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First Universal Common Ancestor
The first universal common ancestor (FUCA) is a proposed non-cellular entity that was the earliest organism with a genetic code capable of biological translation of RNA molecules into peptides to produce proteins. Its descendents include the last universal common ancestor (LUCA) and every modern cell. FUCA would also be the ancestor of ancient sister lineages of LUCA, none of which have modern descendants, but which are thought to have horizontally transferred some of their genes into the genome of early descendants of LUCA. FUCA is thought to have been composed of progenotes, proposed ancient biological systems that would have used RNA for their genome and self-replication. By comparison, LUCA would have had a complex metabolism and a DNA genome with hundreds of genes and gene families. Origins Long before the appearance of compartmentalized biological entities like FUCA, life had already begun to organize itself and emerge in a pre-cellular era known as the RNA wo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Non-cellular Life
Non-cellular life, or acellular life is life that exists without a cellular structure for at least part of its life cycle. Historically, most (descriptive) definitions of life postulated that an organism must be composed of one or more cells, but this is no longer considered necessary, and modern criteria allow for forms of life based on other structural arrangements. The primary candidates for non-cellular life are viruses. Some biologists consider viruses to be organisms, but others do not. Their primary objection is that no known viruses are capable of autonomous reproduction: they must rely on cells to copy them. Engineers sometimes use the term "artificial life" to refer to software and robots inspired by biological processes, but these do not satisfy any biological definition of life. Viruses as non-cellular life The nature of viruses was unclear for many years following their discovery as pathogens. They were described as poisons or toxins at first, then as "infectio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RNA Replicator
The RNA world is a hypothetical stage in the evolutionary history of life on Earth, in which self-replicating RNA molecules proliferated before the evolution of DNA and proteins. The term also refers to the hypothesis that posits the existence of this stage. Alexander Rich first proposed the concept of the RNA world in 1962, and Walter Gilbert coined the term in 1986. Alternative chemical paths to life have been proposed, and RNA-based life may not have been the first life to exist. Even so, the evidence for an RNA world is strong enough that the hypothesis has gained wide acceptance. The concurrent formation of all four RNA building blocks further strengthened the hypothesis. Regardless of its plausibility in a prebiotic scenario, the RNA world can serve as a model system for studying the origin of life. Like DNA, RNA can store and replicate genetic information; like protein enzymes, RNA enzymes ( ribozymes) can catalyze (start or accelerate) chemical reactions that ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
