The primary structure of a protein is the sequence of amino acids that make up the protein. The amino acids are linked together by peptide bonds, and the sequence of amino acids determines the shape and function of the protein. There are 20 different amino acids that can be used to make proteins. Each amino acid has a unique side chain, which gives the protein its specific properties. For example, some amino acids are polar, while others are non-polar. Some amino acids are acidic, while others are basic. The sequence of amino acids in a protein is determined by the DNA of the cell that produces the protein. The DNA code is translated into the amino acid sequence by the ribosome, which is a cellular organelle. The primary structure of a protein serves as a foundation for its higher-order structures, including secondary, tertiary, and quaternary structures.