Cell membrane 🔬

Membrane basics

plasma membrane encloses the cell.

inside the cell most organelles are defined by their membrane. same function - separate specialized environments.

bilayer of lipids, with embedded proteins which define the organelle and most of the work.

  • a very thin layer
  • the film of lipid and embedded protein makes it impenetrable to most water-soluble molecules (including hormones & drugs)
  • makes them fluid and dynamic & fluid
  • most of the molecules constantly move in the plane of the membrane

Gonna look at the lipid bilayer in more detail.

  • the bilayer structure is due to the physical properties of the lipid molecules.
  • they assemble spontaneously

The lipid bilayer

shapes shpherical micelles or bilayer double layer sheets Cell membrane 1

  • the hydrophobic forces provides a self sealing property. - if there is a tear, the lipids of membrane will spontaneously fold to eliminate the edges
  • bc edges means hydrophobic parts exposed (we don't want that)
    cell membrane 2

Amphiphilic = has hydrophobic (non-polar) and hydrophilic (polar) parts.


  • we often see that the hydrophobic tails of lipids get berried while the hydrophilic parts are exposed.
  • this results in different shapes
  • different phospholipids can have different shapes: cylinders/ cones
  • essential for formation of membrane
    • seeing as they allow proteins to be embedded.
    • And for processes such as membrane fusion and fission (needs curvature)
      cell membrane 3

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the polar head group contains a PO4 group

the 2 hydrophobic tails are fatty acids

-once tail has 1/more cis-double bonds (unsaturated) and appears bent

  • other tail does not have double bonds = saturated

tails between 14 - 24 carbon atoms in length

different lengths and saturation = different membrane fluidity

CM4

list of things affecting fluidity of membrane

  • fatty acid composition - length & saturation
  • Sterol - content
  • temp - environment

changes in fluidity also called phase transition

Hydrocarbon chain is short & has double bonds (unsaturated) = fluid at low temp

CM5