1 / 18

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.

dyan
Télécharger la présentation

DNA STRUCTURE

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related