The other end contains a nitrogen containing group. The phosphate group is charged and the nitrogen containing group picks up a hydrogen ion and becomes positively charged. The charged end of the molecule is soluble in water and the fatty acid end of the molecule is nonpolar and insoluble in water. This property makes these molecules good as constituents of cell membranes. These are lipids because their properties such as solubility are similar to those of other classes such as fats.
All steroids consist of four interlocking rings.
Differ only in nature of side groups. Overhead is cholesterol. Proteins Proteins are the most fundamental units of the cell. Many different proteins exist but all are composed of the same building units. All proteins contain carbon, hydrogen, nitrogen and oxygen and some contain sulfur.