Chapter 14 — The Impossible Odds

A functional protein requires not just any amino acid sequence—it requires the right sequence, folded into the right three-dimensional shape. Most random amino acid chains do not fold into stable, functional structures. The sequence space for a 150-amino-acid protein is 20 raised to the 150th power—approximately 10195—possible sequences. Only a tiny fraction fold correctly and perform a biological function.

In 2004 Douglas Axe of the Biologic Institute published research in the Journal of Molecular Biology measuring how rarely functional enzyme folds appear in that space. His result: approximately 1 functional fold per 1077 possible sequences of 150 amino acids. For reference, the estimated number of atoms in the observable universe is approximately 1080. The functional fold ratio approaches that number from three orders of magnitude below it.

Stephen Meyer extended the calculation in Signature in the Cell (2009), accounting for the additional requirements of solubility, stability, and biological function. His estimated probability for a 150-amino-acid functional protein arising by chance: approximately 1 in 10164. The total number of trials available if every atom in the universe had been randomly assembling amino acid chains since the Big Bang is approximately 1093—seventy-one orders of magnitude short of the less stringent estimate. The protein problem alone is sufficient to rule out an unguided origin of life.

Axe, D.D. "Estimating the Prevalence of Protein Sequences Adopting Functional Enzyme Folds." Journal of Molecular Biology 341 (2004): 1295–1315. Meyer, S.C. Signature in the Cell: DNA and the Evidence for Intelligent Design. HarperOne, 2009. Chapter 9.

Chapter 15 — Light-Harvesting

Photosynthesis powers almost all life on earth. The light-harvesting complexes of photosynthetic organisms capture photons and funnel their energy to reaction centers with an efficiency that has no parallel in human engineering. Antenna complexes containing chlorophyll and carotenoid molecules arranged in geometrically precise arrays absorb photons and transfer energy to the reaction center.

In 2007 Graham Fleming's group at UC Berkeley published evidence in Nature that this energy transfer proceeds with quantum coherence. The energy does not hop randomly from molecule to molecule. It explores multiple pathways simultaneously through a quantum mechanical process and finds the most efficient route to the reaction center in femtoseconds—quadrillionths of a second. The efficiency of this process in some systems approaches 95 percent—far beyond what classical physics predicts and far beyond what human photovoltaic engineering has achieved.

The light-harvesting complex requires the precisely arranged array of pigment molecules, the protein scaffold holding them in exact positions, the reaction center to which energy is delivered, and the downstream chemistry converting excitation energy into chemical energy. The quantum coherence mechanism depends on the geometric precision maintained by the protein scaffold. Remove any component and there is no energy transfer. Human attempts to replicate artificial light-harvesting at this efficiency have not succeeded.

Engel, G.S. et al. "Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems." Nature 446 (2007): 782–786. Blankenship, R.E. Molecular Mechanisms of Photosynthesis, 2nd ed. Wiley-Blackwell, 2014.