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DNA STRUCTURE

DNA STRUCTURE. The Chemical Composition of DNA. The Chemical Composition of DNA. 1920s- It was determined that DNA comprises three main components: D eoxyribose sugar P hosphate group Nitrogenous base. Nitrogeneous Bases. Solving the DNA mystery.

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DNA STRUCTURE

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  1. DNA STRUCTURE The Chemical Composition of DNA

  2. The Chemical Composition of DNA • 1920s- It was determined that DNA comprises three main components: • Deoxyribose sugar • Phosphate group • Nitrogenous base

  3. Nitrogeneous Bases

  4. Solving the DNA mystery • 1949- Erwin Chargaff discovered two rules that helped lead to the discovery of the double helix structure of DNA. • This strongly hinted towards the base pair makeup of the DNA, although Chargaff was not able to make this connection himself. G = C A = T Purines = Pyrimidines

  5. Nucleotide Structure in detail

  6. Nucleotides making up DNA

  7. Deoxyribose Sugar • Five-carbon cyclic ring structure • Attached to a phosphate group and nitrogeneous base • The first four of the five carbon atoms, together with an oxygen atom, form a five membered ring • The carbon atoms are numbered clockwise, starting with the carbon atom to the immediate right of the oxygen atom • This first carbon atom is designated as 1' • A deoxyribose sugar has a hydroxyl group (OH) on the 3' carbon, and a hydrogen atom (H) on the 2' carbon

  8. Deoxyribose sugar

  9. Know your bonds:

  10. Building a model for DNA structure • 1953- • California: Linus Pauling • London: Rosalind Franklin & Maurice Wilkins • Cambridge University: James Watson & Francis Crick • Franklin’s X-ray crystallography (X-ray diffraction analysis) results helped Watson and Crick to determine the molecular structure of DNA • X-ray results revealed that DNA has the shape of a helix • DNA has a diameter of 2 nm • A complete helical turn  every 3.4 nm • 1 nm=10-9

  11. Rosalind Franklin James Watson and Francis Crick (1953)

  12. DNA Structure: The Double Helix • DNA consists of two anti-parallel strands of nucleotides • Anti-parallel: parallel running in opposite directions • The bases of one strand are paired with the bases of the other strand • The 5' end of one strand of DNA aligns with the 3' end of the other strand in a double helix.

  13. Complementary Base Pairing • The nitrogeneous base pairs are arranged above each other, perpendicular to the axis of the DNA melecule • A purine is always bonded to a pyrimidine • Adenine with Thymine • Guanine with Cytosine • This type of pairing is termed complementary base pairing

  14. Diameter of DNA is 2 nm If 2 purines are bonded together (A-A or A-G or G-G), the DNA molecule would be wider If 2 pyrimidines are bonded together (T-T or T-C or C-C), the DNA molecule would be less What about Thymine with Guanine? Or Adenine with Cytosine?

  15. DNA • What about Thymine with Guanine? Or Adenine with Cytosine? • Even though, they would have the desired diameter, within the DNA, the molecules would be unstable because of the lack of hydrogen bonding. • Only Adenine can hydrogen bond with Thymine and Guanine can hydrogen bond with Cytosine. • Double helix turns in a clockwise direction • DNA is a right-handed helix making one complete turn every 10 molecules • A full helical twist is 3.4 nm, therefore, the distance between adjacent base pairs is 0.34 nm.

  16. DNA

  17. DNA

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