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DNA Review

DNA Review. What does DNA store that is important? If a DNA strand read 3’ AGT-CCG-GTA 5’ what would the complementary strand read? What holds the nitrogen bases together? What are the 3 components of a nucleotide?. Genetic information in its sequence of nitrogen bases. 5’ TCA-GGC-CAT 3’.

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DNA Review

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  1. DNA Review • What does DNA store that is important? • If a DNA strand read 3’ AGT-CCG-GTA 5’ what would the complementary strand read? • What holds the nitrogen bases together? • What are the 3 components of a nucleotide? Genetic information in its sequence of nitrogen bases 5’ TCA-GGC-CAT 3’ Hydrogen bonds Sugar, phosphate group, and nitrogen base

  2. DNA Replication • DNA replication- the process of making a copy of DNA 1 DNA molecule  2 identical DNA molecules • Why is this important? • cells need to copy their DNA before the cells divide in mitosis (growth, repair, and maintenance) • Where does DNA replication occur? • in the nucleus (because DNA is found in the nucleus in eukaryotic cells)

  3. DNA Replication Summary of what we will learn There are three steps to DNA replication: 1) helicase unwinds the double helix opens the strand by breaking the hydrogen bonds between the bases 2) DNA polymerases add nucleotides in a 5’ to 3’ direction, moving TOWARD the replication fork 3) DNA polymerases detach once replication is complete and you end with 2 identical molecules of DNA, each made of one old strand and one new strand

  4. DNA Replication Step 1: • the double helix must unwind before replication can begin. • then the DNA “unzips” • DNA helicase is an enzyme that opens the double helix by breaking the hydrogen bonds that hold the complementary bases together (think of a zipper) • enzymes end in (-ase)

  5. DNA Replication Step 1 con’t: • once separated, additional proteins hold the strands apart • the place where the double helix splits is called the replication fork(it’s Y-shaped)

  6. DNA Replication Step 2: • at the replication fork, enzymes called DNA polymerases move along each of the DNA strands • DNA polymerases add nucleotides to the 3’ end exposed bases according to the base pairing rules

  7. DNA Replication • The overall direction of adding nucleotides is toward the replication fork • goes from 5’ to 3’

  8. DNA Replication Step 3: • step 2 continues until all DNA has been copied and the polymerases detach • produces 2 DNA molecules that are identical to each other

  9. DNA Replication • is semiconservative • semi – half • conserve – to save

  10. DNA Replication • Semiconservative: • This means that every double stranded molecule of DNA has one strand that is from the “old” DNA and one strand is “new”

  11. Summary • DNA unwinds & unzips using helicase • DNA polymerases add nucleotides to the 3’ end of the strands, moving toward the replication fork (5’  3’) • 2 new strands of DNA are made that are identical to the original strands and to each other • The process is semiconservative

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