3Deoxyribonucleic acid What is DNA?Deoxyribonucleic acidDNA is the molecule of genes.It is found in the chromosomes.It holds the instructions to making all the proteins in an organism.
4Proteins make up the structures of cells. Proteins, in the form of enzymes, also control all cell processes.
5DNA carries the instructions from mother to daughter cells, from parents to children. Therefore it is the molecule of heredity.mitosis sexual reproduction
6Who discovered DNA?Deoxyribonucleic acid (DNA) was first isolated in 1869 by the Swiss scientist Friedrich Miescher. He called the white, slightly acidic chemical that he found in cells "nuclein." He identified DNA as part of a chromosome in 1871.
7Did DNA or Protein makeup a molecule of heredity? By the 1920s it was thought that genes were made of protein, the other main ingredient of the chromosome. Many scientists at the time thought DNA was too simple to carry genetic information. ---They were wrong! thought that proteins were molecules of heredity.
8How did scientists discover that DNA was the hereditary molecule? Scientists such as the Griffith’s bacteria experiment in 1928, and Avery’s bacteria experiment in 1944, pointed toward DNA.The famous Hershey-Chase experiment finally ended the debate.Oswald Avery
9Hershey-Chase: The “Waring Blender” experiment – 1952. Alfred Hershey and Martha Chase
10They experimented with bacteriophages, viruses that infect bacterial cells. These viruses are basically composed of protein surrounding DNA.
11Bacteriophage viruses force bacteria cells to make new virus particles. The experiment would see if the virus’ proteins or the virus’ DNA caused the bacteria to produce the new virus particles.
12Hershey and Chase grew the viruses in a mixture of radioactive isotopes of elements found mainly in either the DNA (phosphorus-32) or in the Protein (sulfur-35).The viruses were mixed with bacteria. After a few minutes, the viruses were separated from the bacteria.They used a blender to do this which is why it is sometimes referred to as the “Waring Blender Experiment.”
13The bacteria were then tested for phosphorus-32 (32P) and sulfur-35 (35S). Nearly all the radioactivity in the bacteria was phosphorus-32 (32P), the isotope that marked the DNA!
14Conclusion: The genetic material of the bacterophage viruses was not the protein but DNA. DNA is the molecule of heredity!
15Rosalind Franklin and Maurice Wilkins examined DNA in the laboratory to determine its structure.
16X-Ray Diffraction (X-Ray Crystallography) photograph of DNA, taken by Rosalind Franklin was very important to the scientists who eventually discovered the structure of DNA.“photo 51”
20Watson & Crick in their Cambridge office c. early1950s
21Watson, Crick and Wilkins shared the Nobel Prize in Physiology or Medicine in1962. Unfortunately, Franklin had died of breast cancer prior to the award.Rosalind Franklin, seen here serving coffee in evaporating dishes at her Parisian laboratory in the late 1940s, went on to publish an impressive array of scientific papers in the decade she had remaining to her.MMMMM!Evaporating Dish Coffee!
22What is DNA’s Structure? DNA is a biological polymer made up of subunits called nucleotides.DNA Nucleotides are made up of:a) 5-carbon deoxyribose sugarb) phosphate groupc) nitrogen-containing baseBy the way ---the sugar and base alone make up a nucleoside
23There are two classes of nitrogen bases: Purines (double ring structure)adenine (A) guanine (G)Pyrimidines (single ring structure) cytosine (C) thymine (T)
24Mnemonic Device All that is Good is Pure. C (see) The pyramids. Adenine Guanine purinesCytosine Thymine pyrimidines
25Another discovery that helped Watson & Crick Erwin Chargaff - demonstrated that guanine and cytosine are always in equal amounts (as well as thymine & adenine)
26Rosalind Franklin’s X-Ray evidence showed, among many other things, that DNA has the shape of a double helix or “twisted ladder.”
27Summary of DNA’s Structure: Note: A & T are not labeledcorrectly in the animationSummary of DNA’s Structure:Alternating sugars & phosphates on the sides of the ladder. (Covalently-bonded)2) Nitrogen bases in the rungsA-T , G-C (base-paring)Note: A & T are not labeledcorrectly in the animation