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DNA Structure, Function and Replication. B5 – Describe DNA replication: Review DNA structure and function Describe the purpose of DNA replication Identify

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  • DNA Structure, Function and Replication

  • B5 Describe DNA replication:Review DNA structure and functionDescribe the purpose of DNA replicationIdentify the site of DNA replication in a cellDescribe the three steps in DNA replicationExplain why DNA replication in called semi-conservative

  • Comic by Kate Beaton, http://harkavagrant.com/

  • Double helixBackbone is sugar and phosphate joined by covalent bondsRungs are complementary base pairs joined by hydrogen bonds (purine-pyrimidine: A-T, G-C)Note that the nucleotides in the two strands are laid out in opposite directions (antiparallel)

  • DNA carries the genetic codeReplicates to pass on genetic informationInstructions for synthesis of proteins Proteins are required to build an organism and catalyze all of its biochemical reactions (therefore controlling all of the functions of the cell and organism)

  • Questions for discussion:What is meant by the term DNA replication?Why is DNA replication necessary?Where does it take place?When does it take place?What is the function of the genetic code?

  • DNA must be replicated in every cell before the cell dividesThis is necessary so that each new cell has a complete copy of the genetic codeThe method of DNA replication is known as semi-conservative(what do you think this means?)

  • The double-stranded DNA molecule unzips when the enzyme DNA helicase breaks the hydrogen bonds between complementary bases

  • Each strand acts as a template to make new double helixNew complementary nucleotides attach to the exposed basesCatalyzed by the enzyme DNA polymerase

  • Adjacent phosphate and sugar groups are attached by another DNA polymeraseWe now have two DNA molecules, each identical to the original

  • This is called semi-conservative replication because half of each DNA strand is old and the other half is new