Which one of the following is an essential amino acid?

The correct zwitter ion structure of glycine is

Amino acids are the building blocks of

Identify the essential amino acids from below $:$
$(A)$ Valine
$(B)$ Proline
$(C)$ Lysine
$(D)$ Threonine
$(E)$ Tyrosine
Choose the correct answer from the options given below $:$

Which of the following is an essential amino acid?

Which compound can exist in a dipolar (zwitter ion) state?