$I.$ They activate many enzymes
$II.$ They participate in the oxidation of glucose to produce $ATP$
$III.$ Along with sodium ions, they are responsible for the transmission of nerve signals
Arginine, Phenylalanine, Aspartic acid, Cysteine, Histidine, Valine, Proline
$\begin{array}{*{20}{c}}{CHO}\\|\\{HCOH}\\|\\{HOCH}\\|\\{HCOH}\\|\\{C{H_2}OH}\\I\end{array}$ $\begin{array}{*{20}{c}}{CHO}\\|\\{HCOH}\\|\\{HCOH}\\|\\{HOCH}\\|\\{C{H_2}OH}\\{II}\end{array}$ $\begin{array}{*{20}{c}}{CHO}\\|\\{HCOH}\\|\\{HCOH}\\|\\{HCOH}\\|\\{C{H_2}OH}\\{III}\end{array}$