Which of the following is a basic amino acid?

1. Alanine

2. Tyrosine

3. Lysine

4. Serine 

The non-essential amino acid among the following is:
1. Lysine
2. Valine
3. Leucine
4. Alanine

Which structure(s) of proteins remains(s) intact during denaturation process?

1. Both secondary and tertiary structures

2. Primary structure only

3. Secondary structure only

4. Tertiary structure only