the plasma membrane
Vesicle’s contents spill out of the cell & the vesicle becomes part of the cell membrane

13. Endocytosis
Endocytosis = process of taking in macromolecules or other particles by forming vesicles from the plasma membrane
3 Types:
Phagocytosis
Pinocytosis
Receptor-mediated endocytosis

14. Phagocytosis Phagocytosis = means “cell eating”
Cell ingests (eats) large solid particles
Steps:
Folds in the plasma membrane surround the particle (or cell)
When the membrane projections touch they fuse together to create a vacuole
Vacuole can then fuse with lysosomes to break down the particle inside

16. Pinocytosis Pinocytosis = means “cell drinking”
Cell takes in drops of liquid containing dissolved molecules
Membrane has many folds or “pockets”
Pockets pinch off into the cytoplasm to form vesicles full of liquid

17. Receptor-Mediated Endocytosis
Receptor-mediated endocytosis = material binds with membrane receptors before being brought in via endocytosis
Main way cells take in macromolecules
Is very specific

18. Steps: Molecules binds to receptors in a coated pit
The pit pinches off to form a coated vesicle in the cytoplasm
Coating breaks away & is recycled
Uncoated vesicle fuses with small compartments called endosomes
Receptors separate from the molecule (ligand) and return to the plasma membrane
Vesicle containing molecule fuses with lysosomes to break down the molecule