When amino acids join together, what do they form?

Amino acids are the building blocks of proteins. When two or more amino acids chemically bond through peptide bonds, they form polypeptides, which can then fold into specific three-dimensional structures to become functional proteins. The process of linking amino acids involves a dehydration reaction where a molecule of water is released, allowing the amino acids to bond together. This polypeptide structure ultimately plays a crucial role in numerous biological functions, including enzyme catalysis, providing structure to cells, and facilitating communication within and between cells.

Hormones, carbohydrates, and lipids represent different classes of biomolecules that are formed from other types of building blocks. Hormones can be made from proteins or lipids but are not formed directly from amino acids themselves; carbohydrates are composed of sugars and not amino acids; and lipids are primarily formed from fatty acids and glycerol, rather than amino acids. Hence, the correct answer is that amino acids, when joined together, form a protein.