Chemical Composition Of Plasma Membrane

C) Describe the chemical composition of the plasma membrane and relate it to membrane function. The plasma membrane is the outer limiting membrane of a cell that separates the body’s two major fluid components, the intercellular fluid that is within cells and the extracellular fluid outside of cells. It is very thin, about 7 to 10 nm, and is composed of a bilayer of lipid molecules with proteins dispersed in it. The phospholipid bilayer is composed of a portion that is hydrophilic, or attracted to water, and a portion that is hydrophobic, or water avoiding. The hydrophilic portion contains phosphorous and is the positively charged polar heads that appear on the inner and outer surfaces of the membrane. The negatively charged nonpolar tails

Diffusion describes the tendency of molecules to move from an area of high concentration to an area of low concentration. This is also known as moving down their concentration gradient. The particles in a solution are constantly in motion as a result of their kinetic energy. This causes collisions, which in turn causes the particles to ricochet off of one another and switch direction. Since the particles are in an area of high concentration, there is a greater likelihood of more collisions occurring, resulting in the particles being propelled in the opposite direction, or towards the area of low concentration, eventually leading to a sense of equilibrium of the particles on each side of the gradient. This is the diffusion of the particles. The greater the difference in concentration, the faster diffusion will occur because there are more chances of collision, thus, more chances for the particles to diffuse down their concentration gradient. It is also worth noting that the speed of diffusion is greatly influenced by particle size and temperature. Simple diffusion is unassisted and it does not require energy. This is when nonpolar and lipid soluble substances diffuse directly through the phospholipid bilayer without any help. Examples of substances that pass through the lipid bilayer with ease include oxygen and carbon dioxide. Some molecules are unable to pass through the lipid bilayer through simple diffusion, so they must be assisted to gain access into the cell. This is done through a process known as facilitated diffusion. The substance being transported must either bind to a carrier protein, a membrane integral protein, to be carried across the membrane, or it moved through a water filled protein channel. These processes are known as carrier-mediated facilitated diffusion and channel-mediated facilitated diffusion. Lastly, osmosis is the diffusion of a solvent, such as water, through a selectively