One possible molecule that can be added to a membrane to make it easier for membrane proteins to move about is cholesterol. Cholesterol helps to maintain the fluidity of the membrane by preventing the fatty acid tails of the phospholipids from packing too tightly together. This allows membrane proteins to move laterally within the membrane, facilitating their interactions with other molecules and their proper functioning. Other molecules, such as glycolipids and glycoproteins, can also affect the fluidity and movement of membrane proteins, but cholesterol is a major contributor to these properties.