1. Active Transport: Two Types
Primary AT
-Energy directly from ATP hydrolysis
Secondary AT
Energy indirectly from ionic gradients created by primary AT
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2. Primary Active Transport
Hydrolysis of ATP causes shape change in transport protein that "pumps" ions across PM
E.g., Ca++, H+, Na+-K+ pumps
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3. Primary Active Transport
Sodium-potassium pump
Carrier (pump) called Na+-K+ ATPase
Involved in primary / secondary AT
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4. Figure Primary active transport is the process in which solutes are moved across cell membranes against electrochemical gradients using energy supplied directly by ATP.
Slide 2
Extracellular fluid
Na+
Na+–K+ pump K+
ATP-binding site
Cytoplasm
1 Three cytoplasmic Na+ bind to pump
protein.
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5. Figure Primary active transport is the process in which solutes are moved across cell membranes against electrochemical gradients using energy supplied directly by ATP.
Slide 3
Extracellular fluid
Na+
Na+–K+ pump K+
Na+ bound
ATP-binding site
Cytoplasm
1 Three cytoplasmic Na+ bind to pump
protein. P
2 Na+ binding promotes hydrolysis of ATP.
The energy released during this reaction
phosphorylates the pump.
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6. Figure Primary active transport is the process in which solutes are moved across cell membranes against electrochemical gradients using energy supplied directly by ATP.
Slide 4
Extracellular fluid
Na+
Na+–K+ pump K+
Na+ bound
ATP-binding site
Cytoplasm
1 Three cytoplasmic Na+ bind to pump
protein. P
2 Na+ binding promotes hydrolysis of ATP.
The energy released during this reaction
phosphorylates the pump.
Na+ released P
3 Phosphorylation causes the pump to
change shape, expelling Na+ to the outside.
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7. 4 Two extracellular K+ bind to pump.
Figure Primary active transport is the process in which solutes are moved across cell membranes against electrochemical gradients using energy supplied directly by ATP.
Slide 5
Extracellular fluid
Na+
Na+–K+ pump K+
Na+ bound
ATP-binding site
Cytoplasm
1 Three cytoplasmic Na+ bind to pump
protein. P
2 Na+ binding promotes hydrolysis of ATP.
The energy released during this reaction
phosphorylates the pump.
Na+ released P K+
3 Phosphorylation causes the pump to
change shape, expelling Na+ to the outside. P
4 Two extracellular K+ bind to pump.
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8. 4 Two extracellular K+ bind to pump.
Figure Primary active transport is the process in which solutes are moved across cell membranes against electrochemical gradients using energy supplied directly by ATP.
Slide 6
Extracellular fluid
Na+
Na+–K+ pump K+
Na+ bound
ATP-binding site
Cytoplasm
1 Three cytoplasmic Na+ bind to pump
protein. P
2 Na+ binding promotes hydrolysis of ATP.
The energy released during this reaction
phosphorylates the pump.
Na+ released
K+ bound P Pi K+
5 K+ binding triggers release of the
phosphate. The dephosphorylated pump
resumes its original conformation.
3 Phosphorylation causes the pump to
change shape, expelling Na+ to the outside. P
4 Two extracellular K+ bind to pump.
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9. 4 Two extracellular K+ bind to pump.
Figure Primary active transport is the process in which solutes are moved across cell membranes against electrochemical gradients using energy supplied directly by ATP.
Slide 7
Extracellular fluid
Na+
Na+–K+ pump K+
Na+ bound
ATP-binding site
Cytoplasm
1 Three cytoplasmic Na+ bind to pump
protein. P
K+ released
6 Pump protein binds ATP; releases K+ to
the inside, and Na+ sites are ready to bind
Na+ again. The cycle repeats.
2 Na+ binding promotes hydrolysis of ATP.
The energy released during this reaction
phosphorylates the pump.
Na+ released
K+ bound P Pi K+
5 K+ binding triggers release of the
phosphate. The dephosphorylated pump
resumes its original conformation.
3 Phosphorylation causes the pump to
change shape, expelling Na+ to the outside. P
4 Two extracellular K+ bind to pump.
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10. Secondary Active Transport
Depends on ion gradient created by primary AT
Cotransport—transports more than one substance at a time
Symport system:Transported same direction
Antiport system: Transported opposite direction
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11. Primary active transport
Figure Secondary active transport is driven by the concentration gradient created by primary active transport.
Slide 2
Extracellular fluid
Na+-K+
pump
Cytoplasm
Primary active transport
The ATP-driven Na+-K+ pump stores energy by creating a steep concentration gradient for Na+ entry into the cell. 1
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12. Primary active transport
Figure Secondary active transport is driven by the concentration gradient created by primary active transport.
Slide 3
Extracellular fluid
Glucose
Na+-glucose
symport transporter
releases glucose
into the cytoplasm
Na+-glucose
symport
transporter
loads glucose
from extracellular
fluid
Na+-K+
pump
Cytoplasm
Primary active transport
The ATP-driven Na+-K+ pump stores energy by creating a steep concentration gradient for Na+ entry into the cell. 1
Secondary active transport
As Na+ diffuses back across the membrane
through a membrane cotransporter protein, it
drives glucose against its concentration gradient
into the cell. 2
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13. Vesicular Transport Functions: Exocytosis—out of cell
Endocytosis—into cell
Phagocytosis, pinocytosis, receptor-mediated endocytosis
Transcytosis—into, across, and out of cell
Vesicular trafficking—from one area to another
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14. Endocytosis and Transcytosis
Formation of protein-coated vesicles
Often receptor mediated, very selective
Some pathogens hijack for transport into cell
Once vesicle is inside cell it may
Fuse with lysosome
Undergo transcytosis
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15. Figure 3.12 Events of endocytosis mediated by protein-coated pits.
Slide 2
Coated pit ingests substance. 1
Extracellular fluid
Plasma
membrane
Protein coat
(typically
clathrin)
Cytoplasm
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16. Figure 3.12 Events of endocytosis mediated by protein-coated pits.
Slide 3
Coated pit ingests substance. 1
Extracellular fluid
Plasma
membrane
Protein coat
(typically
clathrin)
Cytoplasm
Protein-coated vesicle deta-
ches. 2
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17. Figure 3.12 Events of endocytosis mediated by protein-coated pits.
Slide 4
Coated pit ingests substance. 1
Extracellular fluid
Plasma
membrane
Protein coat
(typically
clathrin)
Cytoplasm
Protein-coated vesicle deta-
ches. 2
Coat proteins are recycled to plasma membrane. 3
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18. Figure 3.12 Events of endocytosis mediated by protein-coated pits.
Slide 5
Coated pit ingests substance. 1
Extracellular fluid
Plasma
membrane
Protein coat
(typically
clathrin)
Cytoplasm
Protein-coated vesicle deta-
ches. 2
Coat proteins are recycled to plasma membrane. 3
Uncoated endocytic
vesicle
Endosome
Uncoated vesicle fuses with a sorting vesicle called an endosome. 4
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19. Figure 3.12 Events of endocytosis mediated by protein-coated pits.
Slide 6
Coated pit ingests substance. 1
Extracellular fluid
Plasma
membrane
Protein coat
(typically
clathrin)
Cytoplasm
Protein-coated vesicle deta-
ches. 2
Coat proteins are recycled to plasma membrane. 3
Transport
vesicle
Uncoated endocytic
vesicle
Endosome
Uncoated vesicle fuses with a sorting vesicle called an endosome. 4
Transport
vesicle containing 5
membrane compone
-nts moves to the plasma
membrane for recycling.
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20. Figure 3.12 Events of endocytosis mediated by protein-coated pits.
Slide 7
Coated pit ingests substance. 1
Extracellular fluid
Plasma
membrane
Protein coat
(typically
clathrin)
Cytoplasm
Protein-coated vesicle deta-
ches. 2
Coat proteins are recycled to plasma membrane. 3
Transport
vesicle
Uncoated endocytic
vesicle
Endosome
Uncoated vesicle fuses with a sorting vesicle called an endosome. 4
Transport
vesicle containing 5
membrane compone
-nts moves to the plasma
membrane for recycling.
Lysosome
Fused vesicle may (a) fuse with lysosome for digestion of its contents, or (b) deliver its contents to the plasma membrane on the opposite side of the cell (transcytosis). 6
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21. Figure 3.13a Comparison of three types of endocytosis.
Phagocytosis
The cell engulfs a large particle
by forming projecting pseudopods ("false feet") around it and enclosing it within a membrane sac called a phagosome. The phagosome is combined with a lysosome. Undigested contents remain in
the vesicle (now called a residual body) or are ejected by exocytosis. Vesicle may or may not be protein coated but has receptors capable of binding to microorganisms or solid particles.
Receptors
Phagosome
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22. Figure 3.13b Comparison of three types of endocytosis.
Pinocytosis
The cell "gulps" a drop of extracellular fluid containing solutes into tiny vesicles. No receptors are used, so the process is nonspecific. Most vesicles are protein-coated.
Vesicle
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23. Receptor-mediated endocytosis
Allows specific endocytosis and transcytosis
Clathrin-coated pits provide main route for endocytosis and transcytosis
Uptake of enzymes, LDLs, iron, insulin, and, unfortunately, viruses, diphtheria, and cholera toxins
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24. Figure 3.13c Comparison of three types of endocytosis.
Receptor-mediated endocytosis
Extracellular substances bind to specific receptor proteins, enabling the cell to ingest and concentrate specific substances (ligands) in protein-coated vesicles. Ligands may simply be released inside the cell, or combined with a lysosome to digest contents. Receptors are recycled to the plasma membrane in vesicles.
Vesicle
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25. © 2013 Pearson Education, Inc.

26. Usually activated by cell-surface signal or change in membrane voltage
Exocytosis
Usually activated by cell-surface signal or change in membrane voltage
Substance enclosed in secretory vesicle
Functions
Hormone secretion, neurotransmitter release, mucus secretion, ejection of wastes
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27. The process of exocytosis
Figure Exocytosis.
Slide 2
The process of exocytosis
Plasma membrane
SNARE (t-SNARE)
Extracellular
fluid
Secretory
vesicle
Vesicle
SNARE
(v-SNARE)
1 The membrane-
bound vesicle
migrates to the
plasma membrane.
Molecule to
be secreted
Cytoplasm
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28. The process of exocytosis
Figure Exocytosis.
Slide 3
The process of exocytosis
Plasma membrane
SNARE (t-SNARE)
Extracellular
fluid
Secretory
vesicle
Vesicle
SNARE
(v-SNARE)
1 The membrane-
bound vesicle
migrates to the
plasma membrane.
Molecule to
be secreted
Cytoplasm
2 There, proteins at the vesicle surface (v-SNAREs) bind with t-SNAREs (plasma membrane proteins).
Fused
v- and
t-SNAREs
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29. Fusion pore formed Cytoplasm
Figure Exocytosis.
Slide 4
The process of exocytosis
Plasma membrane
SNARE (t-SNARE)
Extracellular
fluid
Fusion pore formed
3 The vesicle
and plasma
membrane
fuse and a pore
opens up.
Secretory
vesicle
Vesicle
SNARE
(v-SNARE)
1 The membrane-
bound vesicle
migrates to the
plasma membrane.
Molecule to
be secreted
Cytoplasm
2 There, proteins at the vesicle surface (v-SNAREs) bind with t-SNAREs (plasma membrane proteins).
Fused
v- and
t-SNAREs
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30. Fusion pore formed Cytoplasm
Figure Exocytosis.
Slide 5
The process of exocytosis
Plasma membrane
SNARE (t-SNARE)
Extracellular
fluid
Fusion pore formed
3 The vesicle
and plasma
membrane
fuse and a pore
opens up.
Secretory
vesicle
Vesicle
SNARE
(v-SNARE)
1 The membrane-
bound vesicle
migrates to the
plasma membrane.
Molecule to
be secreted
Cytoplasm
4 Vesicle
contents are
released to the
cell exterior.
2 There, proteins at the vesicle surface (v-SNAREs) bind with t-SNAREs (plasma membrane proteins).
Fused
v- and
t-SNAREs
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31. Photomicrograph of a secretory vesicle releasing its contents
Figure 3.14b Exocytosis.
Photomicrograph
of a secretory
vesicle releasing
its contents
by exocytosis
(100,000x)
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32. Table 3.2 Active Membrane Transport Processes (1 of 2)
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33. Table 3.2 Active Membrane Transport Processes (2 of 2)
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34. Generation of a Resting Membrane Potential
Resting membrane potential (RMP)
Produced by separation of oppositely charged particles (voltage) across PM in all cells
Cells described as polarized
Voltage (electrical potential energy) only at PM
Ranges from –50 to –100 mV in different cells
"–" indicates inside negative relative to outside
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35. Extracellular fluid + + + + + + + +
Figure The key role of K+ in generating the resting membrane potential.
Slide 2
1 K+ diffuse down their steep
concentration gradient (out of the cell)
via leakage channels. Loss of K+
results in a negative charge on the
inner plasma membrane face.
Extracellular fluid + + + + + + + + – – – – – – –
Potassium
leakage
channels –
Protein anion (unable to
follow K+ through the
membrane)
Cytoplasm
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36. Extracellular fluid + + + + + + + +
Figure The key role of K+ in generating the resting membrane potential.
Slide 3
1 K+ diffuse down their steep
concentration gradient (out of the cell)
via leakage channels. Loss of K+
results in a negative charge on the
inner plasma membrane face.
Extracellular fluid
2 K+ also move into the cell
because they are attracted to the
negative charge established on the
inner plasma membrane face. + + + + + + + + – – – – – – –
Potassium
leakage
channels –
Protein anion (unable to
follow K+ through the
membrane)
Cytoplasm
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37. Extracellular fluid + + + + + + + +
Figure The key role of K+ in generating the resting membrane potential.
Slide 4
1 K+ diffuse down their steep
concentration gradient (out of the cell)
via leakage channels. Loss of K+
results in a negative charge on the
inner plasma membrane face.
Extracellular fluid
2 K+ also move into the cell
because they are attracted to the
negative charge established on the
inner plasma membrane face. + + + + + + + + – – –
3 A negative membrane potential
(–90 mV) is established when the
movement of K+ out of the cell equals
K+ movement into the cell. At this
point, the concentration gradient
promoting K+ exit exactly opposes the
electrical gradient for K+ entry. – – – –
Potassium
leakage
channels –
Protein anion (unable to
follow K+ through the
membrane)
Cytoplasm
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38. Active Transport Maintains Electrochemical Gradients
Na+-K+ pump continuously ejects 3Na+ from cell and carries 2K+ in
Steady state maintained because rate of active transport equal to and depends on rate of Na+ diffusion into cell
Neuron and muscle cells "upset" RMP by opening gated Na+ and K+ channels
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39. http://highered. mcgraw-hill
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40. Roles of Cell Adhesion Molecules
Anchor to extracellular matrix or each other
Assist in movement of cells past one another
Attract WBCs to injured or infected areas
Transmit intracellular signals to direct cell migration, proliferation, and specialization
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