1 / 43

The History Of DNA

The History Of DNA. Quick Review. Chromosomes are made up of DNA and Proteins . Genes are a segment of the DNA molecule that carries the instructions for producing a specific traits. 1952). DNA or Proteins?.

adelio
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 2006-2007

  2. Honors Biology 2006-2007

  3. Quick Review • Chromosomes are made up of DNA and Proteins. • Genes are a segment of the DNA molecule that carries the instructions for producing a specific traits. Honors Biology 2006-2007

  4. 1952) DNA or Proteins? • Prior to the 1950’s, scientists could not decide whether DNA or protein was the material responsible for heredity. • 3 experiments would lead to the answer: • 1. Frederick Griffith • 2. Avery, McCarty & MacLeod • 3. Hershey & Chase Honors Biology 2006-2007

  5. 1928 Griffith’s Experiment • Frederick Griffith was working to find a cure for Streptococcus pneumonia (bacteria) • Test Subjects: lab mice • He used different strains (types) of bacterium in this experiment. Honors Biology 2006-2007

  6. Strains of Bacteria Used • S Bacteria = Disease Causing (pathogenic) • Have protective outer coat that “hides” the bacteria from the body’s immune defenses. • R Bacteria = Do not cause disease (non-pathogenic) • Lacked the protective coat and thus the immune system can identify and destroy them. Honors Biology 2006-2007

  7. The Experimental Trials mix heat-killed pathogenic & non-pathogenic bacteria live pathogenic strain of bacteria live non-pathogenic strain of bacteria heat-killed pathogenicbacteria A. B. D. C. mice die mice live mice live mice die Transformation? something in heat-killed bacteria could still transmit disease-causing properties Honors Biology 2006-2007

  8. Griffith’s “Transforming Factor” • Why did the mice die that were given a mixture of heat-killed pathogenic bacteria and live non-pathogenic bacteria? • A substance had been passed from the dead bacteria to live bacteria = “Transforming Factor” Honors Biology 2006-2007

  9. Griffith’s Results • After examining blood samples, he found that somehow the uncoated bacteria had TRANSFORMED into bacteria with coats. • Transformation is a change in the genetic makeup caused when cells take up foreign genetic material. BUT, what was it? DNA or Protein?? Honors Biology 2006-2007

  10. What Next? • Whatever the molecule, it had to have several properties in order to fit the bill: • It had to be duplicated whenever a cell divided, so it could be passed on unchanged. • It had to be in the form of an informational code • It had to be (mostly) stable and resistant to change Honors Biology 2006-2007

  11. Avery, McCarty & MacLeod 1944 Oswald Avery Colin MacLeod Maclyn McCarty Honors Biology 2006-2007

  12. DNA causes Transformation • Avery, McCarty & MacLeod • purified both DNA & proteins from Streptococcus pneumonia bacteria • which will transform non-pathogenic bacteria? • Experiment 1: • injected protein into bacteria = no effect • injected DNA into bacteria = transformation! • Experiment 2: • added protein destroying enzymes to bacteria = transformation! • added DNA destroying enzymes to bacteria = no effect Honors Biology 2006-2007

  13. Hershey & Chase Martha Chase Alfred Hershey Honors Biology 2006-2007

  14. 1952 | 1969 Confirmation of DNA • Hershey & Chase • “Blender” experiment using bacteriophages • viruses that infect bacteria • Half of the phages had their proteins tagged with radioactive sulfur (35S) • The other half had their DNA tagged with radioactive phosphorus (32P) • All phage were then allowed to infect bacteria! Honors Biology 2006-2007

  15. Honors Biology 2006-2007

  16. Protein coat labeled with 35S DNA labeled with 32P Hershey & Chase T2 bacteriophages are labeled with radioactive isotopes S vs. P bacteriophages infect bacterial cells bacterial cells are agitated to remove viral protein coats Which radioactive marker is found inside the cell? Which molecule carries viral genetic info? 32P radioactivity foundin the bacterial cells 35S radioactivity found in the liquid Honors Biology 2006-2007

  17. Taaa-Daaa! Blender experiment Results • Radioactive phage & bacteria in blender • 35S phage • radioactive proteins were in liquid • therefore protein did NOT enter bacteria • 32P phage • radioactive DNA was in pellet • therefore DNA did enter bacteria Honors Biology 2006-2007

  18. Hershey & Chase’s Conclusion • Hershey & Chase Confirmed DNA is “transforming factor” • Proved that DNA AND NOT protein is the hereditary material in cells (i.e., genes are made up of DNA) Honors Biology 2006-2007

  19. Wilkin’s and Franklin’s Photographs • In 1952, Maurice Wilkins and Rosalind Franklin, developed high quality X-ray diffraction photographs of strands of DNA. • These photos were key pieces of data used to determine the helical structure of DNA molecules. Honors Biology 2006-2007

  20. 1953 article in Nature Watson and Crick Honors Biology 2006-2007

  21. The Structure of DNA Honors Biology 2006-2007

  22. Deoxyribonucleic Acid • DNA is the molecule of heredity. • DNA (Deoxyribonucleic Acid) is a double-stranded nucleic acid that determines an organism’s traits by controlling the production of proteins. • DNA holds the information for life! • Why do we study DNA?? Honors Biology 2006-2007

  23. DNA’s Size • DNA is an extremely long molecule • DNA from one of your cells would measure 6 feet tall! • All of the DNA in your body could stretch to the sun and back 400 times! The earth is 93 million miles from the sun! • 5 million strands of DNA can fit through the head of one needle! Honors Biology 2006-2007

  24. DNA’s Helical Structure • Watson & Crick discovered DNA is made up of 2 chains of nucleotides joined together by their nitrogen bases. • The 2 strands are twisted together, forming a Double-Helix. • Like a spiral staircase, twisted ladder, or zipper Honors Biology 2006-2007

  25. Subunits of DNA • When we group the deoxyribose sugar, phosphate group and nitrogen base together into a subunit it is called a Nucleotide. • One strand of DNA has many millions of nucleotides. nucleotide Honors Biology 2006-2007

  26. O -P O O O C C Nucleotides Continued • Sugar = Deoxyribose. • The Phosphate Group = Phosphorus atom surrounded by 4 oxygen atoms. • The Nitrogen Bases are carbon ring structures that contain one or more atoms of nitrogen. Nitrogenous base Phosphate O C C C Deoxyribose O Honors Biology 2006-2007

  27. What is DNA made of? phosphate • The backbone of the molecule is alternating phosphate groups and deoxyribose sugars. • The “rungs” of the DNA “ladder” are nitrogenousbases. deoxyribose bases Honors Biology 2006-2007

  28. Four nitrogenous bases • DNA has four different nitrogenous bases: • Adenine (A) • Thymine (T) • Cytosine (C) • Guanine (G) Honors Biology 2006-2007

  29. N N C N C C C N N C Two Classes of DNA Bases • Pyrimidines are single ring bases. • Thymine • Cytosine (Pyrimidins have a “y”) • Purines are double ring bases. • Adenine • Guanine N N C O C C N C Honors Biology 2006-2007

  30. Chargaff’s Rule • The amount of Adenine is always equal to the amount of Thymine. • Adenine and Thymine have a 1:1 ratio • The amount of Guanine is always equal to the amount of Cytosine. • Guanine and Cytosine have a 1:1 ratio Honors Biology 2006-2007

  31. Base pairing in DNA • Pairing • Adenine and Thymine always join together • Two Hydrogen Bonds • Cytosine and Guanine always join together • 3 Hydrogen Bonds • Adenine-Thymine and Guanine-Cytosine are called Complimentary Base Pairs. Honors Biology 2006-2007

  32. hydrogen bonds How do the strands stick? • Hydrogen Bondsform between the nitrogenous bases. • Weak, but there are millions and millions of them in a single molecule of DNA. • Remember hydrogen bonds can form between hydrogen and any electronegative atom! Honors Biology 2006-2007

  33. Nucleotide Sequence • Nucleotide Sequence is extremely important. • Differences in organisms are due to the difference in sequence of the nucleotides along a strand of DNA. • Nucleotide sequence forms the unique genetic information of an organism. Honors Biology 2006-2007

  34. DNA Replication Honors Biology 2006-2007

  35. Copying DNA • Each cell in an organism has an exact copy of the DNA that was in the fertilized egg (Mitosis) • The DNA in the chromosome is copied in a process called DNA Replication. • If DNA wasn’t copied before cell division, new cells would only have half the DNA of their parents. Honors Biology 2006-2007

  36. DNA Replication • Base pairing allows each strand to serve as a pattern (template) for a new strand • Semi-Conservatice Model • 2 molecules are formed. • Each has an original strand and one new strand. Honors Biology 2006-2007

  37. let’s meetthe team… DNA Replication • Large team of enzymes coordinates replication: • DNA Helicase - unwinds the DNA so that it can be copied • DNA Polymerase(s) - Brings in the nucleotide building blocks to make the complimentary strand AND “proofreads” the finished strands. • DNA Ligase - Acts as “glue” cementing new pieces of DNA together to form a continuous strand. Honors Biology 2006-2007

  38. 1st step: Unwinding • Unwind & unzip DNA • helicase enzyme • unwinds DNA helix • stabilized bysingle-stranded binding proteins • The areas where the double helix separate are called replication forks. single-stranded binding proteins Honors Biology 2006-2007

  39. direction of replication Replication fork Honors Biology 2006-2007

  40. Now, that’s a compliment! 2nd step - Adding Bases • DNA Polymerases bring in new nucleotides that match up to template strands Honors Biology 2006-2007

  41. Results of DNA Replication • DNA Replication results in the formation of 2 DNA molecules, each identical to the original DNA molecule. • Each new molecule has one strand from the original DNA molecule and one new strand. • Semi-conservative! Honors Biology 2006-2007

  42. Checking for Errors • Sometimes errors occur when the wrong nucleotide is added to the new strand. • Luckily, DNA Polymerase has a “proofreading function.” • DNA Polymerase can backtrack and remove incorrect nucleotides. Honors Biology 2006-2007

  43. Fast & accurate! • It takes E. coli <1 hour to copy 5 million base pairs in its single chromosome • divide to form 2 identical daughter cells • Human cell copies its 6 billion bases & divide into daughter cells in only few hours • remarkably accurate • only ~1 error per 100 million bases • ~30 errors per cell cycle Honors Biology 2006-2007

More Related