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Facts Of Evolution: Retroviruses And Pseudogenes ... Facts of Evolution (Chapter 9): Retroviruses And Pseudogenes. --- Please SUBSCRIBE to Science & Reason: • • • --- EVOLUTION IS REAL SCIENCE: 1. Does The Evidence Support Evolution? 2. Vitamin C And Common Ancestry 3. Are We Descended From Viruses? 4. Does The Fossil Record Support Evolution? 5. Where Are The Transitional Forms? FACTS OF EVOLUTION: 1. Introduction 2. Universal Common Descent 3. Good Design, Bad Design 4. Speciation And Extinction 5. How Fast Is Evolution? 6. What Can Embryos Tell Us About Evolution? 7. The Molecules Of Life 8. Molecular Evolution: Genes And Proteins 9. Retroviruses And Pseudogenes --- RETROVIRUSES A retrovirus is an RNA virus that is replicated in a host cell via the enzyme reverse transcriptase to produce DNA from its RNA genome. The DNA is then incorporated into the host's genome by an integrase enzyme. The virus thereafter replicates as part of the host cell's DNA. Retroviruses are enveloped viruses that belong to the viral family Retroviridae. The virus itself stores its nucleic acid in the form of a +mRNA (including the 5'cap and 3'PolyA inside the virion) genome and serves as a means of delivery of that genome into cells it targets as an obligate parasite, and constitutes the infection. Once in the host's cell, the RNA strands undergo reverse transcription in the cytosol and are integrated into the host's genome, at which point the retroviral DNA is referred to as a provirus. It is difficult to detect the virus until it has infected the host. Simply, the retrovirus enters a host cell and provokes the RNA strands inside of the normally-functioning cell to undergo reverse transcription. Normally, DNA would be transcribed into RNA, and RNA would translate into proteins. However, when a retrovirus is inside of a cell, the first two steps of that process would be switched. (Rather than DNA -- RNA -- Protein, it would be RNA -- DNA) The host cell would become a provirus as this has occurred. • --- PSEUDOGENES Pseudogenes are defunct relatives of known genes that have lost their protein-coding ability or are otherwise no longer expressed in the cell. Although some do not have introns or promoters (these pseudogenes are copied from mRNA and incorporated into the chromosome and are called processed pseudogenes), most have some gene-like features (such as promoters, CpG islands, and splice sites), they are nonetheless considered nonfunctional, due to their lack of protein-coding ability resulting from various genetic disablements (stop codons, frameshifts, or a lack of transcription) or their inability to encode RNA (such as with rRNA pseudogenes). Thus the term, coined in 1977 by Jacq, et al., is composed of the prefix pseudo, which means false, and the root gene, which is the central unit of molecular genetics. Because pseudogenes are generally thought of as the last stop for genomic material that is to be removed from the genome, they are often labeled as junk DNA. Nonetheless, pseudogenes contain fascinating biological and evolutionary histories within their sequences. This is due to a pseudogene's shared ancestry with a functional gene: in the same way that Darwin thought of two species as possibly having a shared common ancestry followed by millions of years of evolutionary divergence (see speciation), a pseudogene and its associated functional gene also share a common ancestor and have diverged as separate genetic entities over millions of years. •
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