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The Story of Our DNA.

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The Story of Our DNA. Chapter 11, Section 1 Notes Important Discoveries: DNA s Function Frederick Griffith (1928) Transformation -Turned non-lethal bacteria ... – PowerPoint PPT presentation

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Title: The Story of Our DNA.


1
The Story of Our DNA.
  • Chapter 11, Section 1 Notes

2
Important Discoveries DNAs Function
  • Frederick Griffith (1928) Transformation
  • -Turned non-lethal bacteria into lethal
  • -Hypothesized that a gene was responsible (He did
    NOT know what biomolecule genes were made of)

3
Avery (1944)
  • DNA is the molecule responsible for heredity
  • a. Treated an extract from the heat-killed
    bacteria with enzymes to destroy everything
    except the nucleic acid.
  • Resulted in an identical outcome to Griffiths
    experiment

4
Hershey-Chase (1952)
  • -Studied bacteriophages
  • -Determined that the DNA not the protein coat was
    the source of genetic information

5
Now that scientists agree that DNA carries the
information
  • How is DNA organized?

6
Chargraff (1950)
  • Determined that nucleotides (the building
    blocks of DNA) occur in specific ratios
  • - Guanine cytosine
  • - Adenine thymine
  • Did not know why this was true, only that every
    organism followed this rule

7
Franklin (1950s)
  • - Used x-ray diffraction
  • - Three important pieces of information
  • 1) Each strand is coiled (helix)
  • 2) Two strands of in the structure
  • 3) The nitrogen bases are near the center

8
Watson and Crick (1953)
  • - Used Franklins experiment to determine the 3D
    structure of DNA
  • -The double helix explained both how DNA could
    carry information and how that information could
    be copied
  • - Their model explained why AT and CG

9
What we know now about the structure of DNA
  • Double helix
  • Made of a phosphate backbone
  • Rungs are the nucleotide bases
  • Bases attach in certain patterns
  • C ? G
  • A ? T
  • One side is called the 3 side the other is
    called 5
  • On the ends of the chromosomes in eukaryotes are
    structures called telomeres that are repeating
    bases that protect the DNA

10
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11
DNA Replication
  • The process of duplicating DNA

12
Commonalities in all organisms
  • One side of the double helix gives the
    instructions for the other
  • DNA replication occurs in both directions
  • The site where DNA separation and duplication
    occurs is called a fork

13
Prokaryotes
  • More simple
  • DNA is not in nucleus
  • Plasmid single, circular DNA molecule
  • Much less DNA than a eukaryote
  • DNA replication begins at a single point

14
Eukaryotes
  • DNA is more complex
  • DNA is in a membrane-bound nucleus
  • DNA is wrapped tightly around proteins to form
    chromosomes
  • More DNA than prokaryotes
  • DNA replication occurs at hundreds of points

15
How Replication Occurs
  • Step 1 DNA is opened
  • DNA Helicase reduces the strain caused by the
    unwinding of the DNA

16
Step 2 New DNA is formed
  • DNA Polymerase Helps the daughter strand form
    by matching base pairs
  • Also proofreads the DNA and corrects mistakes
  • Complimentary base pairs are attached to each
    side of the now single-sided DNA
  • Each strand acts as a template
  • New strands of DNA are ½ new and ½ original
  • DNA has a north and south they are called
    5 and 3
  • Base pairs are copied following the 3 to the 5
    direction of the parent strand

17
  • Leading strand the side of the DNA that is
    replicated faster follows the 3 ? 5 of the
    parent strand
  • Lagging strand It is replicated more slowly
  • Okazaki fragment the pieces that are formed in
    the lagging strand, because replication can only
    occur in the 3 to 5 direction as the DNA is
    unwound.

18
Step 3 The pieces of DNA are connected
  • DNA ligase attaches the Okazaki fragments
    together
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