What are proteins primarily composed of?

Proteins are primarily composed of amino acids, which are organic compounds that serve as the building blocks for proteins. Each protein is made up of a specific sequence of amino acids linked together by peptide bonds. There are 20 different amino acids that can be combined in various ways to form the diverse array of proteins necessary for various biological functions.

Proteins play crucial roles in nearly every biological process, including acting as enzymes, structural components, signaling molecules, and transporters. The sequence and types of amino acids determine the protein's structure and function, which is essential for maintaining the organism's health and facilitating metabolic processes.

Other components listed like carbohydrates, vitamins, and nucleotides do not make up proteins. Carbohydrates are primarily energy sources; vitamins serve as cofactors for enzymatic reactions and are not structural components of proteins; nucleotides are the building blocks of nucleic acids, such as DNA and RNA, and do not contribute to protein structure. Therefore, the correct answer highlights the fundamental role of amino acids in protein composition.