The number of tripeptides formed by $3$ different amino acids using each amino acid once is.................

$A$ tetrapeptide $x$ on complete hydrolysis produced glycine $(Gly)$,alanine $(Ala)$,valine $(Val)$,and leucine $(Leu)$ in equimolar proportions. The number of possible tetrapeptide sequences involving each of these amino acids exactly once is:

Explain the types of protein structures based on the provided image.

Identify the incorrect statement about the tertiary structure of proteins.

The increasing order of $pKa$ of the following amino acids in aqueous solution is $Gly, Asp, Lys, Arg$.

In which of the following processes does protein $NOT$ participate?