As part of your drawing, describe the jobs of the proteins you were asked to include in your membrane drawing. Transport and receptor proteins are inserted into the membrane. Transport proteins allow for the passage of compounds into and out of the cell, while receptor proteins serve as communication devices for the cell. Passive transport proteins transport small molecules or ions that do not require energy to enter the cell, but can not pass through the phospholipid bilayer. Passive transport of water, oxygen, and CO2 across the cell membrane, depends on the concentrations of these materials on either side of the membrane.
Movement is from a higher concentration to a lower concentration.
Passive movement may be through the phospholipid bilayer for fat-soluble molecules or through protein molecules for others. Active transport proteins facilitate the movement of large molecules or charged ions across membranes against a concentration gradient - from an area of low concentration to an area of high concentration. Active transport of larger molecules, like glucose or charged ions moving against a concentration gradient requires the expenditure of energy in the form of ATP in conjunction with special membrane proteins. Hormone receptor proteins have specific shapes and chemical properites that allow them to bind to specific types of hormone molecules in the environment of the cell. Receptor proteins in the outer cell membrane interact with molecules outside the cell.