Cell Biology: Describe how the lipid bilayer is produced and assembled and identify and discuss the factors that impact fluidity of the lipid bilayer

How is the membrane assembled?

1. Phospholipids are built by the cytosolic enzymes on the ER and deposited in the ER lumen. 2. The phospholipids are then added to the cytosolic half of the bilayer in the lumen and distributed to the body. 3. Scramblase then comes in and transfers random phospholipids from one monolayer to the other, redistributing to create a symmetrical bilayer where the heads are on the correct side depending on their jobs in cell signaling and recognition. 4. This is now the ER membrane. 5. Sometimes, the phospholipids will be sent to supply the Gogi and plasma membrane. In this case, the membrane is delivered by the ER. 6. Once it arrives, flippase catalyzes the transfer of specific phospholipids to the cytosolic monolayer creating an asymmetrical membrane.

How does fluidity impact permeability?

As fluidity decreases permeability will too.

Why is fluidity important?

It allows the membrane proteins to rapidly move in plane of the bilayer to interact with each other, it also allows for lipids and proteins to move from bilayer to other cell regions and enables membranes to fuse with one another. It is also very important for cell growth and reproduction.

What factors effect fluidity and how?

Tail lengths- shorter tails decrease hydrocarbon interactions increasing fluidity. Number of double bonds- the more unsaturated bonds cause more kinks so less packing will occur increasing fluidity. Cholesterol- cholesterol fills the gaps in the bilayer causing it to stiffen and reducing fluidity. However, in high temperatures, it will stabilize the layer by increasing fluidity.

What is fluidity?

The ease at which lipids/ proteins can move withing the plane of the membrane.

How is the lipid bilayer formed during self-repair?

The planar layer has hydrophobic tails that are exposed to water causing the amphipathic sheet to bend and seal to keep the tails from contacting the water. This also aids in self-healing of the membrane.