BIO1011 Lecture Notes - Lecture 6: Membrane Transport, Passive Transport, Membrane Transport Protein
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PRINCIPLES OF MEMBRANE TRANSPORT
1. Lipid bilayers are impermeable to solutes and ions
2. Membrane transport proteins fall into two classes: transporters and channels
3. Solutes cross membranes by passive or active transport
1. Lipid Bilayers Are Impermeable to Solutes and Ions
•The smaller the molecule and, more importantly, the less strongly it associates with
water, the more rapidly the molecule diffuses across the bilayer.
Can move easy through osmosis
Will move across fairly well
These will not move across the
membrane because these cannot interact
with the hydrophilic and hydrophobic area.
2. Membrane Transport Proteins Fall into Two Classes: Transporters and Channels
•A transporter alternates between two formations, so that the solute-binding site is
sequentially accessible on both sides of the bilayer
•There is speciﬁcity with the binding, so only certain solute will use this carrier protein.
•In contrast, a channel protein forms a water-ﬁlled pore across the bilayer through which
speciﬁc solutes can diffuse.
•The size and charge of the ion is speciﬁc for a particular channel.
3. Solutes Cross Membranes by Passive or Active Transport
•Passive transport - requires no energy and is the movement of molecules along the
•This can use the channel or transporter
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