Structure of Membranes

Cell membranes are composed of many phospholipids. There are two parts to a phospholipid; the head and the tail. The head is hydrophilic; meaning that it loves water. The tail is the exact opposite, it is hydrophobic. These opposing parts of the phospholipid contributes heavily to the structure of the cell membrane.

Several phospholipids make up the cell membrane. A hydrophobic phospholipid consists of 16-18 carbon, hydro carbon backbone. They also contains small amounts on oxygen.

Fatty acids are generally 16-22 carbons long. There are two types of fatty acids; saturated and unsaturated. Saturated fatty acids have no carbon-carbon double bonds saturated with hydrogen. Unsaturated fatty acids have one to three double bonds along the backbone carbon chain - "kinks" in the carbon chain. Fats are storage for energy and insulating molecules. They contain twice as much energy as carbohydrates. Unsaturated fat has one unsaturated fatty acids. Saturated fats have none. 

The bending of the tail is a "kink".

Phospholipids contain only two fatty acids attached to a glycerol head. The third alcohol of the glycerol forms an ester bond. As a triprotic acid, the phosphate head has the potential to form ester links with a variety of other types of molecules like carbohydrates or amino acids. 

Micelle Formation

Liposome Formation

Steroids are four fused carbon rings. They include many hormones as well as cholesterol. Cholesterol is a major player is cell membranes. Steroids restrict the movement in fatty acids tails. 

The extracellular surface of the cell membrane is made of carbohydrates attached to lipids and proteins.
The proteins in the membrane enable the membrane to carry out normal activities. Proteins on the extracellular domain surface generally involve in cell-cell signaling and interactions. Domains inside the membrane move molecules across the membrane.

Below is a Fluid Mosiac Model I drew with a peer. It shows, further, how membranes are structured.

Diffusion and Osmosis

We also performed a lab to see how strong the membrane really is. We took a glucose/starch solution and put it into a rectangular, thin baggy. We put iodine water into a cup and placed the glucose/starch baggy into it. We tested each solution separately before placing the baggy into the cup. Of coarse, the glucose/starch solution came out positive for glucose. The iodine/water solution came out negative for glucose. We let the baggy sit in the cup for a couple days before coming back and testing each solution for glucose again. Both the starch/glucose and the iodine/water came out very positive for glucose. The starch glucose had also turned colors from a foggy white, to a dark dark blue color. Also, the iodine water turned a lighter color. Because the glucose/starch solution turned that blue color, this signifies that the polysaccharide (starch) is being affected by the iodine. This means that both the iodine solution as well as the glucose/starch solution are being affected by one another; they are mixing together in the cup as well as in the rectangular baggy. This part of the lab is a great example of diffusion. Diffusion is better known as migration; or an intermingling of molecules.
In the second part of the lab, we are mainly looking at osmosis. In four cups, all filled halfway with water, we placed four rectangular shaped baggies filled with different substances. In cup one; we had a baggy of corn syrup/water mix. In cup two; we had a baggy of sodium acetate/water mix. In cup three; we had a baggy of crushed antacid tablet/water mix. In cup four; we had a baggy of sodium bicarbonate/water mix. Initially, me and my peer weighed the baggies before they were placed in the cups filled halfway with water. The antacid baggy weighed 13.43g, the sodium acetate baggy weighed 13.74g, the corn syrup baggy weighed 11.93g, and the sodium bicarbonate baggy weighed 11.66g. An hour later, we came back to weigh them again to see if any water was coming in yet, and indeed there was. An hour later the antacid baggy weighed 14.74g, the sodium acetate baggy weighed 23.09g, the corn syrup baggy weighed 15.88g, and the sodium bicarbonate baggy weighed 12.09g. There was a dramatic change, especially in the sodium acetate baggy(even in appearance, it was very noticeable). The water had moved into the baggy very quickly as I had predicted because of how small the water molecules are. By the next day, the baggies had evened out, showing us that osmosis had, indeed, taken place. Below is a graph showing the changes that the baggies underwent.