When hydrogen is bonded to an electronegative atom, it gains a slight positive charge and is weakly attracted to another electronegative atom. This weak attraction is a hydrogen bond. Acids donate hydrogen ions to solution, whereas bases lower the hydrogen ion concentration on a solution. The pH scale is a negative function of the logarithm of the hydrogen ion concentration. Bonds are broken by hydrolysis reactions.
Lipids are organic molecules that are insoluble in polar solvents such as water.
The rest of the molecule is hydrophobic. Proteins are composed of long chains of amino acids bound together by covalent peptide bonds. Each amino acid contains an amino group, a carboxyl group, and a functional group. Differences in the functional groups give each of the more than twenty different amino acids an individual identity. Proteins may be combined with carbohydrates, lipids, or other molecules.