Research in the last two centuries has caused dramatic shifts in perspectives on the origin and evolution of life. The building blocks of life include lipids, amino acids, nucleic acids, and carbohydrates. Origin of life research seeks to identify the processes that formed these organic compounds and the ways in which these compounds formed protocells. The origin of life probably took place 3.85 Ga. Early life was dominated by light harvesting organisms. Algae and plants evolved over the next 3.3 billion years of the Archaean and Proterozoic eons.
Prior to 1859, when Louis Pasteur proved that life could only come from life, almost all people (scientists, theologians, and the public) thought that life spontaneously arose from nonlife. Then, from 1859 to the early 20th century, almost all people thought that cells must have been created de novo by God and that life either evolved from these first cells or that God created different forms of life. In 1924, Oparin provided a theoretical justification for biochemical evolution and began the quest to find a natural origin of life (Section 6-2). In 1952, Miller and Urey applied electricity for several days to a mixture of H2O, H2, CH4, and NH3 gases and produced amino acids, nucleobases, and fatty acids. When scientists realized that RNA could act like DNA (information storage) and proteins (work), Crick, Orgel, and Woese proposed that life began with the RNA world in the 1960s. Since the 1990s, Jack Szostak’s laboratory has investigated the formation of life in naturally occurring fatty acid vesicles. Finally, in 2009, Sutherland’s lab discovered how sugars and RNA nucleotides might form in cyanosulfidic chemistry, and we reached the “end of the beginning.” Almost a century has passed, and there is still a long way to go, but scientists are rapidly discovering new pieces and patterns in the origin of life. This jigsaw puzzle is slowly coming together; however, as with a jigsaw puzzle, scientists might find as the puzzle comes together that a few pieces are missing from the puzzle. Will they find a finely tuned process or a gap in the sequence of evolution that defies a natural explanation?
Section 6-3 describes the organic compounds that came together and formed early protocells and then became the building blocks of modern cells: carbohydrates, lipids, proteins, and nucleic acids.
After Miller and Urey discovered that amino acids, the building blocks of proteins, form in chemical reactions, scientists worked for decades to discover a prebiotic process that formed sugars (carbohydrates), which are one of the building blocks of nucleic acids. Finally, in 2009, the Sutherland laboratory discovered cyanosulfidic chemistry, which preferentially forms all the organic compounds of life (Section 6-4)
What came first, the chicken or the egg? In biological evolution, a similar question was, what came first, information storage or cellular processes? Researchers were excited to discover that RNA could act as a machine in the cell (protein) as well as an information storage system (DNA). Thus, they proposed the RNA world in which life began with RNA. Section 6-5 presents a brief review of the functions of RNA in modern cells and the research on how functional chains of RNA might have evolved in the prebiotic soup.
Fatty acid vesicles are like cellular membranes, and their presence in meteorites indicates they naturally formed in the early environment of the Earth and solar system. There are various theories on how these bubbles with water on both sides of the membrane might have formed the first protocells, contained RNA and other organic compounds, and how they might have divided and evolved. Section 6-6 presents the work of Jack Szostak, the leading researcher in this field, and of biologist Bruce Damer, who have both proposed hypothetical scenarios that might have formed the first protocells.
Scientists look at ancient archaebacteria in toxic pools in Yellowstone for clues to the structure of early cells. Section 6-7 describes the light harvesting system in Halobacterium halobium. These simple bacteria utilize the photons in light to push protons outside the cell, which then flow back into the cell through ATP synthase, which provides energy for cellular functions (work) by converting ADP to ATP.
Photosynthesis became much more efficient and complex in cyanobacteria, which had the same photosynthetic systems as green algae and modern plants. Many scientists think that this increase in efficiency is connected to the Great Oxidation event 2.5 billion years ago. Cyanobacteria still supply approximately half of the world’s oxygen. Section 6-7 describes the photosynthetic systems in blue-green algae (cyanobacteria), green algae, and plants.
Section 6-9 describes the fossil record of algae and plant evolution. Approximately 1.9 billion years ago, blue green algae were adsorbed into eukaroyote cells with a nucleus and became the organelle in provides energy through photosynthesis in larger cells. Eventually green algae evolved, which then evolved into two and three dimensional plant structures in the sea and then transitioned to land as moss and other bryophytes. Plants then evolved into the ferns, gymnosperms (pine trees) and angiosperms (flowering plants) of the modern world.
In the excursus (Section 6E, optional), Moses describes the natural origin and evolution of photosynthetic life on earth.
Naturally forming fatty acid vesicle composed of fatty acids with hydrophobic tails and hydrophilic heads It is the same structure as cellular membranes.