2 Early Earth Earth is about 4.6 billion years old Fossils resembling photosynthetic prokaryotes have been found in dome shaped rocks called stromatolites, date back to 3.5 billion year ago.
3 Origin of Organic Molecules In 1953, Miller & Urey designed an experiment to simulate conditions on early EarthUnder many different conditions this basic set up has produced all 20 amino acids, several sugars, lipids, the nitrogenous bases found in DNA & RNA and ATPSolutions of amino acids and dropped them onto the surface of hot sand, clay or rocks has resulted in the formation of polypeptides
4 The RNA WorldA characteristic of life is the process of inheritance, which is based on molecules that can copy themselves.DNA RNA ProteinHow did this information flow originate?A popular hypothesis is that genes were originally short strands of RNA capable of replicating without enzymesScientists have observed RNA molecules copying themselves in solutions containing nucleotides without enzymes or cells presentDuring the “RNA world”, RNA might have stored genetic information in addition to directing protein synthesis
5 Formation of Pre-Cells Experiments have shown that polypeptides can form microscopic fluid-filled spheres.If certain kinds of lipids are in the solution selectively permeable membranes will form.These “molecular packages” are referred to as pre-cells
6 Hypothetical 4-Stage Sequence for Origin of Life Small organic molecules formed from simpler inorganic moleculesThese small molecules joined into more complex onesMolecules that could copy themselves provided a basis for inheritance of molecular informationThese molecules became packaged within membranes and separated from their surroundings
7 Archaea v. Bacteria“archaea” is derived from the Greek work for ancientExist in harsh habitats resembling conditions of early EarthThey are referred to as “Extremophiles”ThermophilesHalophilesanaerobicBelieved to be as closely related to eukaryotes as they are to bacteriaContain different information in their nucleic acidsRNA polymerases differLack intronsSusceptible to antibiotics that do not affect archaeaContain peptidoglycan in their cell walls
9 Structure & Function of Bacteria: Shape Cocci – sphericalBacilli – rod-shapedSpirilla – spiral shaped
10 Structure & Function of Bacteria: Cell Wall Gram + (purple stain): thick layer of peptidoglycanGram – (pink stain): thinner layer of peptidglycan with outer membrane
11 Structure & Function of Bacteria: Motility FlagellumPilliSlime secretion
12 Bacterial Reproduction Binary fission: DNA is copied and moved to opposite ends of the cell as the cell divides; occurs almost continuously.Rapid reproduction rate, many can divide within 20 minuteResults in a colony of cells that are clones (unless mutations occur)
13 Genetic VariationDespite reproducing asexually, bacteria are able to obtain genetic variation through conjugationTwo bacterial cells temporarily join and exchange plasmid DNA; does not need to occur between cells of the same species/strain
14 EndosporesAllow bacteria to survive periods of very harsh conditions by going into a dormant endospore formAfter copying DNA, one copy is surrounded by a thick protective coat and the outer cell disintegratesOften able to survive for years in this state, when conditions are more favorable, the endospores will absorb water and grow again.
16 The Oxygen RevolutionThe evolution of photosynthetic cyanobacteria resulted in the presence of free oxygen in oceans, lakes & the atmosphereThis oxygen was toxic to many existing organisms because it attacks the bonds of organic molecules & many went extinctSome were not exposed to oxygen and remained anaerobic; their descendants still exist in similar environments todayA small number were able to use the oxygen in the extraction of energy from food, their descendents are the wide variety of aerobic organisms in existence today
17 Beneficial Uses of Bacteria Chemical recycling:Decomposers: replenish soil nutrients and release CO2 back to the atmosphereNitrogen fixing bacteria: convert nitrogen gas in the atmosphere to an organic form usable by other organisms for nucleotide and amino acid formationBioremediation:Sewage treatment: decompose organic matter in sewage sludgeOil spill clean-up: genetically modified digest oilClean old mining sites: detoxify by extracting lead & mercuryMedicine/Pharmaceuticals:Produce desired gene products: insulin, HGHProbiotics: restore beneficical intestinal bacteriaFood:CheeseYogurt
18 Viruses & Bacteriophage: The Boundary of LifeAll living things share 8 characteristics. Viruses do not meet all of these characteristics.Viruses attack eukaryotic cells and Bacteriophages attack prokaryotic cells.Viruses and phages are capable of reproducing at a very rapid rate, but only in a host cell.Viruses are responsible for many diseases and can be found everywhere.
20 Viruses & DiseaseMethod of causing disease is very different from that of bacteriaTherefore methods for treatment & prevention differ from methods for bacteriaAntibiotics will not work on viruses because they target specific not found in viruses or host cellsDamage or prevent formation of bacterial cell wallSome examples of viral diseases include:Influenza (RNA) Polio (RNA)Common cold (RNA) Hepatitis (DNA)Measles (RNA) Herpes (DNA)Mumps (RNA) Smallpox (DNA)AIDS (RNA) Rabies (RNA)
21 Viral InfectionViruses and bacteriophages invade cells and use the host cell's machinery to synthesize more of their own macromolecules.Once inside the host the bacteriophage or virus may go into two reproductive cycles:Lytic cycle: destroying the host cell during reproduction.Lysogenic Cycle – a parasitic type of partnership with the cell
23 Viruses are host specific – a protein on the surface of the virus has a shape that matches a molecule in the plasma membrane of its host, allowing the virus to lock onto the host cell.
24 ProvirusesA provirus is a DNA virus that has been inserted into a host cell chromosome.
25 Retroviruses & HIVRetroviruses reverse the normal DNA to RNA to protein flowIn RNA viruses, the RNA nucleotide will be translatedReverse transcriptase catalyzes the synthesis of DNA from an RNA template, the DNA intermingles with host DNA as a provirus making it difficult to detect
26 PrionsProteins that cause several diseases of the brain: Mad cow disease, Kuro, Creutzfeldt-Jacob disease (CJD) & Scrapie (in sheep)Only infectious agent that do not contain genetic materialNormal form play important roles in brain function such as helping nerve cells communicateAbnormal prions destroy the brainThree ways to acquire abnormal prions:Infection with abnormal prionsInherited genes that give rise to abnormal prionsSpontaneous genetic mutations that give rise to abnormal prions
27 Viroids Small strands of RNA rather than strands of protein. Smaller than the strands of genetic info in viruses and contain no protein coat.Replicated using host cell machinery, like virusesCause plant diseases: potato spindle tuber, avocado sunblotch, chrysanthemum stunt, and chrysanthemum chlorotic mottle
30 HIV doesn’t target just any cell, it goes right for the cells that want to kill it. “Helper" T cells are HIV's primary target. These cells help direct the immune system's response to various pathogens.HIV undermines the body's ability to protect against disease by depleting T cells thus destroying the immune system. The virus can infect 10 billion cells a day, yet only about 1.8 billion can be replaced daily.
32 From HIV to AIDSDuring first few years (7-10) after HIV infection, person is usually asymptomatic.During the symptomatic phase, the body has insufficient numbers of T-Cells (from normal /mm3 to 200/ mm3 ) to mount an immune response against infections.Chronic diarrhea, minor mouth infections, night sweats, headache & fatigue are commonAt the point when the body is unable to fight off infections, a person is said to have the disease AIDS. (Generally when count drops below 200 /mm3 )It is not the virus or the disease that ultimately kills a person; it is the inability to fight off something as minor as the common cold.
33 AIDS: The Global Epidemic Around 2.6 million people became infected with HIV in 2009.Sub-Saharan Africa has been the hardest hit by the epidemic. In 2009 over two-thirds of AIDS deaths were in this region