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
- 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)
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)
click to edit
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
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