How ERVs work and how they show common ancestry

1. How ERVs work and how they show common ancestry Time 2008-05-29 18:42
ERV counter-arguments are refuted in the videos I set as responses to this one.VIDEO TRANSCRIPT:The following is an animation, produced by the Boehringer Ingelheim Corporation, explains how endogenous retroviruses work. The example being used is human immunodeficiency virus. I also added commentary of my own, that explains how ERVs show that we evolved from the same ancestor that Chimpanzees did. Step one is the infection of a suitable host-cell, such as a CD4+ (cluster of differentiation 4) T lymphocyte. Entry of HIV (human immunodeficiency virus) into the cell requires the presents of certain receptors on the cell's surface: CD4 receptors and co-receptors such as CCR5 (Chemokine (C-C motif) receptor 5) or CXCR4 (Chemokine (C-X-C motif) receptor 4). These receptors interact with protein complexes, which are embedded in the viral envelope. These complexes are comprised of two glycoproteins: an extra-cellular GP120 and a trans-membrane GP41. When HIV approaches a target cell, GP120 binds to the CD4 receptors. This process is termed "attachment". It promotes further binding to a co-receptor. Co-receptor binding results in a conformational change in GP120. This allows GP41 to unfold and insert its hydrophobic terminus into the cell membrane. GP41 then folds back on itself. This draws the virus towards the cell and facilitates the fusion of their membranes. The viral nucleocapsid enters the host-cell and breaks open, releasing two viral RNA strands, and three essential replication enzymes: integrase, protease, and reverse transcriptase. Reverse transcriptase then begins the reverse transcription of viral RNA. It has two catalytic domains: the ribonuclease H active site and the polymerase active site. Here, single stranded, viral RNA is transcribed into an RNA/DNA double-helix. Ribonuclease H breaks down the RNA. The polymerase then completes the remaining DNA strand to form a DNA double-helix. Now, integrase goes into action. It cleaves a dinucleotide from each 3-prime end of the DNA, creating two "sticky" ends. Integrase then transfers the DNA into the cell nucleolus and facilitates its integration into the host-cell genome. The host-cell genome now contains the genetic information of HIV. Activation of the cell then induces transcription of pro-viral DNA into messenger RNA. If the virus does activate, the immediate production of thousands retroviral copies quickly overwhelms, and kills the cell. If, however, the virus fails to activate, it will become a permanent fixture within the genome and the cell will not be compromised by this process of replication and will continue functioning normally. Now, if this cell happens to be a reproductive cell that is part of a sperm or an egg, and that sperm or egg happens to be used to produce an offspring, that retroviral code will be part of the offspring's genome. Since that particular retroviral marker in that particular section of the genome is only transmissible by sexual reproduction, if two beings share a marker, you can be sure they share a common ancestor as well. If the two beings are of the same species, that common ancestor may be as well. But if they are of different species, there must have been a time when those two species were one, and the common ancestor passed on the retroviral code before the split occurred. Since Humans and Chimpanzees share retroviral markers, we can be sure that both share a common ancestor. For educational purposes, here's what happens if things go as they normally do, and the virus activates:The viral messenger RNA migrates into the cytoplasm, where building blocks for a new virus are synthesized. Some of them have to be processed by the viral protease. Protease cleaves longer proteins into smaller core proteins. This step is crucial to create an infectious virus. Two viral RNA strands and the replication enzymes then come together and core proteins assemble around them, forming the capsid. This immature viral particle leaves the cell, acquiring a new envelope of host and viral proteins. The virus matures and becomes ready to infect other cells. HIV replicates billons of times per day, destroying the host's immune cells and eventually causing disease progression.Graphical Representations:Reverse transcriptase http://www.cs.stedwards.edu/chem/Chem...Polymerasehttp://www-bioc.rice.edu/~siyang/poly...Ribonuclease Hhttp://upload.wikimedia.org/wikipedia...Integrasehttp://www-mslmb.niddk.nih.gov/thang/...Proteasehttp://www.whozoo.org/mac/Music/3Dima...
Tag: »AIDS »DNA »Darwin »ERV »HIV »ancestry »cancer »common »decent »endogenous »evolution »genetics »how »junk »non-coding »retrovirus »work
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