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DNA: You study it to discover...

Why is it important? What is its job; its role in life? What is its structure? How was it discovered? What are the chemical “rules” it follows. How does it get created/duplicated? How does it store information? How does the information contained therein get accessed?.

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DNA: You study it to discover...

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  1. Why is it important? • What is its job; its role in life? • What is its structure? • How was it discovered? • What are the chemical “rules” it follows. • How does it get created/duplicated? • How does it store information? • How does the information contained therein get accessed? DNA: You study it to discover...

  2. In the 1800’s, Austrian monk Gregor Mendel outlined the process of how basic 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 contained 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. • It is in these genes where we can find the directions to make us us. • But it took 50 years of research in studies performed by important scientists to figure this out. What Causes Offspring to Look Like Parents?

  3. Today you are going to learn all about the history of discovery and 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

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

  5. Part I: DNA History

  6. So, Mendel knew what happens with basic traits but not how they were stored and transferred. • It has been since discovered this happens through the transmission of DNA from parents to offspring. • DNA is an acronym that a. stands for… DEOXYRIBONUCLEIC ACID • The b. role of DNA is to be the storage molecule for genetic material that contains genes. • Traits we have are “written” into specific areas, called genes, within large, continuous DNA molecules called chromosomes. • A c. gene is the most basic physical unit of heredity containing the instructions to make a trait, …just like a recipe contains the instructions to make a specific food. DNA, the Genetic Material

  7. Searching for the Genetic Material • The concept of genetic material hasn’t been around for very long. As far as the concept goes, DNA is a relatively new discovery. • Three major experiments led to the conclusion that our traits are determined by genetic material and that material is DNA. • These experiments were performed by:

  8. The major question at hand was 1. “What truly determines our traits?” • Griffith was the first researcher credited for helping to answer this. • Griffith discovered that hereditary material responsible for the expression of traits could be transferred between cells and between organisms. • The results of his experimentation led Griffith to discover the process called… • Transformation is a change in genes that is caused when cells take up genetic material from outside sources. Searching for the Genetic Material

  9. 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…

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

  11. Griffith proved hereditary information can be transferred but through what? • 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 to see how the experiment was affected. • Avery’s experiments led to the conclusion that the molecule DNA is responsible for transformation in bacteria. Searching for the Genetic Material

  12. So first hereditary 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?

  13. Hershey and Chase studied bacteriophages. • Bacteriophages are viruses that infects bacteria. Searching for the Genetic Material

  14. By using radioactive isotopes (a chemically-active version of particular elements that emits light when charged with UV radiation) painted in the virus’s DNA and proteins… • Hershey and Chase showed that DNA, not protein (or anything else), is the genetic material being transmitted in viruses... • & all life. Searching for the Genetic Material

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

  16. Discovering DNA’s Structure • The structure of DNA was discovered largely by these three experiments.

  17. The discovery of the structure of DNA was credited to Watson & Crick • but they borrowed information from several other scientists. • Chargaff: • Showed that there was a consistency to the quantity of the bases found in DNA. • 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

  18. 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

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

  20. Discuss with your neighbor one reason why we study scientists for things we already know. • What is the point? • 1 minute, then we’ll discuss. Quick Discussion

  21. Part II: DNA Structure Fill in the handout provided.

  22. The spiral shape of DNA is known as a double helix. • Double = two strands • Helix = spiraled (around itself). The Shape of DNA

  23. DNA looks like one thing, but just like everything else, it’s actually made up of numerous smaller repeating subunits. • The double helix of DNA is made up of chains of individual nucleotides in two separate strands hydrogen bonded to each other down the middle. The Structure of DNA A lot like a zipper

  24. 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

  25. 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

  26. Whereas all subunits of DNA are nucleotides there are 4 different nitrogen bases that give us 4 different nucleotides for DNA. ADENINE GUANINE THYMINE CYTOSINE Nucleotides

  27. P R P R P • The blue ribbon area is known as the BACKBONE • Nucleotides are connected along the BACKBONE. • These are always constructed the same. • PhosphateRibosePhosphateRibosePhosphate… R P R The Shape of DNA

  28. Phosphate Deoxyribose Phosphate DNA Backbone

  29. The two strands are complementary. • This means that the nucleotides on one strand will bond, not to a nucleotide of the same kind, but to a different nucleotide that satisfies the base-paring rules. The Shape of DNA Complements… not mirror images

  30. The Shape of DNA • The two strands are antiparallel. • DNA is made of 2 different strands. • Each backbone are equidistant but going in opposite directions.

  31. The Structure of DNA • The term “anti-parallel” refers to the fact that whereas DNA backbones are equidistant from each other, they are constructed 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. • The hanging phosphate is the 5’ end.

  32. 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 Carbon#1 Ribose C#3 C#2 Anti-Parallel

  33. Label: • The phosphate groups • The sugars • The bases • Draw a line from the name to the appropriate base. • Label the backbone. • Label the 3’ and 5’ ends of both strands. • Label the hydrogen bonds.

  34. DNA uses 4 different bases. • 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, and vice versa. • Specifically, adenine always pairs with thymine, and guanine always pairs with cytosine. Hydrogen Bond Hydrogen Bond Hydrogen Bond More on the Bases

  35. 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 A=T • G triple bonds with CG≡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

  36. Using the information given so far (number of rings & number of bonds) which nucleotide is which? THYMINE 1 Ring 2 Bonds CYTOSINE 1 Ring 3 Bonds ADENINE 2 Rings 2 Bonds GUANINE 2 Rings 3 Bonds Concept Check:

  37. 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

  38. How The Bases Fit Into Larger Molecules

  39. 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. • Phosphate, ribose sugar, nitrogen base. • How the nucleotides are arranged to create strands of DNA. • Complementary & anti-parallel • 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 • CW/HW: Complete the diagram with labels. What to Know at This Point

  40. Label • PHOSPHATES (P) • RIBOSE SUGARS (R) • ADENINE (A) • GUANINE (G) • CYTOSINE (C) • THYMINE (T) • HYRDROGEN BONDS (H-Bond) To solve: Look at the number of rings ( or ) then the number of bonds ( or ) Summary: Complete the Illustration using the rules of complementary bases and h-bonding, determine what each shape is.

  41. Label • PHOSPHATES (P) • RIBOSE SUGARS (R) • ADENINE (A) • GUANINE (G) • CYTOSINE (C) • THYMINE (T) • HYRDROGEN BONDS (H-Bond) To solve: Look at the number of rings ( or ) then the number of bonds ( or ) Summary: Complete the Illustration using the rules of complementary bases and h-bonding, determine what each shape is.

  42. We’re going to stop now. • Get your handout checked for accuracy if you want to. • Otherwise, keep this handout in your notes. You’ll use it again. • Now, reflect on one thing you learned today in your warmups. REFLECT I SAY!

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

  44. 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. • This order of bases is called the “sequence” • Different sequences, called “spellings”, give different genes. • AATGCTAGC could be spelling part of one sequence in one gene • TGCATACCG would be part of another • It’s the same 4 nucleotides, just in a different arrangement. • What we know is that every gene has a particular sequence that is unique for that trait. The Information in DNA

  45. Paired bases on opposite sides of a double helix are said to be complementary because they fit together like puzzle pieces. • 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…. This is the TEMPLATE strand • GACTT This is the COMPLEMENTARY strand • What is the complementary strand for. • CCGTATACCGATTG? • GGCATATGGCTAAC (Template Strand) (Complimentary Strand) The Information in DNA

  46. Pick up an assignment sheet from the back. • This is HOMEWORK and is due by tomorrow. • Scissors and tape are up front. Check in when complete. It’s due tomorrow if not. Homework

  47. 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

  48. Nitrogenous Bases: Categories, pairing

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