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History of DNA

This article provides a brief history of DNA, including its discovery as genetic material and the key scientists involved. It also explains the structure of DNA, including its double helix shape and the composition of nucleotides.

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History of DNA

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  1. History of DNA H Biology Winter 2018

  2. What does DNA stand for? • Deoxyribonucleic acid

  3. What is DNA made of? Which one? • DNA is a macromolecule • Made up of nucleotides • Covalently bonded together • Double stranded • Helix • “Spiral”

  4. What is a nucleotide? • Molecule made of • Deoxyribose sugar • A phosphate group • A nitrogenous base

  5. How was DNA identified as genetic material? • 1928 – Griffith notices that bacteria can transfer some type of material to other types of bacteria • “Transforming principle”

  6. How was DNA identified as genetic material? • 1944 – Oswald Avery discovered that the transforming principle was DNA (genetic material) • 1952 – Hershey and Chase studied a virus that affects bacteria (bacteriophage) and confirmed that DNA was genetic material

  7. How was the structure of DNA discovered? • 1950 – Erwin Chargaff • Noticed that the same 4 bases are found in the DNA of all organisms • Also noticed that: # of Adenine = # of Thymine # of Cytosine = # of Guanine • “Chargaff’s Rule”

  8. How was the structure of DNA discovered? • 1950s – James Watson and Francis Crick • Worked to figure out DNA’s structure • Thought that DNA might be a helix, but had no evidence • Idea that DNA was a helix came from Linus Pauling

  9. How was the structure of DNA discovered? • 1951-1952 – Rosalind Franklin • Used x-ray diffractions to show DNA was truly a double helix • Worked with Maurice Wilkins

  10. How was the structure of DNA discovered? • 1953 – Watson and Crick • Wilkins (a colleague of Franklin) shows Watson and Crick the x-ray pictures • This information gave Watson & Crick the evidence needed to conclude DNA has a helical shape • Made a model of DNA which was made up of two chains of nucleotides

  11. DNA Structure

  12. DNA - Basics • Deoxyribonucleic Acid • Stores and transmits genetic info • Tells the cells which proteins to make and when to make them

  13. DNA - Basics • Made up of nucleotides: • Phosphate group • Sugar • Nitrogen bases (4 total) • Adenine (A) • Thymine (T) • Cytosine (C) • Guanine (G) • Double helix structure (twisted ladder)

  14. All about that base, ‘bout the base…

  15. Nitrogen Bases • 2 groups that bases are put in based on structure • Purines→ 2 carbon rings • Adenine (A) • Guanine (G) • Pyrimidines→ 1 carbon ring • Cytosine (C) • Thymine (T) Pure As Gold Cing Tut lived in a Pyramid

  16. Base Pairing Rules • Adenine (A) always matches w/ Thymine (T) • Cytosine (C) always matches w/ Guanine (G)

  17. Base Pairing Rules • Why these base pairings? • Bases are specific! • Sizes of the bases (rings) • Number of H bonds formed with each other • The sizes of the bases (and how they pair) also determine the structure of the larger DNA molecule

  18. Size of Bases Purine + Purine = Too wide Pyrimidine + Pyrimidine = Too Narrow

  19. NO NO Purine + Pyrimidine = Perfect Fit YES!

  20. What makes up the “backbone” of DNA? • The sides of the ladder are made up of: • 1) Sugar • 2) Phosphate • Alternate along backbone

  21. What Holds Everything Together!? • Weak Hydrogenbonds connect the nitrogenous bases to each other • Covalent bonds connect the sugars and phosphates to each other!

  22. DNA Structure Summary • Double Helix (twisted ladder) • Sides of ladder = sugar/ phosphate backbone • Rungs of the ladder = nitrogen bases

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