The pair in which both species have iron is

Consider the following statements:
Statement-$I$: The primary structure of a protein represents its amino acid sequence.
Statement-$II$: The $\alpha$-helix and $\beta$-pleated sheet structures of a protein represent its tertiary structure.

The isoelectric point of alanine is $pH = 6$. At which $pH$ will the maximum concentration of the zwitterion of alanine be present?

In the given pentapeptide, find out an essential amino acid $(Y)$ and the sequence present in the pentapeptide: Choose the correct answer from the options given below:

Identify the correct statement among the following $:$

During denaturation, which level of protein structure remains unchanged?