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Section 1: The Structure of DNA

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  1. Preview • Bellringer • Key Ideas • DNA: The Genetic Material • Searching for the Genetic Material • The Shape of DNA • The Information in DNA • Discovering DNA’s Structure • Summary Section 1: The Structure of DNA

  2. Read each question, and answer based upon what you learn in the section. 1. With what kinds of bacteria did Griffith inject mice? 2. What was different about the S bacteria and the R bacteria? 3. Why were the heat-killed S bacteria harmless? 4. Why was the mixture of heat-killed S bacteria and R bacteria virulent? 5. What did Griffith discover as a result of his experiments? 6. How did Avery discover that the material responsible for transformation in bacteria was DNA? 7. Viruses that infect bacteria are called [bacteriophages / rough]. 8. A virus is made of DNA and [proteins / cell walls]. 9. Radioactive sulfur was used to label the [DNA / protein] in the viruses. 10. Radioactive phosphorus was used to label the [DNA / protein] in the viruses. 11. Hershey and Chase discovered that after the 32P-labeled phages infected the bacteria, most of the radioactive phosphorus was found in the layer containing [bacteria / phage]. Match the letter of the phrase with the appropriate term _____ 12. double helix _____ 13. nucleotides _____ 14. deoxyribose _____ 15. hydrogen bond _____ 16. nitrogenous bases _____ 17. adenine _____ 18. cytosine _____ 19. Chargaff Explain how the terms in each pair are related to each other. 20. base-pairing rules, complementary 21.Wilkins and Franklin, DNA structure a. a five-carbon sugar b. type of weak bond between base pairs that holds the double helix together c. four kinds and they form specific pairs d. subunits that make up DNA e. one of two pyrimidines used as a nitrogenous base in nucleotides f. one of two purines used as a nitrogenous base in nucleotides g. discovered that the amount of adenine always equaled the amount of cytosine and that guanine always equaled cytosine h. two strands of nucleotides twisted around each other DR 13.1. Section: The Structure of DNA

  3. This is DNA. • What do you know about it? • What is its job & why is it important? • How was it discovered? • What is its structure? • How does it get created? • How does the information contained therein get accessed? DNA

  4. How is the structure of DNA similar to that of a ladder or spiral staircase? How is it different from that of a ladder or spiral staircase? DNA is often compared to a ladder or a spiral staircase. Look at picture to the right and answer the following questions.

  5. What are the 7 properties all living things have on common? • Heredity is one of them. • What is this? • How is the passing of traits from parents to offspring achieved? Properties of Life:Linking to Current Content

  6. In the 1800’s, Austrian monk Gregor Mendel discovered how traits (the physical things you can see on the outside of an organism) are passed on from parent to offspring. • The information Mendel lacked was what these traits were transported in or on. • Physically, how did the trait exist in an organism? • We now know that traits are transferred from parents to offspring through the transfer and sharing of genes contained in DNA. • But it took 50 years of research in studies performed by important scientists. DNA: The Genetic Material

  7. Today you are going to learn all about the basic structure of the molecule that holds our heredity… DNA. • By the end of this lesson you will be able to… • Identify the substance that makes up genetic material. • Name the experiments that identified the role of DNA as the genetic material • Name the studies that led to the discovery of DNA’s structure. • Relate the structure of DNA to the function of DNA as a carrier of information. • Build a model of a DNA molecule. Objectives: DNA Structure

  8. Gene • DNA • Nucleotide • Purine • Pyrimidine Vocabulary

  9. Part I: DNA History

  10. So Mendel knew what happens with traits but not how they were stored and transferred. • Traits are contained in DNA(deoxyribonucleic acid): the primary genetic material that contains genes. • It causes recognizable, inheritable characteristics in related groups of organisms. • Traits are “written” into specific areas, called genes, within the large, continuous DNA molecules called chromosomes. • A gene is the most basic physical unit of heredity • A gene contains the instructions for to make a trait, just like a recipe contains the instructions for a meal. DNA, the Genetic Material

  11. From Cell to Gene

  12. Searching for the Genetic Material • Three major experiments led to the conclusion that DNA is the genetic material in cells. • These experiments were performed by:

  13. Griffith worked with two related strains of bacteria which cause pneumonia in mice. • One strain was deadly… it made the mice sick and killed them. • The other strain did little to nothing to the mice. • Griffith discovered that when harmless live bacteria were mixed with heat-killed disease-causing bacteria and then injected into mice, the mice died. • These results led Griffith to discover transformation. Transformation is a change in genotype that is caused when cells take up foreign genetic material. • Griffith’s experiments led to the conclusion that genetic material could be transferred between cells. Searching for the Genetic Material

  14. Harmless bacteria Deadly bacteria Deadly bacteria that was made harmless because it was boiled to death. Harmless bacteria mixed with killed deadly bacteria… Griffith’s Discovery of Transformation Conclusion… Whatever made the deadly bacteria deadly was being transferred into the harmless bacteria. This process of exchanging information between organisms is called TRANSFORMATION…

  15. So first, genetic material is known to exist and it can be transferred in a process called transformation.

  16. Griffith proved hereditary information can be transferred but what was it? • Avery wanted to determine whether the transforming agent in Griffith’s experiments was protein, RNA, or DNA. • Avery used enzymes to destroy each of these molecules in heat-killed bacteria. • Avery’s experiments led to the conclusion that DNA is responsible for transformation in bacteria. Searching for the Genetic Material

  17. So first genetic material is known to exist and it can be transferred in a process called transformation. • Then we knew that DNA was the genetic material being passed on…but was it the only genetic material?

  18. Hershey and Chase studied bacteriophages. • Bacteriophages are viruses that infects bacteria. • By using radioactive isotopes (chemical that emit light when charged with UV radiation) painted in the virus’s DNA and proteins, Hershey and Chase showed that DNA, not protein, is the genetic material in viruses. Searching for the Genetic Material

  19. So first genetic material was known to exist and it can be transferred. – Griffith • Then we knew that DNA was the genetic material being passed on…but was it the only genetic material? – Avery • Next a discovery lead to the realization that DNA, not anything else, was responsible for containing the genetic information that is passed between organisms. – Hershey & Chase • The next question…What is the structure?...

  20. Discovering DNA’s Structure • The search for DNA’s structure was headed by several scientists that each contributed a little at a time:

  21. The discovery of the structure of DNA was credited to Watson & Crickbut they borrowed information from several other scientists. • Chargaff: • Showed that the amount of adenine always equaled the amount of thymine • & the amount of guanine always equaled the amount of cytosine. • Franklin and Wilkins: • Developed X-ray diffraction images of strands of DNA that suggested the DNA molecule resembled a tightly coiled helix. Discovering DNA’s Structure

  22. Watson and Crick used both Chargaff’s data and the X-ray diffraction studies to create a complete three-dimensional model of DNA. • Their model showed a “spiral staircase” in which two strands of nucleotides twisted around a central axis. • These pictures are looking straight down the staircase. Discovering DNA’s Structure, continued

  23. What were the three experiments that lead to the discovering what the genetic material in humans was? • What is the name of the molecule that contains genetic information? • Who is credited for discovering the structure of DNA? • Name two other contributing scientists and what they discovered. Concept Check:

  24. Part II: DNA Structure

  25. The spiral shape of DNA is known as a double helix. The Shape of DNA

  26. DNA is made up of individual nucleotides bonded to each other. The Shape of DNA

  27. A nucleotide is a DNA subunit made up of three parts: a phosphate group, a 5-carbon sugar group, and a nitrogen-containing base. • The five-carbon sugar in DNA is called deoxyribose, from which DNA gets its full name, deoxyribonucleic acid. • “de” means removed = it lacks one hydroxide group present in RNA The Structure of DNA

  28. The two strands are antiparallel. • The backbones are equidistant but going in opposite directions. The Shape of DNA

  29. The Structure of DNA • The term “anti-parallel” refers to the fact that whereas DNA backbones are equidistant from each other, they go in opposite directions. • One strand goes in the 3’5’ direction • The other goes in the 5”  3’ direction • The 3’ or 5’ refers the carbons in the ribose sugar.

  30. Ribose is a 5-carbon sugar. • 5’ refers to the end of the nucleotide closest to the #5 carbon. • 3’ refers to the end of the nucleotide closest to the #3 carbon. C#5 C#4 C#1 Ribose C#3 C#2 Anti-Parallel

  31. The two strands are complimentary. • One strand contains bases that are complimentary to the other strand’s bases. The Shape of DNA Compliments… not mirror images

  32. The blue ribbon area is known as the BACKBONE • These are always the same. • PhosphateRibosePhosphateRibosePhosphate… The Shape of DNA

  33. Phosphate Deoxyribose Phosphate DNA Backbone

  34. DNA is held together by hydrogen bonds. • They are represented by dashed lines. • Notice the # of H-bonds. They change depending on the bases involved. Hydrogen Bonds Hydrogen Bonds Hydrogen Bonds Hydrogen Bonds DNA: Hydrogen Bonding

  35. Visual Concept: DNA Overview

  36. The four kinds of bases are adenine (A), guanine (G), thymine (T), and cytosine (C). • Bases A and G have a double-ring structure and are classified as purines. • Bases T and C have a single-ring structure and are classified as pyrimidines. • A purine on one strand of a DNA molecule is always paired with a pyrimidine on the other strand. • Specifically, adenine always pairs with thymine, and guanine always pairs with cytosine. Hydrogen Bond Hydrogen Bond Hydrogen Bond The Bases Hydrogen Bond Hydrogen Bond

  37. Base-pairing rules (as given to us by Chargaff) are dictated by the chemical structure of the bases. • It has to do with the category (purine/pyrimidine) as well as their hydrogen bonding characteristics. • A double bonds with T • G triple bonds with C • The bonds are HYDROGEN BONDS • Whereas hydrogen bonds are weak individually, the billions of bonds between bases keep the two long strands of DNA together. Base-Pairing

  38. The “puzzle piece” refers to the hydrogen bonding between the paired bases. Guanine and cytosine have 3 hydrogen bonds whereas thymine and adenine have 2 hydrogen bonds. Complimentary Bases

  39. How The Bases Fit Into Larger Molecules

  40. Visual Concept: Complementary Base Pairing

  41. The three experiments that lead to the discovery of DNA as the genetic material. • Who contributed to the discovery of the structure of DNA? • The structure of DNA • What a nucleotide is composed of. • How the nucleotides are arranged to create strands of DNA. • What holds the bases together…Hydrogen Bonds (H-bonds) • The base-paring rules • A – T, C – G, pyrimidine, purine. • How many hydrogen bonds between the bases • HW: Complete the half-sheet. Fill in all shapes with abbreviations for the part that goes there. Label the hydrogen bonds too. What to Know at This Point

  42. Summary: Complete the Illustration in your notes.Using the rules of complementary bases and h-bonding, determine what each shape is. To solve: Look at the number of rings then the number of bonds…

  43. Ribose Nitrogenous base Tyrosine Phosphate Phosphate Nitrogenous base Adenine Ribose Ribose Nitrogenous base Guanine Phosphate Phosphate Nitrogenous base Cytosine Ribose

  44. Take out your homework • The half sheet you had from yesterday. • We’ll discuss in 5 minutes. • Make sure you check with neighbors and get clarification on anything you couldn’t get. Day 2

  45. The information in DNA is contained in the order of the bases. • The order of how the bases are arranged determines the trait that will result. • Different arrangements, called “spellings”, give different genes. • AATGCTAGC would be part of one gene • TGCATACCG would be part of another • It’s the same stuff, just a different arrangement • & The strict base-pairing structure allows the information to be stored and copied. The Information in DNA

  46. Paired bases are said to be complementary because they fit together like puzzle pieces. • Think about Dr. Watson explaining the bonds in the video. • Because of base-pairing rules, if the sequence (the order) of bases is known for one strand of DNA, then the sequence of bases for the complementary strand (the other) can be quickly identified or predicted. • Ex. CTGAA BONDS WITH…. • GACTT this is the complimentary strand • What is the complimentary strand for. • CCGTATACCGATTG? • GGCATATGGCTAAC The Information in DNA, continued

  47. Pick up an assignment sheet from the back. • This is HOMEWORK and is due by tomorrow. • Scissors and tape are up front. Homework

  48. DNA is the primary material that causes inheritable characteristics in related groups of organisms. • Three major experiments led to the conclusion that DNA is the genetic material in cells. These experiments were performed by Griffith, Avery, and Hershey and Chase. • A DNA molecule is shaped like a spiral staircase and is composed of two parallel strands of linked subunits. • The information in DNA is contained in the order of the bases, while the base-pairing structure allows the information to be copied. • Watson and Crick used information from experiments by Chargaff, Wilkins, and Franklin to determine the three-dimensional structure of DNA. Summary

  49. Nitrogenous Bases: Categories, pairing