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Name: Abhijit
Status: Other
Grade:  Other
Location: TX
Country: United States
Date: February 2006


Question:
What differences are there in the function of secondary, tertiary and quatenary protein structure?



Replies:
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.)

C. Perkins


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 maintain.tertiary structure.

Ron Baker, Ph.D.



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