DNA: The Genetic Material - Lesson 1

Module 11, Lesson 1 DNA: The Genetic Material  Focus Question Which experiments led to the discovery of DNA, and which led to the structure of DNA?  Review Vocabulary nucleic acid: complex biomolecule that stores cellular information in the form of a code Discovery of DNA-Scien...

Module 11, Lesson 1 DNA: The Genetic Material  Focus Question Which experiments led to the discovery of DNA, and which led to the structure of DNA?  Review Vocabulary nucleic acid: complex biomolecule that stores cellular information in the form of a code Discovery of DNA-Scientist  Discovery of DNA Frederick Griffith (1928) He carried out experiments that led to the conclusion that a substance can transform bacteria. These experiments set the stage for the search to identify the transforming factor.  Discovery of DNA Griffith’s transformation experiment demonstrated the change of rough bacteria into smooth bacteria.  Discovery of DNA Oswald Avery (1944) He identified the molecule that transformed the R strain of S. pneumoniae into the S strain. Avery concluded that when the S cells were killed, DNA was released. R bacteria incorporated this DNA into their cells and changed into S cells.  Discovery of DNA Alfred Hershey and Martha Chase (1952) They used radioactive labeling to trace bacteriophage DNA and protein. They concluded that the bacteriophage DNA was injected into the cell and provided the genetic information  Discovery of DNA Alfred Hershey and Martha Chase (1952) By radioactively labeling the smooth bacteria DNA before they were killed, one could track the radioactive DNA as it was picked up and incorporated by the rough bacterial cells. He did not use because both proteins and nucleic  Discovery of DNA Summary of Hershey-Chase Results Group 1 Group 2 (Viruses labeled with 32 P) (Viruses labeled with 35 S) Infected Liquid with Infected Liquid with Bacteria Viruses Bacteria Viruses Labeled viral No labeled No labeled Labeled DNA (32P) DNA viral proteins proteins found in the No viral (35S) found bacteria replication Viral No viral Viral replication replication replication occurred occurred New viruses New viruses did not have contained 32P a label  Discovery of DNA Structure  Discovery of DNA Structure Erwin Chargaff He analyzed the amount of A, G, T, and C in the DNA of various species. Chargaff’s rule: C = G and T = A  Discovery of DNA Structure Rosalind Franklin and Maurice Wilkins X-ray diffraction techniques indicated that DNA was a double helix, or twisted ladder shape. The double helix shape was formed by two strands of nucleotides twisted around each other.  Discovery of DNA Structure James Watson and Francis Crick Using Franklin’s and Chargaff’s data, Watson and Crick measured the width of the helix and the spacing of the bases. They built a model that conformed Franklin’s and Chargaff’s data.  Discovery of DNA Structure Important features of the model constructed by Watson and Crick include: Two outside strands consist of alternating deoxyribose and phosphate. Cytosine and guanine bases pair to each other by three hydrogen bonds. Thymine and adenine bases pair to each  Discovery of DNA Structure Nucleotides: are the building blocks of DNA and RNA Nucleotides are the subunits of nucleic acids. They consist of: 5-carbon sugar Phosphate group Nitrogenous base  Discovery of DNA Structure Nucleotides  Discovery of DNA Structure DNA Structure DNA often is compared to a twisted ladder. Rails of the ladder are represented by the alternating deoxyribose and phosphate. The pairs of bases (cytosine-guanine or thymine-adenine) form the steps. Purine base always binds to a pyrimidine base.  Discovery of DNA Structure Orientation DNA molecules have specific orientations of the two strands: The top strand is said to be oriented 5’ to 3’. The bottom strand is oriented 3’ to 5’.  RNA RNA is a nucleic acid similar to DNA, but with only a single, helical strand of bases. It plays a key role in turning DNA instructions into functional proteins  Quiz 1 What are the basic building blocks of DNA. and RNA? A ribose B purines C nucleotidesCORREC T D phosphorus  Quiz 2 If a section of DNA has 27 percent thymine,. how much cytosine will it have? A 23 percent C 46 percent CORREC T B 27 percent D 54 percent  Quiz 3 Which was a conclusion of Griffith’s work. with Streptococcus pneumoniae? A DNA is the genetic C Bacteria exposed material in viruses. to DNA can incorporate the DNA and change CORREC phenotype.T B The structure of D The amount of DNA is a double thymine equals helix. the amount of adenine in DNA.  Quiz 4 Which label. represents the nitrogenous base? A A C C CORREC T B B D D  Quiz 5 What technique did Hershey and Chase. use in their experiment that led to the conclusion that DNA, not protein, was the genetic material in viruses? A transformation C radioactive labelingCORREC T B X-ray diffraction D modeling