1. Aim: How can we compare carrier mediated and vesicular transport?
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Worksheet
Test on Thursday

2. Share and Pair- Tonicity Problems

3. Carrier Mediated Transport
B- Endocytosis

4. Carrier-Mediated Transport
Carrier-mediated transport of ions and organic substrates
Facilitated diffusion
Active transport
Characteristics
Specificity:
one transport protein, one set of substrates
Saturation limits:
rate depends on transport proteins, not substrate
Regulation:
cofactors such as hormones

5. Carrier-Mediated Transport
Cotransport
Two substances move in the same direction at the same time
Countertransport
One substance moves in while another moves out

6. Carriers and Vesicles
FIGURE 3–18 Facilitated Diffusion.

7. Carrier-Mediated Transport
Facilitated diffusion
Passive
Carrier proteins transport molecules too large to fit through channel proteins (glucose, amino acids):
molecule binds to receptor site on carrier protein
protein changes shape, molecules pass through
receptor site is specific to certain molecules
Membrane Transport: Facilitated Diffusion

9. Sodium-potassium exchange pump9

10. Carrier-Mediated Transport
Active transport
Active transport proteins:
move substrates against concentration gradient
require energy, such as ATP
ion pumps move ions (Na+, K+, Ca2+, Mg2+)
exchange pump countertransports two ions at the same time
Sodium-potassium exchange pump
sodium ions (Na+) out, potassium ions (K+) in
1 ATP moves 3 Na+ and 2 K+

11. Active Transport 1 2 3 4 1 3 Na+ expelled 3 Na+ ADP P 2 K+ imported K+
gradient
Na+
Na+/K+ ATPase
Extra cellular fluid
Cytosol
2K+
ATP 2 3 4
Na+
gradient
3 Na+
Cytosol K+
gradient 1

13. Carriers and Vesicles Vesicular Transport (or bulk transport)
Materials move into or out of cell in vesicles
Endocytosis (endo- = inside) is active transport using ATP:
receptor mediated
pinocytosis
phagocytosis
Exocytosis (exo- = outside)
Granules or droplets are released from the cell

15. Endocytosis Receptor-mediated endocytosis:
Receptors (glycoproteins) bind target molecules (ligands)
Coated vesicle (endosome) carries ligands and receptors into the cell.

16. Carriers and Vesicles Endocytosis Exocytosis Pinocytosis Phagocytosis
Endosomes “drink” extracellular fluid
Phagocytosis
Pseudopodia (psuedo- = false, pod- = foot)
Engulf large objects in phagosomes
Exocytosis
Is the reverse of endocytosis

17. Endocytosis Figure 3–21 Receptor-Mediated Endocytosis.
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18. Exocytosis 18

21. Summary
Distinguish carrier mediated facilitated diffusion and carrier mediated active transport.
Distinguish endocytosis and exocytosis.

22. Carriers and Vesicles
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 22

23. Carriers and Vesicles
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 23

24. Carriers and Vesicles
Figure 3–19 The Sodium–Potassium Exchange Pump