Which of the four levels of protein structure is maintained after denaturing?

Primary level

Explanation:

There are four levels in protein structure formation. Primary structure is the most basic one where the amino acids are linked to each other via peptide bonds. It is formed between carboxyl group of one amino acid and amino group of another amino acid. When Hydrogen bonding occurs in this polypeptide chain, secondary structure is formed. It can be of two types alpha helix and beta sheet. Tertiary structure is formed by side chain interactions within the polypeptide. Quarternary structure is formed when two or more polypetide chains interact with each other. Denaturation is able to disrupt various hydrophobic and hydrophilic interactions hence protein's structure is destroyed till secondary level. However it is not able to disrupt peptide bond hence primary structure remains intact.