The tripeptide present in most living cells is

No cell could live without

The triple helical structure of collagen was published in Nature in $1954$, and the analysis of the allowed conformations of proteins was performed through the use of the:

$A$ - In the solution of different $pH$,the structure of amino acids changes.
$R$ - It is because of the ionisable nature of $-NH_2$ and $-COOH$ groups.

Which of the following is the least likely to be involved in stabilising the three-dimensional folding of most proteins?

Amino acids that are not synthesized in the body are called ...... .