What are amino acids primarily composed of?

Amino acids, the building blocks of proteins, are primarily composed of carbon, nitrogen, oxygen, and hydrogen. This composition is crucial for their structure and function. Each amino acid has a central carbon atom attached to an amino group (which contains nitrogen), a carboxyl group (which contains oxygen), a hydrogen atom, and a variable side chain or R group that determines the specific characteristics of the amino acid.

The presence of these four elements allows amino acids to form peptide bonds with one another, creating proteins through a process called protein synthesis. This diverse range of amino acids enables the formation of various proteins that perform numerous functions in biological systems, from enzymes to structural components.

The other answer choices do not reflect the complete composition of amino acids. For example, sulfur is not a primary component of all amino acids, and while some amino acids contain sulfur, most commonly in cysteine and methionine, it is not a defining characteristic of amino acids as a whole. Similarly, oxygen and phosphorus, or nitrogen and sodium do not correspond to the basic structural elements of amino acids, reinforcing why the initial choice is the correct one.