Intro to dna
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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

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Intro to DNA

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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


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


Components of nucleotide structure


Single polymer of DNA nucleotides


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


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


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


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


The replication process:


The replication process:


The replication process:


Replication process with major enzymes included


Replication of lagging strand


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