Ashley SefretMarch 26, 2013BSCI105 Notes for Exam 3PHOTOSYNTHESIS- Two major components: reactions that require light and those that don’t require light (Calvin Cycle)- Things that go thru respiration: plants, multicellular algae, unicellular protists, individual bacteria (like purple sulfur), cyanobacteriaFrom leaves to chloroplasts: - Leaves have veins, in cross sections there are chloroplasts, stomata are pores on suface of leaf that allow CO2 to go in and O2 to go out (when its dark and cool they open, and they close when it gets warmer to conserve water in plant)- Chloroplasts have double layer (like mitochondria), stack of thylakoid disk is called a granumOverview of Photosynthesis DIAGRAM 1carbon dioxide is reduced and sugar is the productlight reactions are reduced to NADPH and get oxidized in Calvin CycleTracking Reactants in Labeling Experiments: DIAGRAM 2Carbons and Oxygen of CO2 become part of glucosePhotosystems Harvest Light and Act as Redox Systems:- 1: Photon (light energy) is absorbed by a pigment, electron gets excited, and the energy gets passed down to diff pigments and ultimately to a pair of chlorophyll a molecules which then pass it to election then onto the reaction center complex One side of the photosystem in in contact with stroma and one in touch with thylakoid center- 2: - interaction between 2 photosystems DIAGRAM 3The Light Reactions of Photosynthesis: Linear Electron Flow in PSII and PSIJust follow the light and the electronsLight Reactoins Happen in Thylakoid Membrane – go thru electron transport chains and make ATP and NADPH to go into Calvin CycleLook at Steps in Liner Electron Flow SlideCarbohydrates are Synthesized in the Calvin Cycle (light independent) in Stroma- 3 CO2 enters at a time, - Phase 1: carbon fixation – 6 ATP will go in to make 6 ADP, the 6 NADPH go in to make 6 NADP+ and 6 Pi- phase 2: Reduction – a 3 phosphate sugar makes G3P output (Sucrose – can be used for metabolism or stored as starch)- Phase 3: 3/28/13The Molecular Basis of Inheritance – how it was figured out that DNA is genetic molecule*****The Big Picture*****:- Genetic studies from the early 20th century identified chromosomes as the basis for inheritance- Chromosomes consist of chromatin, which contains both protein and DNA – but the challenge was to identify which component was the actual genetic material- Work with bacteria and their viruses “bacteriophages”, indicated that DNA and not protein contained the genetic information- Solving the structure of DNA provided an intuitive mechanism for how DNA can be replicated, thus also providing a mechanism for inheritanceGenetic Material- Genes are located on chromosomes (T.H. Morgan study on fruit flies)- Chromosomes consist of chromatin, but what is genetic material… the DNA or Protein?o Early hypothesis chose protein bc 20 amino acids seemed better for storing info than just 4 bases of DNAo But…. its DNA- Fruit flies were still to complicated to figure this outThe Griffith Experiment- Griffith worked with 2 strains of pneumococcus (bacteria): 1 strain S was smooth and caused lethal diseas in mice; rough R strain which is harmless- Injecting both strings together (killed S strain and live R) resulted in lethal disease, and live Sstrain bacteria could be recovered from the mice- Conclusion: some of the R strain was transformed into live S strain by picking up a component from the killed/dead S strainWhat is the Transforming Agent?- Follow up experiment that broke open each bacteria (lysed) and treated with agents that destroyed either protein RNA or DNA- The remaining lysates were then mixed with R strain bacteria to look for the transformation into S strain- Result (14 yrs later): if you destroyed DNA, then the transformation didn’t happen…SO DNA represents the genetic material- There were still skepticisms about DNA so more experiments were conducted using bacterialviruses called bacteriophages (or phages), which is basically just all protein and DNA..so one of them must represent phages genetic material – Hershey-Chase ExperimentHershey Chase Experiment- T2 phage genetic material would have to get inside of E. coli cell- So they separately labeled some phage with the radioactive isotopes 35S (proteins) and 32p (DNA)- Radioactive phages were allowed to infect E. Coli briefly and then any phage remnants still outside of the bacteria were separated from the bacterial cells- Look for radioactivity in either bacterial cells OR in the culture liquid- Results : o radioactive DNA was found in bacteria, o And the radioactive proteins were found in the culture liquid, but not bacteriao NOW, both bacteria and the phages that infect bacteria use DNA as genetic materialChargaff’s Rules:- Studied biochemical makeup of DNA in different species- Previously thought that DNA composition was essentially the same, but he showed that they vary from species to species- Also found that proportion of A and T is about equal and same with the proportion of G andC- Foreshadowed the double-helix structure of DNAThe Race to DNA Structure:- Rosalind Franklin was using X-Ray Diffraction (crystal form bends light) to determine the structure of DNA- James Watson saw one of her structures and realized that it implied a helical structure- Also saw that the bases were on the inside of the helix and the sugar-phosphate backbones were on the outside- SO, Francis Crick and Watson constructed models that could explain the X-ray diffraction paddle DNA- Sugar (deoxyribose) – phosphate chain, nitrogenous bases A,T,C,G- One end of DNA is the 5’ end (left) and the other is the 3’ end (right)- Information is read in the cell from the 5’ end 3’ end- Bases form hydrogen bonds with each other: 3 between C and G; 2 between T and A- Double helix – 2 separate strands of DNA- Antiparallel, going in opposite directions- Bases on inside and sugar-phosphate on outside (hydrophilic)- A with T, C with G (Chargaff’s rule of proportions)- Base pairing implies complementarity: the base identity on one strand automatically determines the base identity of the other strand (mechanism for DNA replication) – info on 1 strand indicates the info (sequence of bases) on the other strand- Information from DNA is eventually transferred to proteins4/2/13THE BIG PICTURE- DNA replication generates 2 identical “daughter” molecules in a semi-conservative (one old and one new strand) mechanism- Replication of a chromosome begins at one or
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