The Stairway To Life: An Origin-Of-Life Reality Check by Change Tan & Rob Stadler

Author:Change Tan & Rob Stadler [Tan, Change]
Language: eng
Format: azw3, epub
Publisher: Evorevo Books
Published: 2020-03-11T16:00:00+00:00

Chapter 14

Means for Repairing Biopolymers

Assuming that the challenges of all prior chapters have been overcome, we have now amassed a significant quantity of prebiotic information stored in molecules. The current abiogenesis story ascribes millions of years, perhaps hundreds of millions of years, for the accumulation of this information. The immensity of deep time plays the role of the protagonist in the drama of abiogenesis. The story goes something like this: the accumulation of information required for each step is highly improbable, but given enough time, anything could happen. Unbeknownst to the playwright, their hero has a dark side: time is a subversive agent intent on destroying—not accumulating—information. Information generally degrades over time. For example, what fraction of literary works have survived from ancient Persia? Similarly, how many people remember what they had for lunch last Monday? Maintenance of information over time requires targeted application of energy. Given a focused application of human energy, more literary works from ancient Persia could have survived. For abiogenesis, maintenance of information over deep time in a prebiotic world would require very specific application of energy to preserve the information despite natural degradative processes.

Within our short lifetime, the information stored in our DNA faces a continuous barrage of attacks from radiation, oxidation, alkylation, chemical mutagens, pathogens, and water. Every day, the DNA in a typical human cell faces an estimated 2,000–10,000 depurinations [110, 111], 600 depyrimidinations [156], 10,000 cases of oxidative damage [157], 55,000 single-strand breaks [158], and 10 double-strand breaks [159].

Molecular Maintenance Plan

Fortunately, living organisms are endowed with a wide variety of specialized DNA repair mechanisms to counteract these daily attacks: base excision repair, nucleotide excision repair, homologous recombination repair, mismatch repair, photoreactivation, nonhomologous end joining, translesion synthesis [160], and processing by the MRN complex [161].35 The base excision repair mechanism (Figure 12) occurs in prokaryotes and eukaryotes and requires the coordinated efforts of at least five enzymes to make small repairs to DNA [110, 162]. The nucleotide excision repair mechanism, also highly prevalent throughout life, targets more extensive damage. In E. coli, nucleotide excision repair requires five enzymes to replace a strip of twelve nucleotides when DNA damage is discovered [163]. These repair pathways preserve information via very specific applications of energy; production and function of the enzymes both require energy.

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