Protein Structure Functions
Country: United States
Date: February 2006
What differences are there in the function of
secondary, tertiary and quatenary protein structure?
A protein's overall 3-dimensional shape determines how it interacts with
other molecules. That interaction is its function. So the question is: how
do these levels of protein structure affect the overall 3-d shape? The
simplest answer is that each level depends strongly on the level below
it. The primary structure (the sequence of amino acids) determines how the
chain twists and turns. The secondary structure (the twists turns)
determines the 3-d shape of each piece of a large protein. Finally, the
tertiary structure (the 3-d shapes) determines how those pieces fit together
to make a large protein with a highly specific overall 3-d shape. This is
the quaternary structure.
The four levels are intimately tied together and a protein's function
depends on all of them. If you are thinking about a protein's function,
then it makes no sense to think about one of these structural levels by
itself. They have to be considered together.
(By the way, "quaternary" is one of the most commonly misspelled and
mispronounced words in biology. The preferred pronunciation among
scientists is quaTERnary.)
The primary structure is defined as the specific amino acid sequence of the
protein and is maintained by covalent bonds between the amino group of one
amino acid and the carboxyl group of the adjacent amino acid. The secondary
structure is usually an alpha-helix and is the 3 dimensional shape of the
backbone of the polypeptide. The secondary structure if maintained by
Hydrogen bonds between one amino acid and the amino acid 3 positions away.
The tertiary sequence is the way in which the polypeptide folds up. For most
proteins it is a globular shape held together by a combinatiion of
di-sulfide bonds, H-bonds, oppositely charged ionic bonds and hydrophobic
interactions between non-polar amino acids. Quaternary structure is when two
or more polypeptides bond together to form a dimer or multimer protein.
Quaternary structure is maintained by the same types of bonds that
Ron Baker, Ph.D.
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Update: June 2012