Do Now!!  Why must DNA be replicated?  Where do you think replication takes place?  Are mistakes ever made while replicating DNA?  Why must DNA be replicated?  Where do you think replication takes place?  Are mistakes ever made while replicating DNA?

DNA Replication!

Objectives  Explain what replication is and why it must occur in our bodies.  List the different enzymes involved in each step of replication and what they do.  Compare and contrast leading vs. lagging strands.  Explain what replication is and why it must occur in our bodies.  List the different enzymes involved in each step of replication and what they do.  Compare and contrast leading vs. lagging strands.

Replication video!  

Semiconservative Replication o Parental strands of DNA separate o Each strand serves as template o DNA molecules produced have one strand of parental DNA (old) and one daughter strand (new): o “semi”- half o “conserve”- save

Enzymes involved  Helicase- unzips the DNA strand  Primase- adds RNA Primer (tells the next enzyme where to begin!)  DNA polymerase- adds new nucleotides  DNA ligase- links together fragments

Steps to DNA Replication 1. Unwinding  DNA helicase (enzyme) unwinds and unzips the DNA – breaking the hydrogen bonds between the strands  Single-stranded binding proteins (SSB)- go to DNA strand to keep them separated during replication.  RNA primase adds a short segment of RNA, called an RNA primer, on each DNA strand.

1. Unwinding (cont.) DNA unwinds at different spots (Origins) At the replication fork, an enzyme (Helicase) breaks the hydrogen bonds between the bases DNA unwinds at different spots (Origins) At the replication fork, an enzyme (Helicase) breaks the hydrogen bonds between the bases

Steps to DNA Replication (cont.) 2. Base Pairing  DNA polymerase (enzyme) adds complementary nucleotides to parent DNA strand  Only adds in the 5’ to 3’ direction!!!!!  DNA polymerase (enzyme) adds complementary nucleotides to parent DNA strand  Only adds in the 5’ to 3’ direction!!!!!

2. Base Pairing (cont.)  Two daughter strands of DNA are made differently  Leading Strand- Elongated as the DNA unwinds.  Built continuously without breaks  Lagging Strand- Elongates AWAY from replication fork.  Built discontinuously  makes several small fragments of DNA called Okazaki Fragments  Two daughter strands of DNA are made differently  Leading Strand- Elongated as the DNA unwinds.  Built continuously without breaks  Lagging Strand- Elongates AWAY from replication fork.  Built discontinuously  makes several small fragments of DNA called Okazaki Fragments

Okazaki fragments

Steps to DNA Replication (cont.) 3. Joining  DNA Polymerase removes RNA Primer and fills its place with DNA nucleotides  DNA ligase links the Okazaki Fragments.  DNA Polymerase removes RNA Primer and fills its place with DNA nucleotides  DNA ligase links the Okazaki Fragments.

DNA Replication

Mistakes in DNA  DNA replication takes a lot of energy  During replication, mistakes are made (mutations)  Enzymes “proof read” and repair the mistakes:  Ex: DNA polymerase, exonuclease

Eukaryotes vs. Prokaryotes  Eukaryotic DNA unwinds in multiple areas as DNA is replicated.  In prokaryotes, the circular DNA strand is opened at one origin of replication.  Eukaryotic DNA unwinds in multiple areas as DNA is replicated.  In prokaryotes, the circular DNA strand is opened at one origin of replication.

Do Now  Label the DNA Replication Diagram

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