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Biology LibreTexts

Part 2: DNA Replication

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  • DNA Replication

    Replication is the process where DNA makes a copy of itself. Cells divide for an organism to grow or reproduce; every new cell needs a copy of the DNA or instructions to know how to be a cell. DNA replicates right before a cell divides.

    DNA replication is semi-conservative. That means that when it makes a copy, one half of the old strand is always kept in the new strand. This helps reduce the number of copy errors.


    There are a few enzymes involved in DNA replication: RNA primase adds a short segment of RNA to start the new strand. DNA helicase opens up the double helix by breaking hydrogen bonds that hold complementary strands together. A DNA polymerase adds the new nucleotides onto the 3’ end of the growing strand. DNA ligase connects Okazaki fragments on the lagging strand into a continuous molecule.

    For simplicity’s sake, an RNA primer will not be used during this activity and the action of the laggingstrand will not be modeled.

    1. Assemble a new DNA molecule with the following sequence: 5’ GCAT 3’

                                                                     3’ CGTA 5’

    Make sure that your molecule is laid out on the bench exactly as written!!

    2. Use your hands to mimic the action of DNA helicase (separate the two strands)

    3. Build daughter strands using the original molecule as a template.

    4. Disassemble your DNA molecules