What is formed when multiple amino acid molecules join together by forming peptide bonds?

In glycine,the $R$ group is replaced by

The essential element for all living organisms is ........

$A$: Tertiary structure of protein molecules makes them biologically active.
$R$: It is the native configuration of protein molecules maintained by multiple covalent bonds only.

An example of a protein with a quaternary structure is

Which of the following statements are correct regarding amino acids?
$A$. They are substituted methanes.
$B$. Serine is an aromatic amino acid.
$C$. Valine is a neutral amino acid.
$D$. Lysine is an acidic amino acid.
Choose the correct answer from the options given below: