All proteins found in nature are polymers of the 20 genetically encoded amino-acids that are arranged in specific sequences. Typically, these polymers are called peptides when the number of residues is smaller than 50; longer sequences are called proteins. Even in relatively simple organisms like bacteria, the average protein is composed of 300 amino acid residues. How many possible different sequences of a 300-residue protein can be made using the 20 natural amino acids? Compare this number to the estimated number of grains of sand (10¹⁹) on Earth and the estimated number of atoms in the universe (10⁸⁰).