The bond that determines the secondary structure of a protein is

Glycine may be classed as all of the following except

$A$ 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:

At which $pOH$ values is the isoelectric point of an amphoteric amino acid typically found?

Haemoglobin is

Proteins are built up of