Cell biology/Membrane Structure: Lipids

Here is the link to the ITunes U Lecture from Berkeley. Membrane Structure: Lipids

Textbook Recommended by Professor: Molecular Biology of the Cell, Alberts et. al.

How do we visualize a cell membrane?

How Can We Isolate a Membrane?

  1. This process involves taking tissue or cells and rupturing their cell membranes using a technique called vigorous homogenization (very similar to using a mortar and pestle). This produces pieces of membrane and organelles called lysate.
  2. Centrifuge to separate pieces which will settle at different rates: Nucleus first, Endoplasmic Reticulum last. Using centrifuging to separate cell parts is called differential centrifugation and it separates lysate according to mass.
  3. A sucrose gradient, a gradient is created using an increasing concentration of sucrose as you move down the centrifuge tube. When the lysate is added to this tube and centrifuged, the lysate travels to the point where it's density is matched by the surrounding sucrose.

Membrane Properties

Selective Permeability

The phospholipid membrane itself does not allow polar or charged species to flow through it. There are channels, permeases, that allow charged and polar substances entry and exit from the cell.

Oxidative Phosphorylation in Mitochondria

Mechanically Deformable

Membranes can be deformed because they are fluid. Hence fluid-mosaic model. This property comes from the phospholipid bilayer. A membrane is pictured as a mosaic because it has various protein molecules embedded in the phospholipid bilayer .

Communication

Membranes serve in cell-cell communication and signal transduction in the nervous and muscular systems.

Phospholipid bilayer

The image is wrong and needs correction. too many bonds are on carbon atoms and oxygen atoms.

The head group points towards the outside of the membrane while the tail group is hydrophobic and points inward. There are some very common fatty acid side chains (R groups: R1 and R2) including:

  1. palmitate, 16 carbon saturated fatty acid chain.
  2. oleate, an 18 carbon unsaturated fatty acid chain with a single double bond.
  3. sterate, an 18 carbon saturated fatty acid chain.

Saturated bonds are very flexible but double bonds create kinks and limit flexibility.

Phospholipids have a amphipathic property or nonpolar and polar properties.


For more information check out: The Wikipedia Page

Please feel free to add details or make changes where necessary. Contact me via email if you need help. Thanks, April

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