Dna model

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Dna model

  1. 1. DNA MODEL
  2. 2. STRUCTURE • deoxyribonucleic acid • two strands of polymer wound into a helix • complementary chains • nucleotides • nitrogenous bases (adenine, cytosine, guanine, thymine) • sugar (deoxyribose) • phosphate group
  3. 3. STRUCTURE • double helix is due to the differences in size of the nitrogenous base • two-ring compound (adenine, guanine) and one-ring compound (cytosine , thymine) • helical structure makes DNA equal in distance • Nitrogenous bases can only fit together if arrange in antiparallel • twisting is right-handed • contains major and minor grooves
  4. 4. DNA Conformations • B – DNA (B form) • observed in high humidity • corresponds to the average structure of the DNA in physiological conditions • 10 base pairs per turn • wide major groove and narrow minor groove • right handed helical • long and thinner
  5. 5. DNA Conformations • A – DNA (A form) • observed in low humidity • some DNA adopts this structure in protein complex • double helix RNA are in A-form • 11 base pairs per turn • narrow and deep major groove and broad and shallow minor groove • right handed helical • short and broad
  6. 6. DNA Conformations • Z – DNA (Z form) • found in solutions containing high concentrations of + charged ions (sodium) • unknown physiological significance but found in cell’s DNA in small portions • 12 base pairs per turn • flattened major groove and extremely narrow and deep minor groove • left handed helical • elongated and slim
  7. 7. DNA Replication • DNA templating • requires separation of the helix • recognition of nucleotides by free complementary nucleotides r • DNA replication fork is asymmetrical • leading strand and a lagging strand • DNA replication starts in origins of replication • recognized by the protein origin recognition complex • DNA contains A and Ts
  8. 8. CENTRAL DOGMAOF MOLECULAR BIOLOGY
  9. 9. DNA Replication
  10. 10. DNA Replication • DNA polymerase – responsible in adding nucleotides during replication • helicase – unwinds the DNA so that DNA polymerase can attach to the template strand and start replication • DNA ligase – responsible in putting together Okazaki fragments
  11. 11. Transcription • DNA strands separated temporarily to produce a formation that allows the insertion of RNA polymerase • RNA polymerase adds complementary nucleotides (A - U and C - G)
  12. 12. Transcription
  13. 13. Transcription • exons (expressed sequences) • RNA splicing • mRNA
  14. 14. Translation • Genetic code • sequence of nucleotides in mRNA is read in consecutive groups of three • RNA is a linear polymer of 4 different nucleotides (A,U,G,C) • if read in groups of three 4 X 4 X 4 = 64 possible combinations of AA 20 different AA are known • the genetic code is redundant and some amino acids are specified by more than one triplet
  15. 15. Translation
  16. 16. Translation

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