Which gas is found in the form of proteins in plants and animals?

Identify the acidic amino acid from the following list represented by three-letter symbols.

The list given below contains essential amino acids that are basic $(X)$ and also non-essential amino acids that are neutral $(Y)$. Identify $X$ and $Y$ from the following list:
$a)$ Lysine
$b)$ Alanine
$c)$ Serine
$d)$ Arginine
$e)$ Tyrosine

Which of the following amino acids contains the $HN=C(NH_2)-$ linkage?

In the given pentapeptide, find out an essential amino acid $(Y)$ and the sequence present in the pentapeptide: Choose the correct answer from the options given below:

Write a general introduction and the importance of proteins.