Denaturation of Proteins and Its Causes

Denaturation of proteins refers to the alteration of a protein's native conformation, resulting in a loss of biological activity. This structural change occurs without breaking the peptide bonds that form the primary structure. Instead, denaturation disrupts the secondary, tertiary, and quaternary structures, which are stabilized by non-covalent interactions such as hydrogen bonds, ionic bonds, and hydrophobic interactions.

1.0Molecular Formula and Composition

While “molecular formula” varies protein to protein, broadly proteins are polymers formed from amino acids. Key points:

• Amino acids are the monomer units. Each amino acid has a general formula:
  NH₂−CH(R)−COOHNH_2​−CH(R)−COOH
  where R is a side chain.
• Proteins are composed of one or more polypeptide chains, each chain being a sequence of amino acids linked by peptide bonds (–CONH–).
• Proteins fold into secondary (α-helix, β-pleated sheets), tertiary (3D folding via side chain interactions), and often quaternary structures (more than one polypeptide chain).
• The stability of the folded structures depends on weak bonds/forces: hydrogen bonds, ionic (electrostatic) interactions, hydrophobic interactions, van der Waals forces, disulfide bonds (in some proteins).

This molecular composition and folding behavior is critical for understanding what causes denaturation of proteins and what is the effect of denaturation on the structure of proteins.

2.0Preparation and Synthesis Methods

Although proteins are synthesized biologically (in ribosomes, from mRNA templates) rather than via “chemical preparation” in standard JEE chemistry labs, for this topic it's useful to note:

• In vitro synthesis / isolation of proteins from natural sources (cells, tissues) often involves purification steps, buffer solutions, controlled pH, temperature, etc. These must be gentle to avoid denaturation.
• Denaturation is unwanted during extraction, purification, and storage of proteins, so methods aim to maintain native structure: control temperature, avoid extremes of pH, use stabilizing agents (salts, osmolytes) etc.
• Renaturation: in some cases, proteins that have been denatured can be refolded (renatured) under suitable conditions, but only if the primary structure is intact and the denaturing conditions are not too harsh.

3.0Causes of  Denaturation 

Protein denaturation is caused by external factors or agents that disrupt the weak forces that maintain the secondary, tertiary, and quaternary structures of proteins. The main causes include:

4.0Effects of Denaturation 

• Secondary structure loss: α-helices and β-sheets unfold, converting into random coils. 
• Tertiary structure disruption: Side chain interactions (hydrophobic patches, salt bridges, disulfide bonds) are broken or reorganized. Protein may unfold or collapse, exposing hydrophobic regions to solvent. 
• Quaternary structure dissociation: If protein has multiple polypeptide units, these may dissociate; the spatial arrangement between subunits is lost. 
• No change to primary structure: Peptide bonds generally remain intact, so the sequence of amino acids is preserved. 
• Loss of function: Enzymatic activity lost, binding sites no longer correctly shaped, solubility often decreases, and the protein may aggregate or precipitate.

Examples

• Cooking Eggs: Heating causes egg white proteins to denature and coagulate, changing from a clear to a white, solid state.
• Milk Curdling: The addition of acidic substances denatures casein proteins, leading to curd formation.
• Fever: Elevated body temperatures can denature enzymes, affecting metabolic processes.
• Disinfection: Alcohol-based sanitisers denature microbial proteins, leading to cell death.

5.0Laboratory Techniques Involving Protein Denaturation

• SDS-PAGE: Sodium dodecyl sulfate (SDS) denatures proteins and imparts a uniform negative charge, enabling separation by molecular weight during electrophoresis.
• Western Blotting: Involves denaturation of proteins to facilitate transfer and detection.
• Protein Purification: Denaturation and renaturation steps are often employed to refold proteins into their functional forms.