The Incredible Complexity of Protein Sequences

Protein sequences are large bio-molecules consisting of one or more long chains of amino acid residues. There are 20 different amino acids (AA) and this gives rise to an incredible theoretical complexity.

The number of possible combinations is for a protein consisting of

10 AA = 20^10 = 10 billions

20 AA = 10^26

100 AA = 10^130 with the number of atoms in the universe being just 10^82 (one-hundred thousand quadrillion vigintillion atoms)

Consider that the average protein consists of a couple of hundred amino acids. The biggest known proteins are measured in tens of thousands of amino acids. Not to mention post-translational modifications, etc. Yes, that’s how complex life is.

This complexity led researchers in the 70s to believe that our memory was encoded in proteins sequences. They did bizarre experiments (McConnel, 1962) where they trained worms, ground them up, fed them to other worms and see whether the learned behavior is transferred from the trained victim to the naive recipient, and actually showed the trained behavior! Later, this hypothesis turned out to be completely wrong. In fact, synaptic plasticity in synapses between neurons that encodes memory – which is regulated by proteins.

Bottom line: Proteins may not be the real magnetic tapes for our memories and dreams. The idea illustrates the incredible complexity of protein sequences.


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