Denaturing and Folding

Topic: The Three Dimensional Protein Structure

Proteins can change their shape and may become unfolded and therefore dysfunctional (denatured) when exposed to different chemicals, pH, or temperatures.

A protein’s function depends on the interactions within its folded structure. If the protein is subject to changes in temperature or pH, or exposed to certain chemicals, the internal interactions between the protein’s amino acids can be altered, which may change the 3D shape/folding of the protein (tertiary structure). Although the amino acid sequence (also known as the protein’s primary structure) does not change, the protein’s shape or the way it is folded may change to an extent that it becomes dysfunctional, in which case the protein is considered denatured. In the cell, chaperone proteins facilitate proper folding and conformation of other proteins.

It is often possible to reverse denaturation because the primary structure of the polypeptide, i.e., the covalent bonds holding the amino acids in their correct sequence, is intact. Once the denaturing agent is removed, the original interactions between amino acids return the protein to its original conformation and it can resume its function. However, denaturation can be irreversible in extreme situations, like frying an egg. The heat from a pan denatures the protein in the liquid egg white and it solidifies.


Practice Questions

 

Khan Academy

 

MCAT Official Prep (AAMC)

Section Bank C/P Section Passage 9 Question 69

Biology Question Pack, Vol. 1 Question 60

Practice Exam 1 B/B Section Passage 1 Question 6

 

Key Points

• Proteins change their shape and may become dysfunctional (denatured) when exposed to different chemicals, pH, or temperatures.

• Some proteins can refold after denaturation while others cannot.


Key Terms

tertiary structure: the overall 3D structure of a polypeptide, which results from ‘folding’ of the peptide chains to allow for interactions between the R group side chains.

denaturation: the change of folding structure of a protein (and therefore its physical properties and function), which may be caused by heating, changes in pH, or exposure to certain chemicals.

chaperones: a class of proteins that facilitate the proper folding and conformation of other proteins



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