Más contenido relacionado


DNA double helix

  1. Double Helical structure of DNA By A Rehman B Tech. Food Technology 1
  2. Learning objectives: • To get familiar with the term DNA • Discovery of DNA • Contribution of major scientists in the field of Nucleic acid • Primary, Secondary and Tertiary structures of DNA • Applications and functions of DNA 2
  3. DNA • DNA - a polymer of deoxyribo nucleotides • found in chromosomes, mitochondria and chloroplasts • carries the genetic information 3
  4. 4
  5. DNA (Deoxyribo Nucleic Acid): By Structure DNA is a double stranded molecule that is twisted into a Helix (Spiraling staircase) (Spiraling Staircase) DNA Double Helix 5
  6. DNA: Major Contributions 6
  7. Rosalind Franklin James Watson Francis Crick Maurice Wilkins 7
  8. Franklin’s Work 8
  9. In 1951 Rosalind Franklin discovers the Two Forms of DNA through her X-ray diffraction images. A – Dry Form B – Wet Form Two forms of DNA 9
  10. Watson and Crick’s Work 10
  11. • 1951 James Watson traveled from the United States to work with Francis Crick at Cambridge University • Watson and Crick used the “Model Building” approach • They physically built models out of wire, sheet metal, nuts and bolts to come up with the structure of DNA Watson and Crick’s Work 11
  12. How Watson and Crick Solved the DNA Structure • They already knew from Franklin and Wilkins’ work that DNA was in the form of a Double Helix • They used Chargaff’s Rule to figure out how the 4 Bases match up in pairs Diagram representing X-ray diffraction images 12
  13. How Watson and Crick Solved the DNA Structure They discovered that: • The Phosphate Backbone was on the outside • Which protected the Bases on the inside • DNA acts as a Template or a Copying Mechanism for reproduction 13
  14. DNA Structure: Achievements Watson and Crick alongwith Wilkins won the Nobel Prize in Physiology/ Medicine (1962) for their discovery of the DNA double helix Structure. 14
  15. DNA Structure •Primary •Secondary •Tertiary 15
  16. DNA Structure : Primary Structure • Consists of a linear sequences of nucleotides. linked together by phosphodiester bonds. • Nucleotides consists of three components: 1. Nitrogenous base Adenine Guanine Cytosine Thymine (present in DNA only) Uracil (present in RNA only) 2. 5-carbon sugar which is called deoxyribose (found in DNA) and ribose (found in RNA). 3. One or more phosphate groups. 16
  17. Each strand consists of 1.Nitrogenous base •Adenine ●Cytosine •Guanine ●Thymine 17
  18. Each strand consists of: 2) A Sugar Phosphate backbone 18
  19. Each strand consists of: 1) Nitrogenous base 2. Sugar Phosphate Backbone 19
  20. DNA structure • made up of molecules called nucleotides 20
  21. Components of a nucleotide Base Sugar Phosphate 21
  22. 22
  23. The secondary structure of DNA Two anti-parallel polynucleotide chains wound around the same axis. Sugar-phosphate chains wrap around the periphery. Bases (A, T, C and G) occupy the core, forming complementary A · T and G · C Watson-Crick base pairs. 23
  24.  hydrogen bonding;  base stacking The DNA double helix is held together mainly by- Hydrogen bonds 24
  25. HYDROGEN BOND • a chemical bond in which a hydrogen atom of one molecule is attracted to an electronegative atom, especially a nitrogen, oxygen, or fluorine atom, usually of another molecule. 25
  26. Helical sense: right handed Base pairs: almost perpendicular to the helix axis; 3.4 Å apart One turn of the helix: 36 Å; ~10.4 base pairs Minor groove: 12 Å across Major groove: 22 Å across Normally hydrated DNA: B-form DNA 26
  27. DNA Tertiary Structure •DNA double helical structure coils round histones. •Nucleosomes (10nm fibres) •Nucleosomes contain 146 nucleotides 27
  28. Applications of DNA • Science and technology have advanced since the discovery in year 1953. • Some achievements that potentially became successful due to its invention. Cloning Genetically Modified Foods (GMFs) Genetic Engineering DNA Fingerprinting/ Analysis 28
  29. Functions of DNA and summary of structure • DNA consists of four bases—A, G, C, and T—that are held in linear array by phosphodiester bonds through the 3' and 5' positions of adjacent deoxyribose moieties. • DNA is organized into two strands by the pairing of bases A to T and G to C on complementary strands. These strands form a double helix around a central axis. • The 3 x 109 base pairs of DNA in humans are organized into the haploid complement of 23 chromosomes. • DNA provides a template for its own replication and thus maintenance of the genotype and for the transcription of the roughly 30,000 human genes into a variety of RNA molecules. 29
  30. Thank You 30

Notas del editor

  1. pat
  2. pat
  3. matt
  4. Mat
  5. sanaz
  6. pat
  7. pat