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DNA Replication

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DNA Replication AP Biology Unit 3 Hershey & Chase Experiment Bacteriophages are viruses that infect bacteria Bacteriophages consist of DNA and protein (capsid) What ... – PowerPoint PPT presentation

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Title: DNA Replication


1
DNA Replication
AP Biology Unit 3
2
Hershey Chase Experiment
  • Bacteriophages are viruses that infect bacteria
  • Bacteriophages consist of DNA and protein
    (capsid)
  • What part of the bacteriophage holds the
    instructions of how to make more viruses?
  • DNA

3
Hershey Chase determined that DNA is the
genetic material
4
DNA Structure
  • Double Helix (2 strands of DNA)
  • Complementary strands pair up (A T, C G)
    hydrogen bonds
  • Strands are antiparallel (5 and 3 ends)

5
DNA Replication
  • When DNA is copied during S Phase of Interphase
  • Basic Concept create a new strand by matching
    nucleotides to an existing strand

6
DNA Replication
  • Replication is semi-conservative (one strand is
    old, one strand new)

7
Origins of Replication
  • Where DNA Replication starts
  • Differs between organisms
  • Prokaryotes 1 origin of replication
  • Eukaryotes many different origins of
    replication

8
General Process of DNA Replication
  • Step 1 Initiator Proteins bind to origins of
    replication to begin replication
  • Attracts other enzymes involved in replication
    process

9
General Process
  • Step 2
  • DNA Helicase separates the DNA helix
  • Topoisomerase (Gyrase) prevents overwinding of
    DNA
  • Single Stranded Binding Proteins (SSBs) prevent
    double helix from reforming temporarily

10
Question
  • What kind of bonds does Helicase break?
  • Hydrogen bonds

11
General Process
  • Step 3 Primase builds an RNA primer at the
    starting from the 5 end of the new DNA strand
  • Uses the 3 end of existing DNA strand
  • Why? Because the DNA Polymerase III (main DNA
    building enzyme) needs something to build off of

12
General Process
  • Step 4 DNA Polymerase III builds the new strand
    of DNA in a 5 to 3 direction
  • What kinds bonds are being formed to make a new
    strand of DNA?
  • Covalent bonds

13
Question
  • What other enzyme builds similarly to DNA
    Polymerase III?
  • RNA Polymerase (dont mix it up with DNA
    Polymerase III!)

14
Problem
  • How can both strands of DNA be replicated in a
    5- 3 direction at the same time they are
    antiparallel?
  • Answer leading and lagging strands

15
Leading and Lagging Strands
  • Leading strand is synthesized continuously in the
    direction of replication (goes in the same
    direction as helicase)
  • Lagging strand is synthesized in short fragments
    the opposite direction of replication (opposite
    direction as helicase)

16
Questions
  • How many primers does the leading strand need?
  • Only 1 to start replication
  • How many primers does the lagging strand need?
  • Many one for each Okazaki fragment

17
Lagging Strand
18
DNA Ligase
  • DNA Ligase seals Okazaki fragments together
  • Forms covalent bonds between nucleotides to
    create a continuous strand of DNA

19
Finishing DNA Replication
  • Problem 1 There are still RNA nucleotides in
    the DNA (primers)
  • Solution DNA Polymerase I cuts out the RNA
    nucleotides and replaces them with DNA

20
Finishing DNA Replication
  • Problem 2 Okazaki fragments and bases replaced
    DNA Polymerase I are not attached to rest of DNA
  • Solution DNA Ligase seals everything together

21
Putting It All Together
  • Label the diagram on Page 67 with the following
    terms
  • SSBs - DNA Ligase
  • Leading Strand - Lagging Strand
  • Helicase - Primase
  • DNA Polymerase III - Primer
  • DNA Polymerase I

22
SSBs
DNA Polymerase III
Helicase
Leading Strand
DNA Ligase
DNA Polymerase I
DNA Pol III
Primase
Lagging Strand
Primer
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