Self assembly ​of a Lipid Bilayer

• Watch the self assembly of a lipid bilayer video cl​ip.

  • ​Note the constant collisions of blue,polar water molecules

  • ​The green portion of the phospholipid cannot attract to water

  • ​the red portion of the phospholipid remains towards the water as the slightly negative charge of the phosphate attracts to the slightly positive charge of water.

​Vesicles are Lipid Bilayers in a circle that will Fuse together in water

• ​As you watch the video, notice

  • ​The blue water molecules in constant motion

  • ​Pay attention to the small pink particles..they bounce around; can move through membrane but can't seem to stay anywhere there is water...what type of molecule is this pink particle ..polar or nonpolar

  • ​the many separate vesicles start to fuse with each other

  • ​the green portion of the phospholipid must be the polar end. Why???

​Vesicles can self assemble and trap polar molecules inside of it.

• ​Note the red polar molecules can be trapped as a lipid bilayer self assembles around it.

• ​If the red polar molecules represent polar proteins, this vesicle filled with these polar proteins can fuse with other cell membranes very easily to either form a larger vesicle or fuse with the outer cell membrane to dump the proteins outside of the cell.

The Endomembrane System and Vesicle Transport

• All cells are protein producing factories.

• Problem: Proteins are polar molecules that can't pass through the membrane.

  • ​Example, in a complex organism like a human, the pancreas cells produce tons of insulin that have to be transported out of the cell into the blood stream. How do we do this if insulin is polar????

• ​Eukaryotic cells have a system of wrapping the proteins in fatty vesicles that can fuse with the cell's membrane.