Presentation on theme: "ORIGINAL QUESTION: Which molecule contains genetic information?"— Presentation transcript:
ORIGINAL QUESTION: Which molecule contains genetic information?
Experiments Frederick Griffith (1928) - English A. Smooth bacteria mouse = dies of pneumonia B. Rough bacteria mouse = lives C. Heat-killed smooth bacteria mouse = lives D. Heat-killed smooth bacteria + mouse = dies of pneumonia Live rough bacteria
Fig. 12.2p. 327
Griffith Conclusion: Some molecules changed the harmless rough bacteria into deadly smooth bacteria transformation!
Oswald Avery (1944) - Canadian Question: What molecule was needed for transformation? Avery examined 4 macromolecules – destroying 1 at a time 1. Lipids3. Proteins 2. Carbohydrates4. Nucleic Acids (DNA)
Transformation was blocked ONLY when DNA was destroyed Conclusion = Genes are made of DNA
Alfred Hershey & Martha Chase (1952) - American Bacteriophage = a virus that infects bacteria Made of protein and DNA Question: Which enters a bacterium during infection? They used tracers = radioactive isotopes 1.phosphorus-32 part of DNA (not proteins) 2.sulfur-35 part of proteins (not DNA)
Question: Which enters a bacterium during infection? They used tracers = radioactive isotopes 1. phosphorus-32 part of DNA (not proteins) 2. sulfur-35 part of proteins (not DNA)
Hershey & Chase Procedure: A) Let bateriophages infect bacteria B) Analyzed bacteria for radioactivity C) Found phosphorus-32 sample made the bacteria radioactive Conclusion: Genetic material is DNA NOT protein
Martha Chase & Alfred Hershey
Nucleic acids = chain of nucleotides (polymer) Nucleotides consist of : 1.5-carbon sugar 2.phosphate group 3.nitrogenous base
Nucleotides Fig. 12.4
DNA: deoxyribonucleic acid is a nucleic acid Made of 4 different nucleotides: 1.adenine3.guanine 2.cytosine4.thymine
Chargaffs Rules - Erwin Chargaff (1950) - American In samples of DNA: The amounts of adenine (A) and thymine (T) were equal The amounts of cytosine (C) and guanine (G) were equal Chargaffs Rule: C = G and T = A
Rosalind Franklin & Maurice Wilkins (1952) – British Used X-Ray diffraction to analyze DNA molecules These X-Ray patterns helped to solve the structure of DNA
James Watson & Francis Crick (1953) – American & English Solved the mystery! DNA is made of 2 strands twisted in adouble helix Base pairs are formed between nitrogenous bases (A, T, C, G) Hydrogen bonds formed between A and T Hydrogen bonds formed between C and G
Frances Crick James Watson
Watson & Crick Kind of like a twisted ladder! Rails of the ladder are strands of alternating deoxyribose and phophate One rail runs up, the other runs down The steps or rungs are the pairs of bases (C-G or T-A)
DNA Structure : Fig. 12.8
Nucleosomes Tiny particles that help to fold and package DNA so it can fit inside the nucleus If all of the DNA in one human cell were laid out end to end, it would be almost 2 meters long!
Nucleosomes : Fig. 12.9
QUESTION: How does DNA replicate?
Semiconservative Replication 1. Enzymes separate the 2 strands 2. New strands are synthesized 3. This occurs during the S phase of the cell cycle
Why must DNA be replicated? When a cell divides, each new cell needs a copy of the genetic material
Semiconservative Replication A DNA strand that looks like… A T A G C G C A T T A C T A T C G C G T A A T G
…can be untwisted, broken apart, and have new nucleotides paired with BOTH of the original sides, forming 2 new strands. After the DNA strand is replicated it will look like this: A T A G C G C A T T A C T A T C G C G T A A T G A T A G C G C A T T A C T A T C G C G T A A T G