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Lipid Bilayer

Def: this has been firmly established as the universal basis of membrane structure, and its properties are responsible for th general properties of all cell membranes.

Info: This makes up not only the plasma membrane but all membranes are made up of lipid bilayers. It behaves as a two demensional fluid, which makes it very flexible.

The flexibility and fluidity of the lipid bilayer depends on it's phospholipid composition and the nature of the hyrdocarbon tails. The closer the tails, the less fluid the lipid bilayer will be
- A short tail chain increases fluidity
-lipids with more unsaturated tails are more fluid then lipids with a higher number of saturated tails (because unsaturated tails have kinks in them from double bonds and it makes it harder for the tails to pack close together, and packing close together makes the bilayer rigid and grumpy).


  • a hydrophilic (water lovin) head and one or two hydrophobic (water hatin) tails.

Lipid Asymmetry

cell membranes are generally asymmetrical. (the inside is much different then the outside)

info: this is established and maintained as the membrane grows.
New phospholipids are manufactured by enzymes that are bound to the part of the E.R that faces the cytosol.
-these enzymes deposit all of the newly made phospholipids into the cytosolic half of the bilayer.
-so that the cell membrane can grow evenly, half of the newly made phospholipids must be transported to the opposite monolayer. (this is done by flippases that catalyze this transfer)


def: a synthetic lipid bilayer in the form of a closed sphere. Used by sceintists in experiments to see how the lipid bilayer works. it forms if pure phospolipids are added to water.

Lagging Strand (chapter 6)

def: One of the two newly made strands of DNA found at a replication fork. The lagging strand is made on discontinuous lengths that are later joined covalently.

Leading Strand (chapter 6)

def: One of the two newly made strands of DNA found at a replication fork. The leading strand is made by continuous synthesis in the 5'-to-3' direction.

Lysosome (chapter 15)

def: Intracellular membrane-enclosed organelle containing digestive enzymes, typically those most active at the acid pH found in those organelles.

Local Mediator (chapter 17)

def: Secreted signal molecule that acts at a short range on adjacent cells.

Lamellipodium (chapter 16)

def: Dynamic sheet-like extension on the surface of an animal cell, especially one migrating over a surface.

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