1. Active Transport Processes
Cell Physiology
Active Transport Processes

2. Active Processes Sometimes called solute pumping
Requires protein carriers to transport substances that:
May be too large to travel through membrane channels
May not be lipid-soluble
May have to move against a concentration gradient
ATP is used for transport
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3. Active Processes Active transport
Amino acids, some sugars, and ions are transported by protein carriers known as solute pumps
ATP energizes solute pumps
In most cases, substances are moved against concentration (or electrical) gradients
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4. Active Processes
Example of active transport is the sodium-potassium pump
Sodium is transported out of the cell
Potassium is transported into the cell
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5. Figure 3.11 Operation of the sodium-potassium pump, a solute pump.
Slide 1
Extracellular fluid
Na+
Na+ K+
Na+-K+ pump
Na+
Na+
Na+ K+ P P K+
ATP
Na+ 1 2 3 K+
ADP
Binding of cytoplasmic Na+ to the pump protein stimulates phosphorylation by ATP, which causes the pump protein to change its shape. 1 2
The shape change expels Na+ to the outside. Extracellular K+ binds, causing release of the phosphate group.
Loss of phosphate restores the original conformation of the pump protein. K+ is released to the cytoplasm, and Na+ sites are ready to bind Na+ again; the cycle repeats. 3
Cytoplasm

6. Figure 3.11 Operation of the sodium-potassium pump, a solute pump.
Slide 2
Extracellular fluid
Na+-K+ pump
Na+
Na+ P
ATP
Na+ 1
ADP
Binding of cytoplasmic Na+ to the pump protein stimulates phosphorylation by ATP, which causes the pump protein to change its shape. 1
Cytoplasm

7. Figure 3.11 Operation of the sodium-potassium pump, a solute pump.
Slide 3
Extracellular fluid
Na+
Na+ K+
Na+-K+ pump
Na+
Na+
Na+ K+ P P
ATP
Na+ 1 2
ADP
Binding of cytoplasmic Na+ to the pump protein stimulates phosphorylation by ATP, which causes the pump protein to change its shape. 1
The shape change expels Na+ to the outside. Extracellular K+ binds, causing release of the phosphate group. 2
Cytoplasm

8. Figure 3.11 Operation of the sodium-potassium pump, a solute pump.
Slide 4
Extracellular fluid
Na+
Na+ K+
Na+-K+ pump
Na+
Na+
Na+ K+ P P K+
ATP
Na+ 1 2 3 K+
ADP
Binding of cytoplasmic Na+ to the pump protein stimulates phosphorylation by ATP, which causes the pump protein to change its shape. 1
The shape change expels Na+ to the outside. Extracellular K+ binds, causing release of the phosphate group. 2
Loss of phosphate restores the original conformation of the pump protein. K+ is released to the cytoplasm, and Na+ sites are ready to bind Na+ again; the cycle repeats. 3
Cytoplasm

9. Active Processes
Vesicular transport: substances are moved without actually crossing the plasma membrane
Exocytosis
Endocytosis
Phagocytosis
Pinocytosis
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10. Active Processes Vesicular transport (continued) Exocytosis
Moves materials out of the cell
Material is carried in a membranous sac called a vesicle
Vesicle migrates to plasma membrane
Vesicle combines with plasma membrane
Material is emptied to the outside
Refer to Pathway 1 in Figure 3.6
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11. Lysosome fuses with ingested substances. Membrane
Figure 3.6 Role of the Golgi apparatus in packaging the products of the rough ER.
Rough ER
Cisterns
Proteins in cisterns
Lysosome fuses with ingested substances.
Membrane
Transport vesicle
Golgi vesicle containing digestive enzymes becomes a lysosome.
Pathway 3
Pathway 2
Golgi vesicle containing membrane components fuses with the plasma membrane and is incorporated into it.
Golgi apparatus
Secretory vesicles
Pathway 1
Proteins
Golgi vesicle containing proteins to be secreted becomes a secretory vesicle.
Plasma membrane
Secretion by exocytosis
Extracellular fluid

12. Active Processes Vesicular transport (continued)
Exocytosis docking process
Transmembrane proteins on the vesicles are called v-SNAREs (v for vesicle)
Plasma membrane proteins are called t-SNAREs (t for target)
v-SNAREs recognize and bind t-SNAREs
Membranes corkscrew and fuse together
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13. Plasma membrane SNARE (t-SNARE)
Figure 3.12a Exocytosis.
Extracellular fluid
Plasma membrane SNARE (t-SNARE) 1
The membrane- bound vesicle migrates to the plasma membrane.
Vesicle SNARE (v-SNARE)
Molecule to be secreted
Secretory vesicle
Cytoplasm
Fusion pore formed
There, v-SNAREs bind with t-SNAREs, the vesicle and plasma membrane fuse, and a pore opens up. 2
Fused SNAREs
Vesicle contents are released to the cell exterior. 3
(a) The process of exocytosis

14. Figure 3.12b Exocytosis.
(b) Electron micrograph of a secretory vesicle in exocytosis (190,000×)

15. Active Processes Vesicular transport (continued) Endocytosis
Extracellular substances are engulfed by being enclosed in a membranous vescicle
Vesicle typically fuses with a lysosome
Contents are digested by lysosomal enzymes
In some cases, the vesicle is released by exocytosis on the opposite side of the cell
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16. Figure 3.13a Events and types of endocytosis.
Slide 1
Extracellular fluid
Cytosol
Plasma membrane
Vesicle
Lysosome 1
Vesicle fusing with lysosome for digestion
Release of contents to cytosol 2
Transport to plasma membrane and exocytosis of vesicle contents
Detached vesicle
Ingested substance
Membranes and receptors (if present) recycled to plasma membrane 3
Pit
(a)

17. Figure 3.13a Events and types of endocytosis.
Slide 2
Extracellular fluid
Plasma membrane
Vesicle fusing with lysosome for digestion 1
(a)

18. Figure 3.13a Events and types of endocytosis.
Slide 3
Extracellular fluid
Cytosol
Plasma membrane
Vesicle
Lysosome 1
Vesicle fusing with lysosome for digestion
Release of contents to cytosol 2
Transport to plasma membrane and exocytosis of vesicle contents
Detached vesicle
(a)

19. Figure 3.13a Events and types of endocytosis.
Slide 4
Extracellular fluid
Cytosol
Plasma membrane
Vesicle
Lysosome 1
Vesicle fusing with lysosome for digestion
Release of contents to cytosol 2
Transport to plasma membrane and exocytosis of vesicle contents
Detached vesicle
Ingested substance
Membranes and receptors (if present) recycled to plasma membrane 3
Pit
(a)

20. Active Processes Vesicular transport (continued) Types of endocytosis
Phagocytosis—“cell eating”
Cell engulfs large particles such as bacteria or dead body cells
Pseudopods are cytoplasmic extensions that separate substances (such as bacteria or dead body cells) from external environment
Phagocytosis is a protective mechanism, not a means of getting nutrients
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21. Figure 3.13b Events and types of endocytosis.
Cytoplasm
Extracellular fluid
Bacterium or other particle
Pseudopod
(b)

22. Active Processes Vesicular transport (continued) Types of endocytosis
Pinocytosis—“cell drinking”
Cell “gulps” droplets of extracellular fluid containing dissolved proteins or fats
Plasma membrane forms a pit, and edges fuse around droplet of fluid
Routine activity for most cells, such as those involved in absorption (small intestine)
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23. Figure 3.13a Events and types of endocytosis.
Extracellular fluid
Cytosol
Plasma membrane
Vesicle
Lysosome
Vesicle fusing with lysosome for digestion 1
Release of contents to cytosol 2
Transport to plasma membrane and exocytosis of vesicle contents
Detached vesicle
Ingested substance 3
Membranes and receptors (if present) recycled to plasma membrane
Pit
(a)

24. Active Processes Vesicular transport (continued) Types of endocytosis
Receptor-mediated endocytosis
Method for taking up specific target molecules
Receptor proteins on the membrane surface bind only certain substances
Highly selective process of taking in substances such as enzymes, some hormones, cholesterol, and iron
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25. Active Processes Vesicular transport (continued) Types of endocytosis
Receptor-mediated endocytosis
Both the receptors and target molecules are in a vesicle
Contents of the vesicles are dealt with in one of the ways shown in the next figure
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26. Figure 3.13a Events and types of endocytosis.
Extracellular fluid
Cytosol
Plasma membrane
Vesicle
Lysosome
Vesicle fusing with lysosome for digestion 1
Release of contents to cytosol 2
Transport to plasma membrane and exocytosis of vesicle contents
Detached vesicle
Ingested substance 3
Membranes and receptors (if present) recycled to plasma membrane
Pit
(a)

27. Figure 3.13c Events and types of endocytosis.
Membrane receptor
(c)