Yes they can have origins in nature. A bunch of the elements on the periodic table are chemicals and this are basic substances and cannot be man made.
Answer:
The same element that contain equal number if protons but different number of neurons in their nuclei and hence differ in relative atomic mass
In nature there are many more variations amino acids than the simple 20 found in humans. However, when analyzing the human genome sequence, there is a code for all 64 permutations (4^3), only some of them share amino acids. This is a safe-guard against mutations of one or two nucleotides. For example, the amino acid Alanine is coded with four different nucleotide sequences: GCA, GCC, GCG, GCU. Also some amino acids code the same like UUU &UUC