Presentation on theme: "The Myth of the Dinosaurs’ Broken DNA 恐龍基因破碎之謎 (B4)"— Presentation transcript:
1The Myth of the Dinosaurs’ Broken DNA 恐龍基因破碎之謎 (B4) Hong Kong Student Science Project Competition 2004The Myth of the Dinosaurs’ Broken DNA 恐龍基因破碎之謎 (B4)Diocesan Girls’ SchoolTracy Law, Sindy Wong, Polly Yu, Queenie Lai
2Observation Advanced biotechnology and cloning technology There are no dinosaurs clonedDNA molecules of dinosaurs are brokenOxidation may be a major cause in breaking down the DNA moleculesOxidation of DNA molecules can be brought about by oxidizing agents and free radicals
3ProblemWhy was the dinosaur DNA broken into fragments as found in the fossils?
4HypothesisFree radicals have a stronger action on DNA molecules than oxidizing agents.
5AimTo compare the effectiveness of free radicals and oxidizing agents in breaking down the DNA molecules.
6Principles Breaking Down of DNA DNA is a giant chain of nucleotides Nucleotides are linked together by phospho-ester bondsBreaking down of DNA is due to the destruction of phospho-ester bonds of the sugar-phosphate backbone of the molecules
7We use DNA from pig liver because of the following reasons: Source of DNAWe use DNA from pig liverbecause of the following reasons:Liver cells have relatively bigger nuclei, it would be easier to extract DNADNA molecules are all similar in structurePig liver is easily available
8Source of Free Radicals Free radicals will be formed from hydrogen peroxide in the presence of iron (III) ions.Fe 2+ + H2O2 ----> Fe 3+ + OH OH Fe 3+ + H2O2 ----> Fe OOH + H+We propose that these free radicals react with and break the DNA chainsSource of Oxidizing AgentsHydrogen peroxide and acidified potassium permanganate are used in this experiment because they are well-known oxidizing agents.
9DNA Gel Electrophoresis PolesThe negatively charged DNA molecules will move to the anode side of the gelGelAnodeCathodeGelContains pores so that DNA molecules can pass throughThe negatively charged DNA molecules will move to the anode side of the gel
10Setup Reactants Design of the experiment A Pure pig liver DNA B DNA+ 6% H2O2CDNA M KMnO4/H+DDNA M FeCl3EDNA + 6% H2O M FeCl3
11Independent variable: Various treatments of DNADependent variable:The DNA pattern on the gelControl variables:Time of running the gel, source of DNA extracts (pig), temperature, pH
12AssumptionIf pig’s DNA is broken down by the attack of free radicals, dinosaurs' DNA can be broken down by the same mechanism.
13Procedures Preparation of DNA samples Cut pig liver tissue into smaller piecesPurify DNA by adding chemicals and enzymes, followed by centrifugation
14DNA gel electrophoresis Add TE buffer into the gel tankLoad DNA samples into the wellsConnect the gel tank to a150V power pack
15Stain the gel overnight using methylene blue Visualization of DNAStain the gel overnight using methylene blueDestain the gel in distilled water
17FindingsThe oxidizing power of hydrogen peroxide and acidified potassium permanganate is not strong enough to break the DNA strandsFerric chloride forms crypto-hydroxyl radicals with DNA molecules, and the mechanism causes DNA to break into smaller pieces
18Ferric chloride and hydrogen peroxide react with each other to form hydroxyl radicals, which then react with DNA molecules and break them down into smaller piecesFree radicals have a stronger breaking action on DNA molecules
19ConclusionFree radicals were a more likely cause for breaking down the dinosaurs’ DNA than oxidizing agents.