This week was about the cell membrane. The structure of the cell membrane is a fluid mosaic model composed of a phospholipid bilayer. It is a boundary to the cell, transports materials in and out of the cell, and communicates between the cell and it’s environment.
The phospholipids have a hydrophilic head and a hydrophobic tail which allows them to organize into a bilayer automatically when submerged in water. They are fluid and are constantly moving. The bilayer makes a selectively permeable membrane that only allows small, non-polar molecules through directly.
Other molecules can enter into the cell but require help from tranfer proteins which ask as gates or bridges through the cell membrane. Integral proteins go all the way through the cell membrane while peripheral proteins only penetrate one layer. Integral proteins have many functions including transport, enzymatic activity, signal transduction, cell to cell recognition, intercellular joining, attachment to the cytoskeleton and extra cellular matrix.
Cholesterol acts as a temperature buffer to maintain the buffer of the cell wall. It is a steroid lipid that helps keep the membrane fluid.
We also talked about transport, including active transport and passive transport. Passive transport is diffusion where items of a high concentration spread out to a low concentration because of the law of increasing entropy. This type of transport takes no energy to happen. Active transport, on the other hand, does require energy because it requires items to go from a low to high concentration. Ex. waterfall. Both types of transport sometimes require transport proteins in order for molecules to get through the cell wall.
Sara Irvin- AP Biology 