Lipid Bilayer – Biological Membranes

by Kevin Ahern, PhD

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    00:01 Now the lipid bilayer as I said, defines the boundary of cells and organelles. It is comprised of two layers of amphiphilic molecules. These layers of amphiphilic molecules provide a significant barrier to most substances. Now there are some exceptions to that barrier.

    00:18 Lipid bilayers are relatively permeable to water, molecular oxygen, carbon dioxide and carbon monoxide. Now this turns out to be pretty important, at least for the oxygen and carbon dioxide parts, because oxygen is needed for respiratory functions by aerobic cells and carbon dioxide is expelled or given away, given off as a result of oxidation and cells need to get rid of that. So having these being freely transportable across membranes is very good. Carbon monoxide can be hazardous to cells so that's kind of a lose function on that, and water is interesting in the sense that water can cause problems because of its permeability across cells as we shall see.

    01:04 Now this depicts a lipid bilayer of a cell in the lower right. For the purposes of this illustration, I've made the outside of the cell be the top and the inside of the cell be the bottom. The lipid bilayer as its name suggests, has two layers. A top layer that is comprised of amphiphilic molecules like I've discussed in other modules here. And the molecules are arranged so the polar ends of them are pointed outwards in areas that interact with water. So outside of the cell there's water, inside of the cell there's water, but within the lipid bilayer we have a hydrophobic interior where the long chains of fatty acids that don't like water can associate with each other. Now interestingly this combination of hydrophilic substances on the outside and the hydrophobic on the inside is what provides a significant barrier to substances. This can be good if the substances, of course, are toxic to the cell but it can also be bad or difficult if the substances are nutrients that the cell needs. Fortunately cells have ways of dealing that as we shall see via the use of transport systems.

    About the Lecture

    The lecture Lipid Bilayer – Biological Membranes by Kevin Ahern, PhD is from the course Biochemistry: Basics.

    Included Quiz Questions

    1. They are comprised of a lipid bilayer.
    2. They are found only in the cell walls of eukaryotic cells.
    3. They are impermeable to all substances.
    4. They are noted for their rigidity.
    5. They have a hydrophilic interior and hydrophobic exterior.

    Author of lecture Lipid Bilayer – Biological Membranes

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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