Protein Structure

Proteins possess four different structures: primary, secondary, tertiary, and quaternary. The unique configurations in each level allow different proteins to function in unique ways. It is important to note the bond types/interactions associated with each level of configuration. The following figure depicts a summary of the information on this page:

Protein Structure
By CNX OpenStax [CC BY 4.0 (http://creativecommons.org/licenses/by/4.0)], via Wikimedia Commons

Primary Protein Structure (1°)

Primary structure refers to the sequence of amino acids joined together by peptide bonds. This is the most basic level of a protein’s structure.

Secondary Protein Structure (2°)

Secondary structure is the way hydrogen bonds cause the polypeptide to fold between the backbone’s NH and CO groups. The most common forms of secondary structure are the α-helix and β-pleated sheet.

Tertiary Protein Structure (3°)

Tertiary structure involves more complicated three-dimension interactions between amino acids more distantly located from each other. These interactions involve side chains of amino acids. The following list summarizes the forces involved in the tertiary structure:

  • Hydrogen bonds between polar side chains.
  • Van der Waals forces between non-polar side chains.
  • Disulfide bonds between two cysteine molecules.
  • Electrostatic forces between acid and basic chains.

Quaternary Protein Structure (4°)

Quaternary structures are interactions between multiple amino acid chains (subunits). The forces involved in the quaternary structure are similar to those of the tertiary structure. For emphasis, they are listed again:

  • Hydrogen bonds between polar side chains.
  • Van der Waals forces between non-polar side chains.
  • Disulfide bonds between two cysteine molecules.
  • Electrostatic forces between acid and basic chains.

 

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