Active transport

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Chapter 5
Active Transport
You Must Know
• The role of active transport, including the
sodium potassium pump and cotransport, in
cells.
CONCEPT 5.4: Active Transport
• Active transport moves
substances against their
concentration gradients.
• Active transport requires
energy, usually in the
form of ATP.
• Active transport allows
cells to maintain
concentration gradients
that differ from their
surroundings
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• Sodium-potassium pump transports 3 sodium
ions out of the cell and two potassium ions
into the cell.
EXTRACELLULAR
FLUID
1
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CYTOPLASM
[Na] high
[K] low
[Na] low
[K] high
2
6
3
5
4
ADP
How Ion Pumps Maintain Membrane Potential
• Membrane potential is the voltage across a
membrane.
• Voltage is created by differences in the
distribution of positive and negative ions across a
membrane.
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• Two combined forces, collectively called the
electrochemical gradient, drive the diffusion of
ions across a membrane.
1. A chemical force (the
ion’s concentration
gradient).
2. An electrical force (the
effect of the membrane
potential on the ion’s
movement).
• An electrogenic pump is a transport protein that
generates voltage across a membrane.
• The sodium-potassium pump is the major
electrogenic pump of animal cells.
© 2014 Pearson Education, Inc.
Figure 5.16
The main electrogenic pump of plants, fungi, and
bacteria is a proton pump.
Electrogenic pumps help store energy that can be used
for cellular work.
EXTRACELLULAR
FLUID
Proton pump
CYTOPLASM
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Cotransport: Coupled Transport by a Membrane Protein
Proton pump
Sucrose-H
cotransporter
Diffusion of H
Sucrose
Sucrose
© 2014 Pearson Education, Inc.
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