Presentation on theme: "The Myth of the Dinosaurs’ Broken DNA 恐龍基因破碎之謎 (B4) Diocesan Girls’ School Tracy Law, Sindy Wong, Polly Yu, Queenie Lai Hong Kong Student Science Project."— Presentation transcript:
The Myth of the Dinosaurs’ Broken DNA 恐龍基因破碎之謎 (B4) Diocesan Girls’ School Tracy Law, Sindy Wong, Polly Yu, Queenie Lai Hong Kong Student Science Project Competition 2004
Observation Advanced biotechnology and cloning technology There are no dinosaurs cloned DNA molecules of dinosaurs are broken Oxidation may be a major cause in breaking down the DNA molecules Oxidation of DNA molecules can be brought about by oxidizing agents and free radicals
Problem Why was the dinosaur DNA broken into fragments as found in the fossils?
Hypothesis Free radicals have a stronger action on DNA molecules than oxidizing agents.
Aim To compare the effectiveness of free radicals and oxidizing agents in breaking down the DNA molecules.
Principles Breaking Down of DNA Nucleotides are linked together by phospho-ester bonds Breaking down of DNA is due to the destruction of phospho-ester bonds of the sugar-phosphate backbone of the molecules DNA is a giant chain of nucleotides
Source of DNA We use DNA from pig liver because of the following reasons: Liver cells have relatively bigger nuclei, it would be easier to extract DNA DNA molecules are all similar in structure Pig liver is easily available
Free radicals will be formed from hydrogen peroxide in the presence of iron (III) ions. Fe 2+ + H 2 O > Fe 3+ + OH - +. OH Fe 3+ + H 2 O > Fe OOH + H + We propose that these free radicals react with and break the DNA chains Source of Free Radicals Source of Oxidizing Agents Hydrogen peroxide and acidified potassium permanganate are used in this experiment because they are well-known oxidizing agents.
DNA Gel Electrophoresis Poles The negatively charged DNA molecules will move to the anode side of the gel Gel Anode Cathode Gel Contains pores so that DNA molecules can pass through The negatively charged DNA molecules will move to the anode side of the gel
Design of the experiment SetupReactants APure pig liver DNA BDNA+ 6% H 2 O 2 CDNA M KMnO 4 /H + DDNA M FeCl 3 E DNA + 6% H 2 O M FeCl 3
Independent variable: Various treatments of DNA Dependent variable: The DNA pattern on the gel Control variables: Time of running the gel, source of DNA extracts (pig), temperature, pH
Assumption If pig’s DNA is broken down by the attack of free radicals, dinosaurs' DNA can be broken down by the same mechanism.
Procedures Preparation of DNA samples Cut pig liver tissue into smaller pieces Purify DNA by adding chemicals and enzymes, followed by centrifugation
Add TE buffer into the gel tank Load DNA samples into the wells Connect the gel tank to a 150V power pack DNA gel electrophoresis
Visualization of DNA Stain the gel overnight using methylene blue Destain the gel in distilled water
Front Setup ASetup CSetup E Setup BSetup D Bulges Result Bulges
Findings Ferric chloride forms crypto-hydroxyl radicals with DNA molecules, and the mechanism causes DNA to break into smaller pieces The oxidizing power of hydrogen peroxide and acidified potassium permanganate is not strong enough to break the DNA strands
Free radicals have a stronger breaking action on DNA molecules Ferric chloride and hydrogen peroxide react with each other to form hydroxyl radicals, which then react with DNA molecules and break them down into smaller pieces
Conclusion Free radicals were a more likely cause for breaking down the dinosaurs’ DNA than oxidizing agents.