An Interactive Introduction to Organismal and Molecular Biology, 2021

PROTEIN STRUCTURE AND FUNCTION | 123
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hemoglobin as an example and
describes the molecular structure in
more detail.
As seen in the image above, a strand of amino acids folds on
itself, creating a unique shape in the tertiary structure of the protein. This is caused by the chemical properties
of the amino acids. The chemical properties of the amino acids determine how this shape occurs. For instance,
each amino acid is negatively (-), positively (+), or neutrally (N) charged. Negatively charged amino acids bind
with positively charged amino acids (neutrally charged amino acids are not affected). Also, the amino acid called
cysteine contains sulfur and sulfurs easily bind with each other, creating a “disulfide bond.” Because of this,
cysteines bind with other cysteines. See the table below for a list of all 20 amino acids and their charges. There
are other properties that also influence a protein’s shape, such as the amino acid’s polarity. Note that these bonds
are not as strong as what is created between amino acids when an amino acid chain is created, but these bonds
are strong enough to hold the shape in the protein.