Nucleic Acid Chemistry

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Central Dogma

• M.Prasad Naidu
• MSc Medical Biochemistry, Ph.D,.

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Central Dogma

• DNA ----------------? RNA--------------?
  protein

Replication
transcription
translation
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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

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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

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Replica

• Write the strand complementary to
• 3 ACTAGCCTAAGTCG 5
• Answer

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Replication is Semiconservative
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Replication

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

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Replication
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Replication

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

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Replication
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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

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Replication
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Replication

• Lagging strand
• 5 end of template
• Cant be made continuously as direction is wrong
• RNA primer
• New DNA made 5 ? 3
• Opposite direction of replication
• Discontinuous
• Okazaki fragments
• Ligase closes gaps

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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

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Transcription

• From following DNA strand, determine RNA sequence
• 3 GCCTAAGCTCA 5
• Answer

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Transcription
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Transcription

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

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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

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Introns and Exons

• Introns
• Intervening sequences
• Not all DNA codes for protein
• Regulatory info, junk DNA
• Exons
• Code for protein

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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

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Processing of hnRNA into mRNA
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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

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