The Structure of Proteins
We have already discussed that proteins are complex biomolecules made up of many small units called amino acids. These amino acids are linked by peptide bonds to form long polypeptide chains. The specific order of these amino acids determines the structure and function of proteins. The long chains of amino acids folded into a three-dimensional structure is what we call the functional protein. In this section we explore the different levels of structure of proteins.
The primary structure of a protein is the unique sequence of amino acids which determines the shape and function of the protein. in the previous topic we looked at the chemical properties of amino acids. The chemical properties determine how the polypeptide chains bend, twist, and fold.Â
The Secondary structure refers to the arrangement of amino acids in space and is a function of the angles formed by the peptide bonds. Helical and zigzag structures are examples of secondary structures.
The tertiary structure refers to how the various helical, zigzag, and less ordered regions of a polypeptide chain fold back upon themselves to form a compact, spherical, or globular shape. Tertiary structure is determined largely by the side chains of the amino acids. Side chains that carry opposite electrical charges attract one another and form ionic bonds; those with like electrical charges repel one another. Permanent hair waving is achieved by altering the tertiary structure of a protein in hair. Quaternary structure refers to the way in which several different polypeptide chains assemble into larger protein complexes.
Quaternary structure refers to the way in which several different polypeptide chains assemble into larger protein complexes.
Some proteins are oligomeric: composed of more than one polypeptide chain. For example, Hemoglobin is made up of four polypeptide chains: two alpha and two beta chains that fit together with four heme groups in a quaternary structure.
