Which substance is composed of chains of amino acids and contains carbon, hydrogen, oxygen, and nitrogen?

The correct response is based on the unique structure of proteins. Proteins are macromolecules that are composed of long chains of amino acids linked together by peptide bonds. Each amino acid contains a central carbon atom, an amino group (which includes nitrogen), a carboxyl group, a hydrogen atom, and a variable R group or side chain that determines the characteristics of each amino acid.

Proteins are crucial for many biological functions, including acting as enzymes, providing structural support, and regulating biological processes. The presence of carbon, hydrogen, oxygen, and nitrogen is distinctive to proteins, as these elements combine to create the amino acids that serve as the building blocks of proteins.

Other substances listed have different compositions. For example, carbohydrates are primarily made of carbon, hydrogen, and oxygen in a ratio that typically features a hydrogen to oxygen ratio of 2:1. Lipids mainly consist of carbon and hydrogen, with some oxygen but lack nitrogen. Nucleic acids, such as DNA and RNA, are composed of nucleotide units that include a sugar, phosphate group, and nitrogenous base, but do not consist of chains of amino acids. Thus, the composition of proteins with amino acid chains and the inclusion of nitrogen makes them unique among these options.