Do Now!! 
 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.
Replication video!
 https://www.youtube.com/watch?v=5qSrmeiWsuc
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
Do Now!! 
What are the four enzymes involved in DNA
replication? What are their roles?
Why do we say DNA performs semiconservative replication?
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
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!!!!!
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
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 Replication
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.
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
Do Now!! 
 Label the DNA Replication Diagram
7
1
6
2
5
3
4
Replication Animations!!
 http://highered.mheducation.com/sites/0072943696/s
tudent_view0/chapter3/animation__dna_replication_
_quiz_1_.html
Do Now!  (P. 2 and 6)
 What are the four enzymes involved in DNA
replication?
 What specifically do they do?
 What are Okazaki fragments?
Objectives
 To identify the stages of DNA replication
 To define mutations in genes
 To complete a DNA replication worksheet
Do Now!! 
 What are the four enzymes involved in DNA
replication? What specifically do they do?
 What is the difference between the leading and
lagging strand?
 What are Okazaki fragments?
Objectives
 To complete the steps of DNA replication
 To define mutation
 To practice the steps of DNA replication by
completing a lab activity
Do Now!  (P.1)
 What are the four enzymes involved in DNA
replication?
 What specifically do they do?
 What are Okazaki fragments?
Objectives
 To complete the stages of DNA replication
 To label a DNA replication diagram
 To compare and contrast DNA and RNA