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UWL BIO 203 - Viruses
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Biology 203 1st Edition Lecture 6Outline of Last Lecture I. PhylogenyII. Using DNA sequences to create a phylogenetic treeIII. Molecular ClocksIV. FossilizationOutline of Current Lecture I. The Three Domains of LifeII. What are viruses?III. What do they do?IV. Do viruses exhibit the traits that unify earth’s living organisms?V. Where do they come from?VI. 2014-2015 Ebola OutbreakCurrent LectureI. The Three Domains of Lifea. All living things on earth have DNAb. All living things on earth produce cells with plasma membranesc. What are the characteristics of cellular life?i. Homeostasis – maintenance of statusii. Metabolism – transform energyiii. Heredity – DNA stores genetic information passed on to offspringiv. Evolution – changes in traits in response to mutation, drift, selection, etc.v. Behavior – respond to environmentvi. Reproduction – production of new individualsvii. Common Ancestry – all life on earth has a common ancestord. There are three domains of life:i. Bacteriaii. Archaeaiii. EukaryaII. What are viruses?a. Viruses are tiny; most are only visible using electron microscopyb. Genetic material (RNA or DNA) surrounded by a protein capsid (some also have a membrane)c. Viral particles are inert until they encounter a host cellThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.d. Morphology:i. Come in a wide variety of shapes and sizesii. Generally smaller than cellsiii. A few (pox viruses and pandoraviruses) are bigger than bacteria and even some eukaryotic cellsIII. What do viruses do?a. Viral particles enter host cells or inject genetic material into host cellsb. Use host cell’s “machinery” to replicate their genome and make new capsidsc. Enter by exocytosis or by bursting the host celld. The Rhinovirus (common cold)i. Optimized for performance at nose temperature (91-95 F)ii. Adheres to receptors on respiratory epithelial cells within 15 minutes of entering the bodyiii. Can survive up to 3 hours outside of a persone. Viruses are efficient parasites and have huge effects on individual organisms and even ecosystems (in both positive and negative ways)IV. Do viruses exhibit the traits that unify earth’s living organisms?a. NO homeostasisb. NO metabolismc. NO behaviord. NO common ancestryi. Small sets have a common ancestor, creating groupsii. Many viruses show more homology to the genes of their hosts than to the genesfrom other virusese. Some heredity, evolution and reproduction, but requires host cells and enzymesV. Where do viruses come from?a. Retroviruses appear to have evolved from “selfish DNA” called retrotransposons, which are present in many eukaryotes b. Retrotransposons are sections of DNA that can insert new copies of themselves within an organism’s genomec. Retrotransposons encode a gene that produces a reverse transcriptase (RT) proteind. The RT enzyme makes DNA copies of RNA transcribed from the retrotransposone. That DNA gets inserted somewhere else in the genomef. The “junk” DNA you may have heard of is partly retrotransposons!g. Retro-transposons pick up ‘extra’ DNA h. A few have an “envelope-like” gene. Some of these look like the capsid of viruses …i. Retroviruses (e.g., HIV, RSV) have a gene that includes the virus envelope proteinsj. Allow it to leave a cell, spread to adjacent cells (or organisms) and infect new cells!k. So, the huge array of retroviruses seems to have evolved from pre-existing retrotransposons in the genome of eukaryotes!l. Picornaviruses infect a diverse set of eukaryotesm. We know it is a single lineage because of molecular similaritiesn. Current evidence suggests these viruses radiated side by side with the EukaryotesVI. 2014 – 2015 Ebola Outbreaka. Difficult to study because only us and our close relatives are affectedb. Efforts to find treatments limited by our lack of baseline information, e.g. what animal serves as the reservoir?c. Biology:i. Part of the reason it is so deadly is that if affects front-line immune cells1. Macrophages – white blood cells which engulf foreign particles2. Dendritic cells – present antigens of pathogens to T cellsii. Infected cells release inflammation – causing molecules, resulting in clotting, hemorrhaging and tissue deathiii. No vaccine is available, but treating patients with antibodies harvested from recovering patients shows


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