DNA Discovery and Structure Interest Grabber Order! Genes are made of DNA, a large, complex molecule. DNA is composed of individual units called nucleotides. Three of these units form a code. The order, or sequence, of a code and the type of code determine the meaning of the message. 1. On a sheet of paper, write the word cats. List the letters or units that make up the word cats. 2. Try rearranging the units to form other words. Remember that each new word can have only three units. Write each word on your paper, and then add a definition for each word. 3. Did any of the codes you formed have the same meaning? 4. How do you think changing the order of the nucleotides in the DNA codon changes the codon’s message? Go to Section:

DNA Discovery and Structure Section Outline 12–1DNA A.Griffith and Transformation 1.Griffith’s Experiments 2.Transformation B.Avery and DNA C.The Hershey-Chase Experiment 1.Bacteriophages 2.Radioactive Markers D.The Structure of DNA 1.Chargaff’s Rules 2.X-Ray Evidence 3.The Double Helix Section 12-1 Go to Section:

DNA Discovery and Structure Discovery of Genetic Material Mendel’s work actually created more questions in the minds of scientists. What are genes made of? Chromosomes consist of two materials DNA wrapped around a protein. Which of the two materials carried the genetic code? Transformation A process where one strain of bacteria is changed to another

DNA Discovery and Structure KEY CONCEPT DNA was identified as the genetic material through a series of experiments.

DNA Discovery and Structure

DNA I.Deoxyribonucleic Acid A.Chromatin/chromosomes B.In nucleus C.Functions: i.Stores, copies & transmits genetic information (genes); genes code for proteins determining cell functions & traits

13.1 Ecologists Study Relationships Is DNA the genetic material? 3 experiments = evidence Frederick Griffith – discovers that a heritable factor in bacteria can transform harmless bacteria into deadly bacteria in mice II. A Genetic Mystery

DNA Discovery and Structure 1. Griffith’s Transformation An army medical officer attempting to develop a vaccine against pneumonia, but unexpectedly advances molecular biology instead isolated and cultured two different strains of the pneumonia bacteria R = rough surface, not deadly S = smooth surface (protein coat), deadly Turn to p 339 in your book.

DNA Discovery and Structure TWO types of Streptococcus pneumonia a. Smooth edged colony (S type) - have a polysaccharide (sugar) capsule around the bacteria's cell membrane:capsule which protects the bacteria from the cell's defenses and causes PNEUMONIA b. Rough edged colony (R type) - lack the sugar capsule and does not cause pneumonia

DNA Discovery and Structure Griffith’s Transformation CLUE: Live S cells found in mouse body injected with heat-killed S cells!!!!

DNA Discovery and Structure What Happened? Maybe the heat-killed “S” cells in the mixture weren’t really killed. If this was true, what would have happened to the mice in Experiment 3? Maybe the harmless “R” cells in the mixture can mutate into a killer form. If this was true, what would have happened to the mice in Experiment #1?

DNA Discovery and Structure DISCOVERY: 1) The heat killed = harmless R bacteria was changed (transformed) into the deadly S form of bacteria 2) Genetic material transferred between dead bacteria and living bacteria. WHY did transformation take place? What was transferred to the R bacteria? We know now that some bacteria can take up DNA released from other cells and use it.

DNA Discovery and Structure The Importance of Griffith’s Work Griffith called this “transformation.” He had shown that something had been transferred from the heat-killed disease-causing bacteria to the live harmless bacteria that could be inherited.. Investigators began searching for this unknown material.

13.1 Ecologists Study Relationships Oswald Avery – shows that DNA is the factor in Griffith’s experiment by selectively destroying different types molecules & checking whether transformation still occurred II. A Genetic Mystery

DNA Discovery and Structure Oswald Avery's Experiment (1944) Project: Repeat Griffith's experiment with a TWIST R bacteria + "Heat killed" S bacteria mixture: Used an ENZYME that destroyed RNA and sugars (polysaccharides) RESULT: Transformation still took place and the mice died. R bacteria + "Heat killed" S bacteria mixture: Used an ENZYME that destroyed DNA. RESULT: Transformation did not take place, and mice lived!!!

DNA Discovery and Structure Avery’s Experiments CLUE: Only culture not transformed is treated with DNAse (enzyme cuts up DNA).

DNA Discovery and Structure DISCOVERY: 1) DNA-destroying enzymes prevented harmless bacteria from transforming into deadly bacteria 2) DNA was the genetic material NOT protein.

13.1 Ecologists Study Relationships Alfred Hershey & Martha Chase - use radioactive markers to trace where DNA and proteins are located during a bacteriophage infection; supports Avery. DNA is the genetic material! II. A Genetic Mystery

DNA Discovery and Structure Alfred Hershey and Martha Chase Experiment (1952) Background of Experiment: Studied the effect of a bacteriophage on bacteria BACTERIOPHAGE = a virus that infects bacteria only Bacteriophage attaches to bacteria and injects its DNA into the bacteria - protein capsule remains outside the Bacteria. DNA becomes part of the bacteria's DNA - instructs the bacteria to make hundreds of new phages. Bacteria becomes full of new virus and finally bursts - releasing new bacteriophages

DNA Discovery and Structure Hershey and Chase confirm that DNA is the genetic material. Hershey and Chase studied viruses that infect bacteria, or bacteriophages. Tagged DNA was found inside the bacteria; tagged proteins were not. – They tagged viral DNA with radioactive phosphorus. – They tagged viral proteins with radioactive sulfur.

DNA Discovery and Structure Hershey & Chase

DNA Discovery and Structure Hershey & Chase Clue: Radioactivity inside cell only when attached to DNA

DNA Discovery and Structure Mystery Solved: All evidence points to DNA as the genetic material. No evidence points to protein. II. A Genetic Mystery

DNA Discovery and Structure Checkpoint 1.What is the function of DNA? 2.What is the molecular function of genes? 3.Describe the three experiments that demonstrated that DNA must be the genetic material? 24 ANY QUESTIONS?

DNA Discovery and Structure III. A Race to DNA Structure Once known that DNA is the molecule of heredity – new question: HOW DOES IT WORK? Like all biological molecules and their chemistry, the key to function lies in their structure! Probably the most important biological discovery of the 20 th century.

DNA Discovery and Structure Competition, personality clashes and secret collaborations describe the race to be the first to find the actual molecular structure of DNA. What did we know in 1920? – DNA is a nucleic acid. III. A Race to DNA Structure

DNA Discovery and Structure KEY CONCEPT DNA structure is the same in all organisms.

DNA Discovery and Structure A. DNA is a Nucleic Acid 1.nucleic acid - chains of nucleotides linked by covalent bonds. 2.DNA Nucleotide a)phosphate, b)deoxyribose (sugar) c) Nitrogen base

DNA Discovery and Structure 2. DNA Nucleotide O O=P-O O Phosphate Group N Nitrogenous base (A, G, C, or T) CH2 O C1C1 C4C4 C3C3 C2C2 5 Deoxyribose (sugar) Draw & label in your notes

DNA Discovery and Structure The nitrogen containing bases are the only difference in the four nucleotides.

DNA Discovery and Structure PurinesPyrimidines AdenineGuanine CytosineThymine Phosphate group Deoxyribose Figure 12–5 DNA Nucleotides Section 12-1 Go to Section:

DNA Discovery and Structure T A C G Nucleotides always pair in the same way. The base-pairing rules show how nucleotides always pair up in DNA. Because a pyrimidine (single ring) pairs with a purine (double ring), the helix has a uniform width. – A pairs with T – C pairs with G

DNA Discovery and Structure Percentage of Bases in Four Organisms Section 12-1 Source of DNAATGC Streptococcus Yeast Herring Human Streptococcus Yeast Herring Human Go to Section:

DNA Discovery and Structure Purines = pyrimidines in a DNA sample B. Chargaff’s Rules – 1949 Erwin Chargaff - amount of Adenine always equal to amount of Thymine, Cytosine always equal to Guanine and amount of Purines = pyrimidines in a DNA sample III. A Race to DNA Structure Due to Base Pair Rules: A bonds with T & G bonds with C

DNA Discovery and Structure Checkpoint Quiz 1.What kind of macromolecule is DNA? 2.What are the three parts of a nucleotide? 3.How do you tell purines and pyrimidines apart? 4.Which bases are paired together? 5.According to Chargaff’s rules, if 30% of DNA sample is Adenine, how much is Thymine? 6.How much is Cytosine? 3535 ANY QUESTIONS?

DNA Discovery and Structure How do these 4 building blocks fit together to form the molecule responsible for all of the similarity and diversity of LIFE?? C Linus Pauling – Nobel American chemist uses modeling (toys!) to propose first structure. – he suggests a triple helix DNA III. A Race to DNA Structure

DNA Discovery and Structure D Rosalind Franklin & Maurice Wilkins capture X-ray pattern of DNA – key clue to structure; not a triple helix Hated each other but worked in same lab III. A Race to DNA Structure

DNA Discovery and Structure

Watson and Crick’s discovery built on the work of Rosalind Franklin and Erwin Chargaff. –Franklin’s x-ray images suggested that DNA was a double helix of even width. –Chargaff’s rules stated that A=T and C=G.

DNA Discovery and Structure At the college down the road, two students, using Pauling’s models, see Franklin’s photo from Wilkins and publish their own idea – WITHOUT crediting Franklin! III. A Race to DNA Structure

DNA Discovery and Structure E Watson & Crick reveal 3-D model of DNA molecule: DOUBLE HELIX with 2 complementary antiparallel strands joined by hydrogen bonds between base pairs III. A Race to DNA Structure - used the information from the above scientists and established the structure of DNA (with the unknowing help of Rosalind Franklin)

DNA Discovery and Structure Watson and Crick determined the three-dimensional structure of DNA by building models. They realized that DNA is a double helix that is made up of a sugar- phosphate backbone on the outside with bases on the inside.

DNA Discovery and Structure Hydrogen bonds Nucleotide Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Figure 12–7 Structure of DNA Section 12-1 Go to Section:

DNA Discovery and Structure III. A Race to DNA Structure 1.Double Helix – 2 strands in a twisted ladder with covalent bonded sugar-phosphate rails and H-bonded base pair rungs 2.Complementary – strands match according to base pairing rules (A-T, C-G) If know one strand, then can code for the other. If know one strand, then can code for the other. Important for copying! Important for copying!

DNA Discovery and Structure DNA Model 3.Antiparallel = 2 strands of DNA run in opposite directions (5’ carbon v 3 ’ carbon at end) Draw & label in your notes Sugar- phosphate rail 3’ 5’

DNA Discovery and Structure E Franklin dies of cancer at 37. F Watson & Crick (& Wilkins) Win Nobel Prize for double helix DNA III. A Race to DNA Structure

DNA Discovery and Structure Checkpoint 1.Who is credited with the double helix model? 2.What is a double helix? 3.Which nucleotide parts make up the rails of a DNA molecule? 4.Which nucleotide parts make up the rungs? 5.If a DNA strand reads ATCGTAG, what does the complementary strand read? 47 ANY QUESTIONS?