Question

Which of the following is NOT an example of secondary structure found in proteins?
A) Random coil
B) Hydrophobic folding
C) -Helix
D) –Pleated sheet

Answer 1

Hint: Secondary structures of proteins are formed by the association of linear chain of the amino acids. They involve the interaction between the carboxyl and amine group of the protein which helps in their association. The secondary structures include alpha helices, beta sheets and coils.

Complete step by step answer:
Now we will discuss in detail about random coils:
A random coil is completely absent in protein structure. In a random coil, peptide bonds only form relationships with adjacent residue of amino acids. As a result, it becomes easier to detect random coils through the absence of the signals in multidimensional nuclear magnetic resonance experiments that depend on interaction of peptide to peptide. Likewise in crystallography experiments the images produced simply show the absence of random coil as an “electron density” or contrast. Dichroism also helps to detect random coils easily in the structure. And protein can be reduced entirely to random coil by Denaturing.
The protein has a normal peptide sequence as in native protein and a random coil only appears after denaturing. The non-polar or hydrophobic folding, alpha helices and beta pleated sheets are present in the secondary structure of protein and they stabilize the secondary structures of a protein.

So, the correct answer is Option A.

Note: alpha-helix is one of the structures of proteins in which hydrogen bonds are formed between $NH$ group of each amino acid and $CO$of the adjacent turn of the helix. They form a twisting structure which looks like the right hand screw.
In beta sheets the polypeptide chain is attached to the adjacent parallel or antiparallel sheet through hydrogen bonding.