1. 5.3 Active Transport Across a Membrane
The movement of molecules against their concentration gradient
Movement from low to high concentration
Movement is facilitated by carrier proteins
Requires the expenditure of energy in the form of ATP
Ex: sodium-potassium pump
Uses ATP to move sodium ions out of the cells and potassium ions into the cell against their concentration gradients.

2. The Sodium-Potassium Pump
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
carrier
protein
Outside K+ K+ K+ K+
Na+
Na+
Na+
Na+
Na+
Inside
Carrier has a shape that allows
it to take up 3 Na+

3. The Sodium-Potassium Pump
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
carrier
Outside K+
protein K+ K+ K+ K+ K+ K+ K+
Na+
Na+
Na+
Na+
Na+
Na+
Inside
Na+
Carrier has a shape that allows
it to take up 3 Na+.
Na+ P
ATP
Na+
2. ATP is split, and phosphate
group attaches to carrier

4. The Sodium-Potassium Pump
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
carrier
protein K+
Outside K+ K+ K+ K+ K+ K+ K+
Na+
Na+
Na+
Na+
Na+
Inside
Carrier has a shape that allows
it to take up 3 Na+.
Na+
Na+ P
Na+
ATP
Na+
group attaches to carrier
2. ATP is split, and phosphate K+
Na+
Na+
Na+ K+ K+ K+ P
Na+
Na+
3. Change in shape results and
outside the cell.
causes carrier to release 3 Na+

5. The Sodium-Potassium Pump
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
carrier
protein K+
Outside K+ K+ K+ K+ K+ K+
Na+
Na+ K+
Na+
Na+
Na+
Inside
Na+
1. Carrier has a shape that allows
it to take up 3 Na+.
Na+
Na+ P
Na+
ATP
Na+
2. ATP is split, and phosphate
group attaches to carrier. K+
Na+
Na+
Na+ K+ K+ K+ Na + Na + K + Na + K + P K + K +
Na+
Na+
3. Change in shape results and
causes carrier to release 3 Na+
outside the cell. P
Na+
Na+
allows it to take up 2K+.
4. Carrier has a shape that

6. The Sodium-Potassium Pump
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
carrier
protein K+
Outside K+ K+ K+ K+ K+ K+ K+
Na+
Na+
Na+
Na+
Na+
Na+
Inside
1. Carrier has a shape that allows
it to take up 3 Na+.
Na+
Na+ P
Na+
ATP
Na+
2. ATP is split, and phosphate
group attaches to carrier.
Na+ K+
Na+ K+
Na+
Na+
Na+ K+
Na+ K+ K+ K+ K+ K+
Na+
Na+
Na+ K+
Na+ K+ P P
Na+ K+
Na+ K+
Na+
5. Phosphate group is released
from carrier.
3. Change in shape results and
causes carrier to release 3 Na+
outside the cell. P
Na+
Na+
allows it to take up 2 K+.
4. Carrier has a shape that

7. The Sodium-Potassium Pump
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
carrier
protein K+
Outside K+ K+ K+ K+
Na+
Na+ K+ K+ K+
Na+ K K+
Na+
Na+
Na+
Na+
Na+
Na+
Inside
it to take up 3 Na+.
1. Carrier has a shape that allows
Na+
Na+
Na+ P
Na+
Na+ K+ K+
ATP
Na+
6. Change in shape results and
causes carrier to release 2K+
inside the cell.
2. ATP is split, and phosphate
group attaches to carrier.
Na+ K+
Na+ K+
Na+
Na+
Na+ K+
Na+ K+ K+ K+ K+ K+
Na+
Na+ K+
Na+ K+ P
Na+
Na+ P
Na+ K+ K+
Na+
5. Phosphate group is released
from carrier.
3. Change in shape results and
outside the cell.
causes carrier to release 3 Na+ P
Na+
Na+
4. Carrier has a shape that
allows it to take up 2 K+.

8. Active Transport Across a Membrane
Macromolecules are transported into or out of the cell inside vesicles via bulk transport
Exocytosis – Vesicles fuse with plasma membrane and secrete contents
Endocytosis – Cells engulf substances into a pouch which becomes a vesicle
Phagocytosis – Large, solid material is taken in by endocytosis
Pinocytosis – Vesicles form around a liquid or very small particles
Receptor-Mediated Endocytosis– Specific form of pinocytosis using receptor proteins and a coated pit

9. Exocytosis Plasma membrane Outside Inside secretory vesicle
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Plasma membrane
Outside
Inside
secretory
vesicle

10. Three Methods of Endocytosis
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plasma membrane
paramecium
pseudopod
vacuole
forming
vacuole
399.9 μm
a. Phagocytosis
vesicles
forming
solute
vesicle
b. Pinocytosis
0.5 μm
receptor protein
coated
pit
coated
vesicle
solute
coated vesicle
coated pit
c. Receptor-mediated endocytosis

11. 5.4 Modifications of Cell Surfaces
Cell Surfaces in Animals
Extracellular Matrix (ECM)
Meshwork of proteins and polysaccharides in close connection with the cell that produced them
Collagen – resists stretching
Elastin – provides resilience to the ECM
Integrin – play role in cell signaling
Proteoglycans – regulate passage of material through the ECM to the plasma membrane

12. Animal Cell Extracellular Matrix
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Inside (cytoplasm)
actin filament
integrin
elastin
fibronectin
proteoglycan
collagen
Outside (extracellular matrix)

13. Modifications of Cell Surfaces
Cell Surfaces in Animals
Junctions Between Cells
Adhesion Junctions - Intercellular filaments between cells
Desmosomes – internal cytoplasmic plaques
Tight Junctions – form impermeable barriers
Gap Junctions
Plasma membrane channels are joined (allows communication)

14. Junctions Between Cells of the Intestinal Wall
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
plasma
membranes
cytoplasmic
plaque
Filaments of
cytoskeleton
adhesion
proteins
100 nm
intercellular
space
a. Adhesion junction
plasma
membranes
light junction
proteins
intercellular
space
50 nm
b. Tight junction
plasma
membranes
membrane
channels
intercellular
space
20 nm
c. Gap junction
a: From Douglas E. Kelly, J. Cell Biol. 28 (1966): 51. Reproduced by copyright permission of The Rockefeller University Press; b: © David M. Phillips/Visuals Unlimited; c: Courtesy Camillo Peracchia, M.D.

15. Modifications of Cell Surfaces
Plant Cell Walls
Plants have a freely permeable cell wall, with cellulose as the main component
Plasmodesmata penetrate the cell wall
Each contains a strand of cytoplasm
Allow passage of material between cells

16. Plasmodesmata plasmodesmata cell wall cell wall middle lamella plasma
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
plasmodesmata
cell wall
cell wall
middle lamella
plasma
membrane
plasma
membrane
cell wall
cell wall
cytoplasm
cytoplasm
plasmodesmata
Cell 1
Cell 2
0.3mm
© E.H. Newcomb/Biological Photo Service