Which of the following best describes polypeptides?

Polypeptides are best described as consisting of amino acids linked by peptide bonds. This definition captures the fundamental structure of polypeptides, which are polymers formed from chains of amino acids. Each amino acid in a polypeptide is connected to the next through a specific type of covalent bond known as a peptide bond. This bond forms through a dehydration synthesis reaction between the amino group of one amino acid and the carboxyl group of another.

Understanding this is critical because it emphasizes the importance of the sequence and chemical properties of the amino acids, which ultimately determine the polypeptide's structure and function. The unique properties of polypeptides give rise to a wide variety of biological functions in organisms, from serving as enzymes to providing structural support.

The other choices refer to different macromolecules: monosaccharide units are related to carbohydrates, nucleotide sequences pertain to nucleic acids like DNA and RNA, and fatty acid chains are components of lipids. Each of these structures has distinct functions in biological systems, which underscores the importance of recognizing the specific characteristics that define polypeptides.