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Lecture

Biology 1001 UWO Outcomes

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Department
Biology
Course
Biology 1001A
Professor
Paul Ragogna
Semester
Fall

Description
September 12 2012Evolution in Action Human Immunodeficiency Virus HIVGeneral global distribution of HIV infectionso Most prevalent in SubSahara AfricaGeneral temporal trends in HIV infection rateso The number of people living with HIV and the HIV caused deaths are still increasing despite the incredible amount of research that is being investedFactors that explain why no cure or universal vaccine has been developed for HIVAIDSo The disease mutates quickly and when scientists become close to a cure the disease changes too rapidly to keep upReasons why viruses are not considered aliveo For an organism to be considered alive it must be cellular in itself whereas a virus must inhabit a host cell in order to liveReasons why antiviral drug therapies often have serious side effectso They do not target the pathogen but rather inhibit its environment Major steps in life cycle of HIV 1Virion enters host cell 2Reverse Transcriptase viral DNA 3Integrase splices viral DNA into host DNA 4Transcription translation new virions assemble and bud offor lyse out 5Antiretroviral Therapies ARTs inhibit virus specific enzymes Specific role of integrase and reverse transcriptase in retroviral life cycleo Integrase enables its genetic material to be integrated into the DNA of the infected cellReverse transcriptase creates singlestranded DNA from an RNA templateMechanism of action of AZT o AZT works by selectively inhibiting HIVs reverse transcriptase the enzyme that the virus uses to make a DNA copy of its RNAReasons why effectiveness of AZT decreases over timeo HIV evolves and mutates creating resistant forms that prevent AZT from workingThe frequency of the resistant form will increase because the resistant form of the virus is capable of survival and reproductionRationale for multidrug drug cocktail approach to treating viral infectionso It is inevitable for viruses to become resistant to one drug but by creating a number of different ones the likelihood of the virus developing a resistance to each of them is much less likelyPrinciples of evolution of HIV o Variation heritability differential reproduction change in genotype of populationRole of CCR532 mutation in human resistance to HIV infection o Homozygous carriers of the mutation are resistant to HIV1 infection because the mutation prevents functional expression of the CCR5 chemokine receptor normally used by HIV1 to enter cellsGlobal distribution of CCR532 allele September 12 2012o Principally found in Europe and western AsiaLikely explanations of modern distribution of CCR532 allele o Selectively favoured in Europe after historical epidemicsLecture 3 OriginsIndependent Study OutcomesCharacteristics shared by all life o Small number of biological systems that straddle line between biotic and abiotic worldsBest example isa virusDisplay many properties of lifereproduceevolve over timeBased on its ability to infect cellsContain DNA and RNA but lack cellular machinery and metabolism to synthesize their own proteins o There are seven characteristics shared by all lifeformsDisplay orderall forms of life are arranged in a highly ordered manner with the cell being the fundamental unit of lifeHarness and Utilize Energyuse it to main highly ordered stateReproduce Respond to Stimulimake adjustments to their structure function and behaviour in response to their environmentExhibit Homeostasisregulate internal environmentGrowth and Developmentincrease their size by increasing the size of andor number of cells Evolvechange over generations to adapt to their surroundings In what way properties of life are emergent o They come about or emerge from many simpler interactions that in themselves do not have the properties found at higher levelsEx Ability to harness and utilize energy emerges from the interactions of the metabolic processCharacteristics of the habitable zone of a solar system o The region of space around a star where temperatures would allow for liquid watero The distance varies depending upon the type of star and how much energy it emitsConditions of a primitive Earth o All forms of life are composed of the major macromoleculesnucleic acids proteins lipids and carbohydrates With exception of lipids they are derived from simpler molecules such as nucleotides amino acids sugars o Primordial atmosphere contained abundance of water vapour large quantities of hydrogen carbon dioxide ammonia and methane o Most likely a reducing atmosphere todays is oxidizing o Molecules contained abundance of electrons and hydrogen and would have entered reactions with one another that yielded more complex organic molecules September 12 2012o OparinHaldane hypothesiswithout the ozone layer energetic ultraviolet light was able to reach the lower atmosphere and along with abundance of lightning provided energy needed to drive the formation of biologically important moleculesTypes of molecules that were and were not synthesized by the MillarUrey experiment o Components of reducing atmospherehydrogen methane ammonia and water vapourin a closed apparatus and exposed them to energy source of continuously sparking electrodes o Found a large assortment of organic compounds after a week includingurea amino acids and lactic formic and acetic acids after condensing the atmosphere into a liquid o Other chemicals have been tested in the apparatus including hydrogen cyanide HCN and formaldehyde CHO which were considered to be in primitive atmosphere 2o This produced building blocks of complex moleculesamino acids fatty acids the purine and pyrimidine components of nucleic acids sugars such as glyceraldehyde ribose glucose and fructose and phospholipids which form the lipid bilayers of biological membranes o Difficult environment for polymers to formnucleic acids are polymers of nucleotides and proteins are polymers of amino acidsClay surfaces catalyze polymerizationallows for short polymerization of proteins and nucleic acidsImportance of liposomes in evolution of first cells o Three key attributes of a modern cellMembranedefined compartmentthe cellA system to store genetic information and use it to guide the synthesis of specific proteinsEnergytransforming pathways to bring in energy form the surrounding and harness it to sustain life o Lipid sphere may have led to the development of cellsan early type of protobiont a group of abiotically produced organic molecules that are surrounded by a membrane or membranelike structure could have been similar to a liposome which is a lipid vesicle in which the lipid molecules form a bilayer very similar to a cell membrane Liposomes can easily be made in the laboratory and are selectively permeable only allowing some molecules to move in and outThe presence of clay not only catalyzes the polymerization of nucleic acids but also accelerates the formation of lipid vesiclesThis means lipid membrane system must have evolved with a genetic information system Characteristics of mimivirus that suggest it should be considered aliveCellularlike genesThe fact is can get sick makes it more aliveGenome harbouring more than 900 proteincoding genesCharacteristics of virophage
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