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DNA Structure and DNA Replication

DNA Structure and DNA Replication. DNA Structure. DNA stands for D eoxyribo n ucleic A cid Shape: Double helix Monomers: Nucleotides Nucleotide has 3 parts: Sugar (deoxyribose), phosphate, and a nitrogenous base Bases are held together by hydrogen attractions.

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DNA Structure and DNA Replication

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  1. DNA StructureandDNA Replication

  2. DNA Structure • DNA stands for Deoxyribonucleic Acid • Shape: Double helix • Monomers:Nucleotides • Nucleotide has 3 parts: Sugar (deoxyribose), phosphate, and a nitrogenous base • Bases are held together by hydrogen attractions. • Why are hydrogen attractions important in DNA’s structure?

  3. Four Nitrogenous Bases • Adenine (A), Guanine (G), Cytosine (C), Thymine (T) • Purines (double ring) – Adenine and Guanine • Pyrimidines (single ring) – Cytosine and Thymine • Chargaff’s rule: • Adenine pairs with thymine. A –T T – A • Guanine pairs with cytosine. G – C C – G

  4. Nucleotides: Page 291 Purines Pyrimidines Adenine Guanine Thymine Cytosine Phosphate group Sugar: Deoxyribose

  5. So if every living thing has the same 4 bases, how are we so different? • It’s the SEQUENCE!! The order of those 4 nitrogen bases determines whether you are a human or a dog! • It also determines traits of that organism (why you look different than your neighbor.)

  6. A Closer Look at DNA: Page 294 Nucleotide Hydrogen bonds Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

  7. A closer look at DNA:How DNA condenses DNA double helix Chromosome Centromere Supercoils Histones Chromatin

  8. What is DNA Replication? The process of making copies of DNA during S phase of interphase in the nucleus Makes sure that a daughter cell will have a complete set of chromosomes Original strand of DNA serves as a template for 2 new strands Template: a pattern; an original model Each new strand will be identical to the original strand because of Chargaff’s rule.

  9. How does DNA replication work? • 1) Helicase unwinds the double helix, forming a “replication fork,” where replication takes place • 2) DNA polymerase bonds the necessary nucleotides to the original DNA strand to complete 2 new DNA molecules • 3) DNA polymerase also “proofreads” the new DNA strand to make sure it is an exact copy of the original DNA

  10. DNA Replication Facts: • DNA polymerase can only work in one direction so: • 2 new strands of DNA are made in opposite directions • One strand is made in sequence of nucleotides • The other strand is what we call the “lagging strand” because nucleotides are added in fragments

  11. DNAhttp://www.youtube.com/watch?v=z685FFqmrpo Original strand DNA polymerase New strand Growth DNA polymerase Growth Replication fork Replication fork Nitrogenous bases New strand Original strand

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