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Name: Christine
Status: Other
Grade:  Other
Location: N/A
Country: United States
Date: May 2005


Question:
Why do proteins adopt a particular folded structure?



Replies:
The way a protein folds (its tertiary structure) is determined by its amino acid sequence (primary structure) and the laws of thermodynamics (the lowest energy state). This folding occurs spontaneously as demonstrated by Christian Anfinsen back in the early 60's. Anfinsen showed that if you heat denaure (unfold) RNAse by boiling, it loses all its enzyme activity, but if you allow it to cool gradually, it regains full activity indicating that if refolds completely on its own, i.e. spontaneously. Anfinsen eventually received the Nobel prize for his work. If you are wondering where secondary sructure comes in, for most globular proteins (enzymes, antibodies and carrier proteins, for example), 90% of their secondary structure is in the form of an alpha-helix.

Ron Baker, Ph.D.


Proteins are made up of amino acids. There are 20 different amino acids. Each of the 20 amino acids has a distinct character: some are positively charged, some negatively charged, some polar, some non polar, etc. The final shape of a protein is the sum total of all of the interactions among the different amino acids, and between the amino acids and the surrounding environment. For example, a non polar amino acid does not interact stably water, and hence will often be found buried deep within the protein. Charged amino acids attract others with the opposite charge, while repelling those with the same charge. Add up all these interactions, and you get the final folded shape of a protein.

Paul Mahoney, PhD


I'm sure you know that proteins are long chains of amino acids. All amino acids have 3 basic parts: the amino group, the acid group and a side group. The amino and acid groups are the same for all amino acids, hence the name. What makes one different from another is the side group. Side groups can be positively charged, negatively charged, acidic, basic, hydrophillic (mix with water) hydrophobic (don't mix with water) and some have sulfur in their structure. Because they each have unique chemical properties, they can interact with each other. So DNA directs the order that the amino acids will come in, and then the side groups start being attracted or repelled by each other. This causes the protein chain to begin to fold in on itself and take a three dimensional shape. Since the order of the amino acids determines which are in proximity to each other and therefore how they will interact, any change in the order of the amino acids will affect that interaction and therefore the shape of the protein.

vanhoeck



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