Early Earth and the Origin of Life Part 2 Created by: Sara Khan, Saba Mashhadialireza, and Joey Ricci

RNA was probably the first genetic material Protobionts (aggregates of abiotically produced molecules) that are most stable and best able to accumulate organic molecules from the environment would grow and split- making “baby” droplets The more this happened, the more diluted the molecules would become What is missing here?

HEREIDITY is missing Genetic information would make it possible for molecular aggregates to pass along not just samples of key molecules, but also instructions for making more of those molecules The first genes were not DNA molecules but short strands of RNA that began self-replicating in the prebiotic world This was before the present day idea of DNA  RNA  protien mechanism.

Natural Selection on the molecular level Observed in the lab RNA molecules may have undergone natural selection as those molecules with the most stable three dimensional conformations and greatest autcatalytic activity within a particular environment successfully compete for monomers and generated families of similar sequences. RNA-directed protein syntheses may begun with the weak binding of specific amino acids to bases along RNA molecules and their linkage to form a short polypeptide.

Abiotic replication of RNA Short polymers of ribonucleotides have been produced abiotically in lab experiments If you add RNA to a solution containing monomers for making more RNA, the sequences of nucleotides long are copied from the template according to the base-pairing rules Proteins are not the only the only biological catalysts, so is RNA 1980, Thomas Cech found that modern cells use RNA catalysts, called ribozymes, to do things like remove introns from RNA This is what the world may have been in early periods in the evolution of life when RNA molecules served as both rudimentary genes and organic catalysts

Protobiont When these early RNA and polypeptide molecules became packaged into protobionts, molecular cooperation could become more effeicent More effeicent due to Concentrations of components and the potential for the protobiont to evolve as a unit

The Origin of hereditary info. Made Darwinian evolution possible Protobionts use enzymes to make polymers and perform other chemical processes. They grow and split and distribute genes to the resulting cells, or offspring. The mutations which occur during this process would contribute to variation among the protobionts.

Through evolution, DNA became the hereditary material because it is more stable than RNA. RNA then started to function the way we see it today.

Debate About the Origin of Life Researchers can’t prove and therefore still question the concept of abiotic synthesis of organic monomers. Another idea about the origin of life, called panspermia, is that organic compounds were brought to Earth by comets and meteorites.

Amino acids have been found in meteorites and researchers recently found that the organic material in meteorites form vesicles when mixed with water. Panspermia, however, is only believed to be a minor contributor to the origin of life. Other scientists also believe that RNA is too complex for the very first self-replicating molecules.

Earth’s inhospitable surface around the time life began suggests that, contrary to a traditional belief, the beginning of life took place in the deep sea vents in the ocean. Scientists have found acetyl-coA and iron and nickel sulfides at these locations, which are essential to cell activity.

The discovery of ice on one of Jupiter’s moons and possibly fossilized prokaryotes on an asteroid suggest that life is not limited to our planet alone. It is not yet evident whether life ever evolved on Mars or any other planet. Regardless of when or where life evolved, it is clear that all the lineages of life arose from the prokaryotes that lived at least 3.5 billion years ago on Earth.

The Major Lineages of Life

Arranging the diversity of life into the highest taxa is a work in progress common to be known that there is only two kingdoms: animals and plants Why? because we rarely see organisms that don't fit into the plant/animal group examples: bacteria placed in plant kingdom, Eukaryotic unicellular organism with chloroplasts considered as plants, fungi also considered as plants though they sedentary and aren't photosynthetic nor are structurally close to green plants unicellular creatures that moved or ingest food were considered in the animal kingdom Microbes such as Euglena are photosynthetic though move were in both kingdoms

5 kingdom system Whittaker designed 5 kingdoms: Monera, Protista, Plantae, fungi and Anamalia 2 fundamentally different types of cells: prokaryotic and eukaryotic and they are separated into their own kingdoms Monera is the kingdom with all prokaryotes 3 kingdom for multicellular eukaryotes: Plantae, Fungi, and Anamalia

5 kingdoms in more detail Plants, fungi and Animal all differ in structure, life cycles, and mode of nutrition a. Plants are autotrophic and make food through photosynthesis b. fungi are heterotrophic and are absorptive for their food, as well as decomposers c. animals live by ingesting food and digesting it within specialized cavities Protista - contains all eukaryotes that didn't fit in the definition of plants, fungi or animals and most are unicellular even though few multicellular organisms are descendants of unicellular protists

Point of this system is an attempt to order the diversity of life into a scheme that is useful and reasonable problem with the 5 kingdom classification system has arrived through systematic using comparisons of nucleic acids and proteins do probe relationships between groups super kingdom level: domains of Bacteria, Archaea, and eukarya

Conclusion Classifying life is a work in progress evolving view of biodiversity reflect our increased understanding of characteristics and evolutionary histories of different organisms prokaryotes are the first form of life and only ones for at least 2 billion years which leads us into the next chapter of the diversity and history of prokaryotic life