Learning Goal 5 – The Origin of Cells Conditions of the Early Earth – The Oparin-Haldane Hypothesis – New Theories for the Origin of Life – Protocells – The First Living Cells – The Endosymbiotic Hypothesis – Eukaryote, Bacteria, and Archaean Relationships –

Conditions on Primordial Earth Due to gravitational compression, the internal temperatures of our planet were 1000-3000 degrees Celsius. Metals and heavier substances sank into the core, and lighter substances rose to the surface. The crust formed when the surface cooled and solidified into rocks. The gravitational pull was strong enough to hold an atmosphere, which came partly from the original dust cloud, and from gasses inside of the planets interior. The conditions on primordial life met the basic conditions for life to begin. It was the right distance from the sun for water to stay as a liquid. As earths surface cooled, sources for energy caused chemical bonds to break and form leading to the formation of organic material.

The Oparin-Haldane Hypothesis Initiated Scientific Investigations into the Origin of Life. They hypothesized that earth's atmosphere in the past was different from what it is today. COMPOSED OF HYDROGEN, METHANE, AMMONIA, AND WATER. This gave the primordial atmosphere a reducing character If oxygen was present the newly formed molecules would have been broken down quickly by oxidation. As the surface of Earth cooled again, torrential rains of this mixture formed the first seas, the “primordial soup” Oparin demonstrated that there could have been a great variety of organic compounds before there were living things, as a result of the fact that carbon was first present.

New Theories for the Origin of Life One current theory for the origin of life is that life developed near hydrothermal vents in the sea floor. Many such vents exist in today’s oceans, emitting bursts of mineral-rich water superheated to up 400 C by submarine volcanoes. Scientists exploring hydrothermal vents find complex ecosystems associated with them. Life might have originated there because near oceanic hydrothermal vents reduce conditions that existed there along with an abundance of the chemicals essential for life.

Protocells Definition- A primitive cell-like structure that has some of the properties of life and that might have been the precursor of cells. Made up of only two molecular components: RNA replicase and a fatty acid membrane. It is a extremely simple version of a cell.

The First Living Cells The first living cells may have originated from protocells, very simple versions of regular cells. They would have needed a better information system to properly form into modern cells. The first living cells to form were prokaryotes. They do not contain a nucleus, but had an area where DNA could reside. They also contained ribosomes and the enzymes that are needed to transcribe RNA into amino acid and therefore protein. They also had an oxidation system in their cytoplasm.

The Endosymbiotic hypothesis first postulated by Lynn Margulis in the 1967. Dr. Margulis was doing research on the origin of eukaryotic cells. She proposed that the similarities between prokaryotes and organelles, together with their appearance in the fossil record, could best be explained by "endo- symbiosis". [Endo = "within"] [Endosymbiosis = cells are engulfed, but not digested...cells live together is a mutually benefitting relationship, or symbiosis] Her original hypothesis was that the aerobic (requires oxygen) bacteria was ingested by the anaerobic (poisoned by oxygen) bacteria. Each would have benefiting functions from their symbiosis relationship. The aerobic bacteria would have handled the toxic oxygen for the anaerobic bacteria, and the anaerobic bacteria would ingested food and protected the aerobic

Eukaryote, Bacteria, and Archaean Relationships Eukaryote vs. Achaean Bacteria vs. Archaean Genome organized into a single DNA molecule No nuclear envelope No organelles comparable to mitochondria chloroplast, the ER, or Golgi complex Presence of introns in genes Archeaen Only Cell walls, plasma membrane, gene and rRNA sequences different from all other organisms.

Eukaryotes originally derived from Archaeans?? The Data suggest that though all three domains we have today came from a common ancestor scientist now theorize that Eukaryotes were derived from a common Archean ancestry. Bacteria Eukaryotes Archaeans Common Ancestor