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Study Guide

Chapter all: Membrane Transport of Small Molecules and the Electrical Properties of Membranes

12 pages183 viewsFall 2016

Department
Biology
Course Code
BIO120H1
Professor
all

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Membrane Transport of Small Molecules and the Electrical
Properties of Membranes
PRINCIPLES OF MEMBRANE TRANSPORT
- Lipid bilayers are naturally impermeable to ions. Small, hydrophobic or nonpolar
molecules can diffuse across a lipid bilayer.
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- Membrane transport proteins are specialized in transporting solutes across cell
membranes. Each protein often transports only a specific molecular species or a class
of molecules (such as ions, sugars, or amino acids). Transporters and channels are
the two major classes of membrane transport proteins.
- Transporters (also called carriers or permeases) bind the solute to be transported and
undergo conformational changes to transfer the solute across the membrane.
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- Channels interact weakly with the solute and form continuous pores that extend across
the lipid bilayer, which allow specific solutes to pass through them. Transport through
channels occurs at a much faster rate than transport mediated by transporters.
- Passive transport does not require energy and occurs in the direction of a
concentration gradient.
- Membrane potential is de difference between electrical potential on the two sides of
the membrane.
- The concentration gradient and the electrical gradient combine to form a net driving
force, the electrochemical gradient.
- Active transport occurs against an electrochemical gradient, thus requiring an energy
source such as ATP hydrolysis.
TRANSPORTERS AND ACTIVE MEMBRANE TRANSPORT
- Active transport can be done in three ways: coupled transport, ATP-driven and light or
redox-driven.
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