Question 4
What is the building unit of a protein?
The right answer is the one marked above.
Amino acids. A protein is a complex molecule built by joining a great many of these simpler molecules together.
It is the same pattern all four biological molecules follow — a small unit repeated to build something large. Monosaccharides build carbohydrates, fatty acids and glycerol build lipids, and nucleotides build nucleic acids.