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NUCLEIC ACIDS

BIOCHEMISTRY

mprasadnaidu
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NUCLEIC ACIDS

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  1. M.Prasad Naidu MSc Medical Biochemistry, Ph.D,. Central Dogma

  2. Central Dogma DNA ---------------- RNA-------------- protein Replication transcription translation

  3. Central Dogma • Replication • DNA making a copy of itself • Making a replica • Transcription • DNA being made into RNA • Still in nucleotide language • Translation • RNA being made into protein • Change to amino acid language

  4. Replication • Remember that DNA is self complementary • Replication is semiconservative • One strand goes to next generation • Other is new • Each strand is a template for the other • If one strand is 5’ AGCT 3’ • Other is: 3’ TCGA 5’

  5. Replica • Write the strand complementary to: 3’ ACTAGCCTAAGTCG 5’ Answer

  6. Replication is Semiconservative

  7. Replication • Roles of enzymes • Topoisomerases • Helicase • DNA polymerases • ligase • DNA binding proteins • DNA synthesis • Leading strand • Lagging strand

  8. Replication

  9. Replication • Helix opens • Helicase • Causes supercoiling upstream • Topoisomerases (gyrase) • DNA Binding Proteins • Prevent reannealing

  10. Replication

  11. Replication • Leading strand • 3’ end of template • As opens up, DNA polymerase binds • Makes new DNA 5’ - 3’ • Same direction as opening of helix • Made continuously

  12. Replication

  13. Replication • Lagging strand • 5’ end of template • Can’t be made continuously as direction is wrong • RNA primer • New DNA made 5’  3’ • Opposite direction of replication • Discontinuous • Okazaki fragments • Ligase closes gaps

  14. Transcription • DNA template made into RNA copy • Uracil instead of Thymine • One DNA strand is template • Sense strand • Other is just for replication • Antisense • In nucleus • nucleoli

  15. Transcription • From following DNA strand, determine RNA sequence 3’ GCCTAAGCTCA 5’ Answer

  16. Transcription

  17. Transcription • DNA opens up • Enzymes? • RNA polymerase binds • Which strand? • Using DNA template, makes RNA • 5’-3’ • Raw transcript called hnRNA

  18. Transcription How does RNA polymerase know where to start? upstream promotor sequences Pribnow Box TATA box RNA polymerase starts transcription X nucleotides downstream of TATA box

  19. Introns and Exons • Introns • Intervening sequences • Not all DNA codes for protein • Regulatory info, “junk DNA” • Exons • Code for protein

  20. Processing of hnRNA into mRNA • 3 steps • Introns removed • Self splicing • 5’ methyl guanosine cap added • Poly A tail added • Moved to cytosol for translation

  21. Processing of hnRNA into mRNA

  22. Translation • RNA -- Protein • Change from nucleotide language to amino acid language • On ribosomes • Vectorial nature preserved • 5’ end of mRNA becomes amino terminus of protein • Translation depends on genetic code

  23. THANK YOU

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