Which synthesis was done by Stanley Miller?

Which of the following is not an amino acid?

Which of the following statements correctly describes the migration aptitude of aspartic acid during electrophoresis?
$(pK_1 = 2.0, pK_2 = 3.90, pK_3 = 10.0)$
$HOOC-CH_2-CH(NH_2)-COOH$

Protein found in a biological system with a unique three-dimensional structure and biological activity is called a native protein. When a protein in its native form is subjected to a physical change like a change in temperature or a chemical change like a change in $pH$,denaturation of proteins takes place. Explain the cause.

$A$ peptide synthesized by the reactions of one molecule each of Glycine,Leucine,Aspartic acid and Histidine will have ..... peptide linkages.

Which type of linkage is present in the structure of proteins?