Denaturation (biochemistry)

Process of partial or total alteration of the native secondary, and/or tertiary, and/or quaternary structures of proteins or nucleic acids resulting in a loss of bioactivity.

[1] Note 2: Denaturation can occur when proteins and nucleic acids are subjected to elevated temperature or to extremes of pH, or to nonphysiological concentrations of salt, organic solvents, urea, or other chemical agents.

[2] In biochemistry, denaturation is a process in which proteins or nucleic acids lose folded structure present in their native state due to various factors, including application of some external stress or compound, such as a strong acid or base, a concentrated inorganic salt, an organic solvent (e.g., alcohol or chloroform), agitation and radiation, or heat.

[4][5] Denatured proteins can exhibit a wide range of characteristics, from conformational change and loss of solubility or dissociation of cofactors to aggregation due to the exposure of hydrophobic groups.

However, hydrogen bonds and cofactor-protein binding, which play a crucial role in folding, are rather weak, and thus, easily affected by heat, acidity, varying salt concentrations, chelating agents, and other stressors which can denature the protein.

The cold appetizer known as ceviche is prepared by chemically "cooking" raw fish and shellfish in an acidic citrus marinade, without heat.

A protein is created by ribosomes that "read" RNA that is encoded by codons in the gene and assemble the requisite amino acid combination from the genetic instruction, in a process known as translation.

The newly created protein strand then undergoes posttranslational modification, in which additional atoms or molecules are added, for example copper, zinc, or iron.

[9] Consequently, any exposure to extreme stresses (e.g. heat or radiation, high inorganic salt concentrations, strong acids and bases) can disrupt a protein's interaction and inevitably lead to denaturation.

This is in contrast to intrinsically unstructured proteins, which are unfolded in their native state, but still functionally active and tend to fold upon binding to their biological target.

[14] These metals, when interacting with native, folded proteins, tend to play a role in obstructing their biological activity.

[14] Heavy metals also play a role in oxidizing amino acid side chains present in protein.

Following 5'-3' synthesis of the backbone, individual nitrogenous bases are capable of interacting with one another via hydrogen bonding, thus allowing for the formation of higher-order structures.

Nucleic acid denaturation occurs when hydrogen bonding between nucleotides is disrupted, and results in the separation of previously annealed strands.

[20] However, the Poland-Scheraga Model is now considered elementary because it fails to account for the confounding implications of DNA sequence, chemical composition, stiffness and torsion.

[24] These chemical denaturing agents lower the melting temperature (Tm) by competing for hydrogen bond donors and acceptors with pre-existing nitrogenous base pairs.

For example, alkaline agents (e.g. NaOH) have been shown to denature DNA by changing pH and removing hydrogen-bond contributing protons.

[30] As a result, DNA strands exposed to air require less force to separate and exemplify lower melting temperatures.

The effects of temperature on enzyme activity.
Top : increasing temperature increases the rate of reaction ( Q10 coefficient ).
Middle : the fraction of folded and functional enzyme decreases above its denaturation temperature.
Bottom : consequently, an enzyme's optimal rate of reaction is at an intermediate temperature.
(Top) The protein albumin in the egg white undergoes denaturation and loss of solubility when the egg is cooked. (Bottom) Paperclips provide a visual analogy to help with the conceptualization of the denaturation process.
Functional proteins have four levels of structural organization:
  1. Primary structure: the linear structure of amino acids in the polypeptide chain
  2. Secondary structure: hydrogen bonds between peptide group chains in an alpha helix or beta sheet
  3. Tertiary structure: three-dimensional structure of alpha helixes and beta helixes folded
  4. Quaternary structure: three-dimensional structure of multiple polypeptides and how they fit together
Process of denaturation:
  1. Functional protein showing a quaternary structure
  2. When heat is applied it alters the intramolecular bonds of the protein
  3. Unfolding of the polypeptides (amino acids)
DNA denaturation occurs when hydrogen bonds between base pairs are disturbed.
Formamide denatures DNA by disrupting the hydrogen bonds between base pairs. Orange, blue, green, and purple lines represent adenine, thymine, guanine, and cytosine respectively. The three short black lines between the bases and the formamide molecules represent newly formed hydrogen bonds.