Primary Structure

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Photo by: Andrzej

There are four recognized levels of protein structure: primary, secondary, tertiary, and quaternary. The primary structure refers to the amino acid sequence of a protein. The primary structure is important to the protein's unique three-dimensional structure, its mechanism of action, and its relationship to other proteins with similar physiological roles. The amino acids in a protein✶ are linked together by a specific type of covalent bond , called a peptide bond, that exists between adjacent amino acids in the polypeptide chain. Another important aspect of the primary structure is the sequence or order of amino acids in the polypeptide chain. The sequence of amino acids in a protein is specified by the nucleotide sequence of the segment of DNA containing the gene that codes for that protein. Each protein has a characteristic number and sequence of amino acid residues. The primary structure of a protein determines how the protein folds into a unique three-dimensional structure (further described by the secondary, tertiary, and quaternary structures), which in turn determines the biological function of the protein.

✶ See the Amino Acids article for a table of the amino acids.

Figure 1. Structure of a tripeptide with the peptide bonds marked with an asterisk. The primary sequence is the order of amino acids, and in this example the primary sequence is ala-ser-gly.

SEE ALSO Peptide Bond ; Proteins ; Quaternary Structure ; Secondary Structure ; Tertiary Structure .

Elizabeth S. Roberts-Kirchhoff

Bibliography

Nelson, David L., and Cox, Michael M. (2000). Lehninger Principles of Biochemistry , 3rd edition. New York: Worth Publishers.

Internet Resources

Bragin, Victoria. "Introduction to Protein Structure." Available from http://www.paccd.cc.ca.us .

Gorga, Frank. "Introduction to Protein Structure." Available from http://webhost.bridgew.edu/fgorga .