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Table of contents

Analysis of the giant Mimivirus may support this hypothesis. This virus contains a relatively large repertoire of putative genes associated with translation — genes that may be remnants of a previously complete translation system. Interestingly, Mimivirus does not differ appreciably from parasitic bacteria, such as Rickettsia prowazekii Raoult et al. Figure 4 The progressive and regressive hypotheses both assume that cells existed before viruses.

What if viruses existed first? Recently, several investigators proposed that viruses may have been the first replicating entities. Koonin and Martin postulated that viruses existed in a precellular world as self-replicating units. Over time these units, they argue, became more organized and more complex. Eventually, enzymes for the synthesis of membranes and cell walls evolved, resulting in the formation of cells.

Viruses, then, may have existed before bacteria, archaea , or eukaryotes Figure 4; Prangishvili et al. We also know that some RNA molecules, ribozymes, exhibit enzymatic properties; they can catalyze chemical reactions. Perhaps, simple replicating RNA molecules, existing before the first cell formed, developed the ability to infect the first cells.

Villarreal and DeFilippis and Bell described models explaining this proposal. Perhaps, both groups postulate, the current nucleus in eukaryotic cells arose from an endosymbiotic-like event in which a complex, enveloped DNA virus became a permanent resident of an emerging eukaryotic cell. Where viruses came from is not a simple question to answer. One can argue quite convincingly that certain viruses, such as the retroviruses, arose through a progressive process.

Mobile genetic elements gained the ability to travel between cells, becoming infectious agents. One can also argue that large DNA viruses arose through a regressive process whereby once-independent entities lost key genes over time and adopted a parasitic replication strategy.

Where did viruses come from? - Scientific American

Finally, the idea that viruses gave rise to life as we know it presents very intriguing possibilities. Perhaps today's viruses arose multiple times, via multiple mechanisms. Perhaps all viruses arose via a mechanism yet to be uncovered. Today's basic research in fields like microbiology, genomics , and structural biology may provide us with answers to this basic question.

Contemplating the origins of life fascinates both scientists and the general public.

New study transforms understanding of virus origins and evolution

Understanding the evolutionary history of viruses may shed some light on this interesting topic. To date, no clear explanation for the origin s of viruses exists. Viruses may have arisen from mobile genetic elements that gained the ability to move between cells. They may be descendants of previously free-living organisms that adapted a parasitic replication strategy.

Perhaps viruses existed before, and led to the evolution of, cellular life. Continuing studies may provide us with clearer answers. Or future studies may reveal that the answer is even murkier than it now appears. Andersson, S. The genome sequence of Rickettsia prowazekii and the origin of mitochondria. Nature , — doi Bell, P. Viral eukaryogenesis: Was the ancestor of the nucleus a complex DNA virus? Journal of Molecular Evolution 53 , — doi Koonin, E. On the origin of genomes and cells within inorganic compartments.

Trends in Genetics 21 , — Lander, E. Initial sequencing and analysis of the human genome.

La Scola, B. A giant virus in Amoebae. Science , doi Nelson, M. The evolution of epidemic influenza. Prangishvili, D. Viruses of the Archaea: A unifying view. Nature Reviews Microbiology 4 , — doi Raoult, D. Redefining viruses: Lessons from mimivirus.

Nature Reviews Microbiology 6 , — doi The 1. Science , — doi Villarreal, L. A hypothesis for DNA viruses as the origin of eukaryotic replication proteins. Journal of Virology 74 , — Xiao, C.

References

Cryo-electron microscopy of the giant Mimivirus. Journal of Molecular Biology , — doi What Is a Cell? Eukaryotic Cells. Cell Energy and Cell Functions. Photosynthetic Cells. Cell Metabolism. The Origin of Mitochondria. Mitochondrial Fusion and Division. The Origin of Plastids. The Origins of Viruses. Discovery of the Giant Mimivirus. Volvox, Chlamydomonas, and the Evolution of Multicellularity. Yeast Fermentation and the Making of Beer and Wine.

What Happens When Viruses Evolve?

Dynamic Adaptation of Nutrient Utilization in Humans. Nutrient Utilization in Humans: Metabolism Pathways. An Evolutionary Perspective on Amino Acids. Mitochondria and the Immune Response. Stem Cells in Plants and Animals. Promising Biofuel Resources: Lignocellulose and Algae. The Discovery of Lysosomes and Autophagy. The Mystery of Vitamin C.

Viruses, Origin and Evolution, Quasispecies, Smart Resistance

Wessner, Ph. How did viruses evolve? Are they a streamlined form of something that existed long ago, or an ultimate culmination of smaller genetic elements joined together? Aa Aa Aa. The Basics of Viruses. Are Viruses Alive? Figure 1. Where Did Viruses Come From?