First, it should be noted that proteins are fundamentally different from carbohydrates and lipids. Lipids are made up of approximately 75% to 85% carbon, and carbohydrates contain about 50% oxygen and less than 5% nitrogen. However, the proteins (and peptides) possess between 15% and 25% nitrogen and about an equal amount of oxygen. Other elements include sulfur atoms and are specically found in the amino acids cysteine and methionine. Proteins and peptides differ in their size: peptides are considered as small proteins, having molecular weights of less than 10,000 daltons. But all proteins and peptides are constructed from amino acids.