Sample MCAT Question - Protein Denaturation
a) It affects all types of amino acid structures
b) It does not affect protein function
c) It is an irreversible process
d) It cannot break peptide bonds
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Protein Denaturation = Disruption of Folding
Protein denaturation is defined as the disruption of secondary, tertiary, and quaternary structures of a protein. In other words, denaturation is the disruption of protein folding. Since denaturation does not affect peptide bonds, it does not affect primary protein structures. Note that proteins fold and form particular structures to carry out their function. In this way, a protein that is denatured may not function properly.
Temperature, pH, salt concentration, reducing agents
Certain situations or conditions can denature proteins, such as extreme temperature, pH, or salt concentrations. Also, chemical or reducing agents can denature proteins as well. A typical example of a reducing agent is beta-mercaptoethanol, which denatures proteins through the disruption of disulfide bonds. Disulfide bonds form between cysteine residues and are formed by oxidation reactions. So, in order to break disulfide bonds, the opposite of oxidation (reduction) is necessary.
An example of a chemical agent that can denature proteins is urea. Urea contains many groups capable of forming hydrogen bonds. It will disrupt hydrogen bonds on proteins and prevent proteins from forming hydrogen bonds with themselves. In this way, proteins will form hydrogen bonds with urea and unfold. Also, sodium dodecyl sulfate (SDS) is a detergent that can denature proteins as well. As a detergent, SDS breaks down and disrupts many interactions in proteins and causes them to unfold. SDS is useful in laboratory techniques like gel electrophoresis (specifically SDS-PAGE) because in denaturing proteins, it gives them an overall negative charge, thus allowing the experimenter to eliminate the effect of charge during electrophoresis and therefore separate proteins based on size alone.
It is important to note that although all of these methods can denature a protein, sometimes it is more effective to use more than one at the same time. For example, in some gel electrophoresis experiments, both SDS and the reducing agent beta-mercaptoethanol are utilized simultaneously, leading to more effective protein denaturation.
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MCAT Masterclass Chapters
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Levels of Protein Structure
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Post-Translational Modification of Proteins
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Gel Electrophoresis, PAGE, SDS- PAGE
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Ribosome Structure & Function
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Mutations
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The Genetic Code
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