Se ha denunciado esta presentación.
Se está descargando tu SlideShare. ×
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Próximo SlideShare
DNA TOPOLOGY
DNA TOPOLOGY
Cargando en…3
×

Eche un vistazo a continuación

1 de 25 Anuncio
Anuncio

Más Contenido Relacionado

Presentaciones para usted (20)

Similares a Dna topology (20)

Anuncio

Más reciente (20)

Dna topology

  1. 1. DNA TOPOLOGY ALICIA TINY St. Mary's college ,Thrissur
  2. 2. Content STRUCTURE OF DNA DIFFERENT FORMS OF DNA TOPOLOGY
  3. 3. Structure of DNA has been studied by many people for many years Linus Pauling Maurice Wilkin and Rosalind Franklin James Watson and Francis Crick
  4. 4. STRUCTURE OF DNA • The structure of DNA is divided into four different levels • Primary • Secondary • Tertiary • Quantanary
  5. 5. • Primary structure consists of a linear sequence of nucleotides that are linked together by phosphodiester bonds It is this linear sequence of nucleotides that make up the Primary structure of DNA or RNA. • Secondary structure is the set of interactions between bases, i.e., which parts of strands are bound to each other. In DNA double helix, the two strands of DNA are held together by hydrogen bonds.
  6. 6. • Secondary structure is the set of interactions between bases, i.e., which parts of strands are bound to each other. In DNA double helix, the two strands of DNA are held together by hydrogen bonds. 6
  7. 7. • Tertiary structure refers to the locations of the atoms in three-dimensional space, It is a higher order than the secondary structure, in which large-scale folding in a linear polymer occurs and the entire chain is folded into a specific 3-dimensional shape. • There are 4 areas in which the structural forms of DNA can differ. • Handedness – right or left • Length of the helix turn • Number of base pairs per turn • Difference in size between the major and minor grooves
  8. 8. • The quaternary structure of nucleic acids is similar to that of protein quaternary structure. • The quaternary structure refers to a higher-level of organization of nucleic acids. 8
  9. 9. PowerPlugs Templates for PowerPoint Preview 9
  10. 10. Watson and Crick model DNA is a double stranded helix The X-ray diffraction helped to identify that DNA was helical. Watson and Crick performed no experiment themselves there tactic was to use other groups data to build DNA model. Postulates of Watson and Crick model……
  11. 11. Different forms of DNA DNA the genetic information crrier can have different structural conformations they are A-DNA B-DNA C-DNA Z-DNA PowerPlugs Templates for PowerPoint Preview 12
  12. 12. A-DNA • A DNA is of a rare type of structural conformation DNA can adopt under dehydrated conditions this apparently protects DNA under conditions such as the extreme desiccation of bacteria. • Its double stranded similar to B DNA but shorter and more compact • Much wider than B DNA • The helix diameter of A-DNA is 26 • The conformation of gycosidic bond in A-DNA is anti form • Major grove is narrow and deep • Minor groove is broad and shallow • A-DNA has a axial hole in the center 13
  13. 13. B DNA • Discovered by Watson and Crick • It is most common and predominant form of DNA • Its double stranded • B-DNA has a solid central core • The major groove is wide and deep • Minor groove is narrow and deep • Gycosidic bond is it anti form conformation 14
  14. 14. Z DNA • Z-DNA is one of the many possible double helical structures of DNA. It is a left-handed double helical structure in which the helix winds to the left in a zigzag pattern (instead of to the right, like the more common B-DNA form). • Left-handed DNA was first discovered by Robert Wells and colleagues • It has a flat major groove • Minor groove is narrow and deep • Gycocidic bond is anti for pyrimidines and syn- purines 15
  15. 15. C DNA • C-DNA also known as C form DNA. It is one of the many possible double helical structures of DNA. This form of DNA can be observed at some conditions such as relatively low humidity and the presence of certain ions, such as Li+ or Mg2+. • Its shape is narrow 16
  16. 16. 17
  17. 17. Topology • Topology is only defined that for a continuous strand • Topological aspect of DNA structure arises primarily from the fact that the two DNA strands are repeatedly intertwined • A DNA segment constrained in such a way that it ends cannot rotate freely is called a topological domain. 18
  18. 18. PowerPlugs Templates for PowerPoint Preview 19
  19. 19. DNA in its relaxed state usually assumes the B configuration . • It has the minimum energy and deviation • Any deviation can cause a change in the energy level • In prokaryotes, DNA is always circular and so this circularity leads to a lot of different properties of DNA, it leads to the notion of DNA topology. 20
  20. 20. • DNA is said to be topologically constrained because of their length, entertainment in chromatin, interaction with other cellular components. • The number of times one strand would have to be passed through the other strand in order for the 2 strands to entirely separate from each other is called linking number. It is always an integer. Linking number is the sum of two geometric components called twist and writh. • L=W+T AND dL=dw+dT • Twist(T) is number of helical turns of one DNA about another • Wrist (W) a property of super coiled molecules, is the number of turns of the axis of the double stranded helix is space . 21
  21. 21. PowerPlugs Templates for PowerPoint Preview 22
  22. 22. There are special enzymes called topoisomerases, which change DNA topology. They are present in eukaryotes and prokaryotes . If you shut down or silence the genes of topoisomerases in eukaryotes, all major processes, such as replication and transcription, in the cell will stall. 23
  23. 23. CONCLUSION • DNA is the source of genetic information in most living organisms. • It has different structures and different conformational structures 24
  24. 24. 25

×