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Do Now: 2.27

Do Now: 2.27. Objective: 1. Investigate famous experiments of the mid-20 th century that started the field of molecular genetics. Define transformation. Describe the “central dogma” of molecular genetics. Task: What experiment could you do to prove DNA in cells stores information?.

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Do Now: 2.27

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  1. Do Now: 2.27 Objective: 1. Investigate famous experiments of the mid-20th century that started the field of molecular genetics. Define transformation. Describe the “central dogma” of molecular genetics. Task: What experiment could you do to prove DNA in cells stores information?

  2. Scientists call this the: DNA DNA Central Dogma of Molecular Biology! RNA RNA Protein Protein

  3. How do we know that all of our genetic information comes from DNA? • What type of experiment would you design to determine that DNA is the source of all genetic information?

  4. Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation • Frederick Griffith was a bacteriologist studying pneumonia • He discovered two types of bacteria: • Smooth colonies • Rough colonies CONCLUSION: The smooth colonies must carry the disease!

  5. When heat was applied to the deadly smooth type… And injected into a mouse… The mouse lived! Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation

  6. Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation • Griffith injected the heat-killed type and the non-deadly rough type of bacteria. • The bacteria “transformed” itself from the heated non-deadly type to the deadly type.

  7. Griffith’s Experiment did not prove that DNA was responsible for transformation How would you design an experiment to prove that DNA was responsible for transformation?

  8. Avery, McCarty, and MacLeodRepeated Griffith’s Experiment Oswald Avery Maclyn McCarty Colin MacLeod

  9. Avery, McCarty, and MacLeodAdded the non-deadly Rough Type of Bacteria to the Heat-Killed Smooth Type and added enzymes that destroyed… Carbohydrates Lipids Proteins RNA DNA

  10. S-Type Carbohydrates Destroyed S-Type Lipids Destroyed S-Type Proteins Destroyed S-Type RNA Destroyed S-Type DNA Destroyed Conclusion: DNA was the transforming factor!

  11. The Hershey-Chase Experiment Protein coat Alfred Hershey & Martha Chase worked with a bacteriophage: A virus that invades bacteria. It consists of a DNA core and a protein coat DNA

  12. Protein coats of bacteriophages labeled with Sulfur-35 Phage • Hershey and Chase mixed the radioactively-labeled viruses with the bacteria Bacterium Phage The viruses infect the bacterial cells. Bacterium DNA of bacteriophages labeled with Phosphorus-32

  13. Protein coats of bacteriophages labeled with Sulfur-35 • Separated the viruses from the bacteria by agitating the virus-bacteria mixture in a blender DNA of bacteriophages labeled with Phosphorus-32

  14. Protein coats of bacteriophages labeled with Sulfur-35 • Centrifuged the mixture so that the bacteria would form a pellet at the bottom of the test tube • Measured the radioactivity in the pellet and in the liquid DNA of bacteriophages labeled with Phosphorus-32

  15. The Hershey-Chase results reinforced the Avery, McCarty, and MacLeod conclusion: DNA from viruses can cause change in other cells! However, there were still important details to uncover…

  16. How did DNA:1. Store information?2. Duplicate itself easily? These questions would be answered by discovering DNA’s structure

  17. The Race to Discover DNA’s Structure

  18. The Race to Discover DNA’s Structure 1940s Discovered the alpha-helical structure of proteins. Linus Pauling

  19. The Race to Discover DNA’s Structure Why do you think the bases match up this way? 1950 Chargaff’s Rule: Equal amounts of Adenine and Thymine, and equal amounts of Guanine and Cytosine Purine + Purine = Too wide Pyrimidine + Pyrimidine = Too Narrow Erwin Chargaff Purine + Pyrimidine = Perfect Fit from X-ray data

  20. The Race to Discover DNA’s Structure X-Ray diffraction image of DNA taken by Franklin in 1951 Maurice Wilkins Rosalind Franklin

  21. The Race to Discover DNA’s Structure 1953 Compiled data from previous scientists to build a double-helical model of DNA James Watson Francis Crick

  22. Do Now 3.4 • OBJECTIVES: • Describe the process of DNA replication, including the roles and functions of: • Anti-parallel strands • Semi-conservative replication • Key enzymes: Helicase, DNA Polymerase, DNA Ligase • TASK: • Bio 1: Take out flylabs for collection • Bio 3: Flyday VI scheduled for tomorrow… • A molecular biologist is analyzing the DNA of a prokaryote she collected on a research trip. After using enzymes to break the DNA into individual nucleotides, they measure the sample to be 35% guanine. What must the %s of C, T, and A be in the sample?

  23. Notes Begin Where we left off last time…The Race to Discover DNA’s Structure was Over • DNA is made up of: • Four nucleotides: Adenine, Thymine, Guanine and Cytosine • These follow the rules of base-pairing: • Adenine bonds with Thymine • Guanine bonds with Cytosine • A sugar-phosphate backbone • DNA is arranged in a double-helix

  24. DNA Replication • The double helix didn’t quite explain how DNA copies itself • We will study this process, DNA replication, in more detail

  25. How does DNA replicate? Hypotheses: Conservative Semi-Conservative Dispersive

  26. Meselson-Stahl Experiment • Bacteria cultured in medium containing a heavy isotope of Nitrogen (15N)

  27. Meselson-Stahl Experiment • Bacteria transferred to a medium containing elemental Nitrogen (14N)

  28. Meselson-Stahl Experiment • DNA sample centrifuged after First replication

  29. Meselson-Stahl Experiment • DNA sample centrifuged after Second replication

  30. DNA Replication The “parent” molecule has two complementary strands of DNA. Each is base paired by hydrogen bonding with its specific partner: A with T G with C

  31. DNA Replication The first step in replication is the separation of the two strands.

  32. DNA Replication Each parental strand now serves as a template that determines the order of the bases along a new complementary strand.

  33. DNA Replication The nucleotides are connected to form the sugar-phosphate backbones of the new strands. Each “daughter” DNA molecule consists of one parental strand and one new strand.

  34. 3’ (Sugar) DNA has Anti-parallel Strands 5’ (Phos-phate) 5’ (Phos-phate) 3’ (Sugar)

  35. The Process Of Replication • DNA replication involves many enzymes. Several key ones are described on the following slides

  36. Replication Enzymes • Helicase: unwinds DNA

  37. Replication Enzymes • DNA Polymerase: adds nucleotides to the strand at the 3’ end

  38. DNA Polymerase builds new strands in the 5’3’ direction DNA Ligase bonds Okazaki fragments Can you find the replication fork? How about an Okazaki fragment?

  39. The Race to Replicate DNA • Two teams: A and B • Individually, each team member will run to the board to add a nucleotide to the “unzipped” strand of DNA. • The first team to finish base-pairing their DNA correctly will win the game.

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