Se ha denunciado esta presentación.
Se está descargando tu SlideShare. ×

Structure of DNA for medical school

Cargando en…3

Eche un vistazo a continuación

1 de 55 Anuncio

Más Contenido Relacionado

Presentaciones para usted (20)

A los espectadores también les gustó (20)


Similares a Structure of DNA for medical school (20)

Más de Ravi Kiran (20)


Más reciente (20)

Structure of DNA for medical school

  2. 2. V.S.RAVIKIRAN, MSc., Department of Biochemistry, ASRAM Medical college, Eluru-534005.AP, India.
  4. 4. The “central dogma” of Molecular Biology
  5. 5. 12
  6. 6. NUCLEIC ACIDS: INFORMATIONAL POLYMER • Nucleic acids are polymers of monomer units called nucleotides • Nucleic acids store and transmit hereditary information: gene • Two major forms of nucleic acid polymers: DNA and RNA
  7. 7. DNA (Deoxyribonucleic Acid)
  8. 8. DNA Structure DNA is a nucleic acid. The building blocks of DNA are nucleotides, each composed of: – a 5-carbon sugar called deoxyribose – a phosphate group (PO4) – a nitrogenous base • adenine, thymine, cytosine, guanine
  9. 9. 17 DNA Structure The nucleotide structure consists of – the nitrogenous base attached to the 1’ carbon of deoxyribose – the phosphate group attached to the 5’ carbon of deoxyribose – a free hydroxyl group (-OH) at the 3’ carbon of deoxyribose
  10. 10. 18
  11. 11. DNA Structure Nucleotides are connected to each other to form a long chain phosphodiester bond: bond between adjacent nucleotides – formed between the phosphate group of one nucleotide and the 3’ –OH of the next nucleotide The chain of nucleotides has a 5’ to 3’ orientation.
  12. 12. 20
  13. 13. 21 DNA Structure Determining the 3-dimmensional structure of DNA involved the work of a few scientists: – Erwin Chargaff determined that • amount of adenine = amount of thymine • amount of cytosine = amount of guanine This is known as Chargaff’s Rules
  14. 14. Chargaff
  15. 15. DNA Structure Rosalind Franklin and Maurice Wilkins – Franklin performed X-ray diffraction studies to identify the 3-D structure – discovered that DNA is helical – discovered that the molecule has a diameter of 2nm and makes a complete turn of the helix every 3.4 nm
  16. 16. Franklin
  17. 17. 26 DNA Structure James Watson and Francis Crick, 1953 – deduced the structure of DNA using evidence from Chargaff, Franklin, and others – proposed a double helix structure
  18. 18. 28 DNA Structure The double helix consists of: – 2 sugar-phosphate backbones – nitrogenous bases toward the interior of the molecule – bases form hydrogen bonds with complementary bases on the opposite sugar-phosphate backbone
  19. 19. 29
  20. 20. 30 DNA Structure The two strands of nucleotides are antiparallel to each other – one is oriented 5’ to 3’, the other 3’ to 5’ The two strands wrap around each other to create the helical shape of the molecule.
  21. 21. Double Helix • 2 complementary strands of DNA – sugar-phosphate backbone – nitrogenous bases stacked in the center – antiparallel • 5’ end • 3’ end – twists to right
  22. 22. 33
  23. 23. Base Pairing in DNA: The Watson-Crick Model According to the Watson–Crick model, a DNA molecule consists of two polynucleotide strands coiled around each other in a helical, screwlike fashion. The sugar–phosphate backbone is on the outside of this right-handed double helix, and the heterocyclic bases are on the inside, so that a base on one strand points directly toward a base on the second strand. The double helix resembles a twisted ladder, with the sugar–phosphate backbone making up the sides and the hydrogen-bonded base pairs, the rungs.
  24. 24. AT GC TA CG CG GC AT
  25. 25. Chargaff’s Rules • base pairing rules – A=T – C G
  26. 26. Prentice Hall © 2007 Chapter Twenty Six 40 Hydrogen bonds connect the pairs of bases; thymine with adenine, cytosine with guanine.
  27. 27. Structure of DNA
  28. 28. DNA double Helix Chargaff’s rules: the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine, and the total amount of purines equals the total amount of pyrimidine.
  29. 29. Hydrogen bonds between complementary bases FORMAMIDE, ANNEALING
  30. 30. The three helical forms of DNA (and RNA) Physiological DNA Very unusual DNA RNA High-salt DNA
  31. 31. Type Shape Helix Base pair per turn Pitch per bp Width Occurrence A Broadest Right handed 11 0.256 nm 2.3 nm High salt Medium B Intermediat e Right handed 10 0.338 nm 1.9 nm Normal Form Z Elongated Left handed 12 0.571 nm 1.8 nm Some of DNA
  32. 32. B-form DNA consists of a right-handed double helix with antiparallel strands 34 Å (10 bp) per turn major groove minor groove major groove minor 3.4 Å per bp These dimensions are for DNA fibers. In solution, there are ~10.5 base-pairs per turn. 5’ 3’ 5’3’
  33. 33. Pharm201 Lecture 2 2007 50 Canonical A DNA
  34. 34. Pharm201 Lecture 2 2007 51 Z-DNA
  35. 35. Summary of the main structural features of B-form DNA •Right-handed helix •Two antiparallel strands held together by Watson-Crick hydrogen bonds •Pitch (repeat length) = 34 Å (3.4 nm) •36o rotation between residues •Helix diameter of 20 Å (2.0 nm) •Wide major groove, narrow minor groove •Chargaff’s Rules: A = T; G = C •Charged phosphates •Bases in anti configuration •The strands separate at high temperatures •The solution structure is dynamic
  36. 36. DNA • Functions • 1. Storage of genetic information • 2. Self-duplication & inheritance. • 3. Expression of the genetic message. • DNA’s major function is to code for proteins. • Information is encoded in the order of the nitrogenous bases.
  37. 37. Figure 11.6 DNA double helix (2-nm diameter) Metaphase chromosome 700 nm Tight helical fiber (30-nm diameter) Nucleosome (10-nm diameter) Histones “Beads on a string” Supercoil (200-nm diameter) HISTONES H1, H2A, H2B, H3, H4