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Intro to DNA

Intro to DNA

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Intro to DNA

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  1. Intro to DNA DNA = Deoxyribonucleic acid -double polymer of nucleotides -SS chromosomes contain 1 molecule of DNA (re: double polymer of nuc’s) -after DNA replication, a DS chromosome contains 2 complete polymers of DNA -sequence of nucleotides of DNA codes for sequence of amino acids of protein (process referred to as protein synthesis) -protein synthesis = DNA  RNA  Protein - The pathway of protein synthesis is also referred to as the Central Dogma of Molecular Biology

  2. DNA is a polymer of nucleotides • A nucleotide contains three essential parts: • 5 carbon sugar • Deoxyribose in DNA • Ribose in RNA • Nitrogenous base • Adenine, Guanine = purines • Thymine, (Uracil), Cytosine = pyrimidines • Phosphate group

  3. Components of nucleotide structure

  4. Single polymer of DNA nucleotides

  5. Events leading to DNA model proposed by Watson and Crick (1953) • Chargaff’s rules: • the proportion of A’s in DNA = the proportion of T’s • The same holds true for G’s and C’s • Franklin’s X-ray diffraction photos: • Suggested DNA was helical and perhaps contained two separate chains of nucleotides separated by a discrete diameter • Watson/Crick model fit the available data: • Each “backbone” of alternating sugar – phosphate • Each backbone has a polarity in that each is oriented in the opposite direction • Complementary base pairing between purine and pyrimidine: • A binds to T (forming 2 H bonds) • G binds with C (forming 3 H bonds) • Model suggested a mechanism of DNA replication and of protein synthesis

  6. DNA structure with double polymer of DNA nucleotides showing antiparallel orientation of complementary nucleotide strands

  7. Basics of DNA replication:replication is via semi-conservative model

  8. Basics of DNA replication • The DNA helix “unzips” exposing the 2 single-stranded parental templates of nucleotides • New nucleotides are added against each exposed nucleotide in a complementary fashion • Since the enzyme which completes this task “reads” the DNA in only 1 direction, it affects the process of DNA replication

  9. The replication process:

  10. The replication process:

  11. The replication process:

  12. Replication process with major enzymes included

  13. Replication of lagging strand