1 / 22

The History of DNA

The History of DNA. Honors Biology Chapter 12 Section 1. Griffith. 1928 Fredrick Griffith studying how bacteria made people sick and how different types of bacteria caused pneumonia

solana
Download Presentation

The History of DNA

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The History of DNA Honors Biology Chapter 12 Section 1

  2. Griffith • 1928 Fredrick Griffith studying how bacteria made people sick and how different types of bacteria caused pneumonia • Isolates 2 strains (types) of bacteria from mice. Disease causing (grows in smooth colonies) and non-disease causing (grows in rough colonies) • Injects mice with disease causing: mice get pneumonia and die • Injects mice with non-disease causing: mice survive

  3. Griffith • Griffith wonders if disease causing bacteria produce a toxic poison??? • Griffith takes disease causing bacteria and heats it to kill the bacteria. Injects the heat killed bacteria into mice: mice survive • Griffith mixes heat killed bacteria with the non-disease causing bacteria injects into mice: mice get pneumonia and die

  4. Griffith • Somehow the heat killed bacteria had passed their disease causing ability to the harmless strain • Griffith called this process transformation because the non-disease causing bacteria had been changed to disease causing • Griffith hypothesized that when the 2 strains were mixed, one factor was transferred from one strain of bacteria to the other. That factor had the ability to be passed from 1 generation to the next, transforming factor might be a gene

  5. Video of Griffith Experiment

  6. Griffith

  7. Avery • 1944 Scientists wanted to know which molecule of the heat killed bacteria was required for the transformation • Took an extract from the heat killed bacteria and added enzymes that destroyed proteins, transformation still occurred • Repeated procedures for lipids, carbs and RNA, transformation still occurred • Repeated procedures for DNA, transformation did not occur

  8. Avery • CONCLUSION: DNA was the transmitting factor • Concluded that the nucleic acid DNA stores and transmits the genetic information from 1 generation to the next

  9. Hershey and Chase • 1952 Studied viruses, non-living particles that infect living organisms. Studied bacteriophage which means “bacteria eater”. Consists of a DNA or RNA core and a protein coat. • When bacteriophage infects a bacterium, the virus attaches, injects it’s genetic info. The viral genes produce many bacteriophages until they destroy the bacterium. The cell splits open and 100’s of bacteriophages burst out

  10. Bacteriophage

  11. Hershey and Chase • Reasoned that if they could determine which part of the virus (protein coat or genetic info) infected the cell, they could determine whether genes were made from DNA or protein • Used isotopes of phosphorus 32 and sulfur 35 protein does not contain phosphorus DNA and RNA does not contain sulfur • Radioactive isotopes used as markers

  12. Hershey and Chase • DNA and RNA marked with phosphorus • Protein marked with sulfur • Mixed viruses with the bacteria for radioactivity • All of the radioactivity in the bacteria was from phosphorus 32 the marker found in DNA • Conclusion: the genetic material of the bacteriophage was DNA and not the protein coat

  13. Hershey and Chase

  14. Components and Structure of DNA • DNA is a long molecule made of units called nucleotides • Each nucleotide made of a 5 carbon sugar called deoxyribose, a phosphate group and a nitrogen base. Hence DNA stands for Deoxyribonucleic acid • There are 4 nitrogen bases: adenine, guanine, thymine and cytosine • Adenine and guanine belong to a group called the purines whose structure contains 2 rings • Cytosine and thymine belong to a group called the pyrimidines whose structure contains 1 ring

  15. Components and Structure of DNA • The backbone of a DNA chain is made of the deoxyribose sugars and phosphate groups of each nucleotide • The nucleotides may be joined in any sequence • Although there is only 4, many combinations are possible (alphabet analogy)

  16. DNA Nucleotides

  17. Chargaff’s Rules • Discovered the following, known as chargaff’s rule amount of cytosine (c) = amount of guanine (g) amount of adenine (a) = amount of thymine (t)

  18. Rosalind Franklin • 1952 used an xray beam to help determine structure of DNA. The xrays diffracted on film providing specific patterns for the shape of DNA • The x shaped pattern • Suggested DNA was a double helix, double stranded and nitrogen bases were at center of molecule • Died at age 37 from cancer

  19. Watson and Crick • 1953 James Watson and Francis Crick developed a 3D model of DNA from cardboard and wire • Watson shown a pic of Franklin’s x-ray “my mouth fell open and my pulse began to race” • Model was a double helix – 2 strands wound around each other • Later discovered that the forces that held the nitrogen bases together were hydrogen bonds • Hydrogen bonds can only form between certain base pairs, A and T & C and G • Came up with the idea of base pairing which explained chargaff’s rule: A bonds with T and C bonds with G

  20. Watson and Crick

  21. DNA Structure

  22. Assignment • Create a time line of the scientific findings that led us to the discovery of the structure and function of DNA BE CREATIVE!!!!!!! • Due tomorrow

More Related