How is it possible that over 20 million living organisms on the planet are made up of only 5 types of nucleotide based arranged in long chains?

Answer/Explanation:

The DNA in all living organisms is made up of 4 bases, adenine, thymine, guanine, cytosine. The RNA replaces thymine with uracil, making 5 types of nucleotide. The number of nucleotide pairs in a genome can range from half a million up to 100,000 million - meaning there are an exponential number of combinations of these 4 bases.

Imagine an organism exists that has only 2 nucleotides (this is over 200,000x smaller than even the smallest bacterial genome). If we allow any nucleotide at each of the 2 positions, then we have 4x4 (4²) or 16 possible combinations of sequences. For a nucleotide length of 4, the total number of possible combinations are 4⁴ or 256.

Since we are dealing with many millions of nucleotides, there are essentially infinite combinations of nucleotides, giving rise to the variation that produces over 20 million organisms on the planet.

cell regulation is conducted by special proteins.