DNA Structure and Replication

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  1. Sounds complicated, but to put it in a nutshell… The blueprint for you! DNA Deoxyribonucleic Acid
  2. 2. And now for a trip down memory lane…  DNA is a macromolecule (Remember that word? Carbohydrates, Lipids, and Proteins ring a bell?)  Type of macromolecule= nucleic acid  Nucleic acid is a polymer built from monomers called nucleotides  4 types of nucleotides make up DNA. Oh, but here’s the catch, there are 3 parts to each nucleotide. Part 1 Part 2 Part 3
  3. 3. The Four Types of Nucleotides  Nucleotides differ in their bases (fancy name= nitrogenous bases)  The bases are:  Thymine (T)  Cytosine (C)  Adenine (A)  Guanine (G)  The nucleotides pair together in something called complementary base pairs… More to come on this later.
  4. 4. DNA Strands Sugar-phosphate backbone  Strands held together by covalent bonds  Sugar of one nucleotide to the phosphate group of another  The bases are lined up along this backbone Sugar Phosphate Base
  5. 5. Now you give it a whirl. •Make one strand of DNA using any of the 4 puzzle pieces on the table. •We will use the other pieces in a minute.
  6. 6. Complementary Base Pairs  The bases of one strand pair up with bases of another strand.  The pairing is caused by hydrogen bonds  There are specific “rules” for the pairing  A pairs with T  G pairs with C
  7. 7. Now you give it a whirl. •Use the remaining puzzle pieces to match four more sets of base pairs together •Check with your neighbor to make sure you have matched correctly.
  8. 8. The Double Helix Watson (left) and Crick  Due to DNA’s unique chemical properties the two stands look like a ladder.  The ladder twists though giving it the double helix shape.
  9. 9. •What type of macromolecule is DNA? •What are the monomers that make up this polymer? •What are the three parts to this monomer? •What are the names of the nitrogenous bases? Let’s Recap Turn to your partner and discuss the answers to these questions.
  10. 10. DNA Replication  Prior to cell division DNA has to make a copy of itself= DNA Replication  Follows a template mechanism for this process much like a photograph is made from a photo negative.  More than a dozen enzymes are involved in the process.  It is fast and amazingly accurate- errors occurring in only about one of a billion nucleotides. Original strand Replicated strand 1 Replicated strand 2
  11. 11. Steps Involved in DNA Replication 1. Two strands of the double helix separate a. This takes place at sites called origins of replication b. The copying proceeds outward in both directions creating replication bubbles. 2. Each single strand acts as a “negative” for producing a new complementary strand. 3. Nucleotides line up one at a time across from the existing strand as predicted by the base pairing rules. 4. Enzymes (DNA polymerases) link the nucleotides covalently to form new DNA strands.
  12. 12. More on DNA replication • Eventually these replication bubble merge, yielding two double-stranded DNA molecules. • In eukaryotes there are many origins of replication allowing the time to copy all of the DNA to be much shorter.
  13. 13. Lets Watch this Happen http://www.johnkyrk.com/DNAreplication.html
  14. 14. Now you give it a whirl. •Refer to the DNA model you made earlier •Make a replication bubble in the middle •These would be consider the original strands. •Now discuss with your shoulder partner what the new strands will look like? How many new DNA molecules will you have and what are they composed of? •Tape/glue the original DNA model that you
  15. 15. •Why does DNA replicate? •When does DNA replicate? •How does DNA replicate? Final Recap Turn to your partner and discuss the answers to these questions.
  16. 16. Time to Write Write down the answer to these questions next to your DNA model. • Why does DNA replicate? • When does DNA replicate? • How does DNA replicate?
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