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Biology
Biology
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13-2 Manipulating DNA
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3. The Tools of Molecular Biology
How do scientists make changes to DNA?
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4. The Tools of Molecular Biology
Scientists use different techniques to:
extract DNA from cells
cut DNA into smaller pieces
identify the sequence of bases in a DNA molecule
make unlimited copies of DNA
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5. The Tools of Molecular Biology
In genetic engineering, biologists make changes in the DNA code of a living organism.
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6. The Tools of Molecular Biology
DNA Extraction
DNA can be extracted from most cells by a simple chemical procedure.
The cells are opened and the DNA is separated from the other cell parts.
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7. The Tools of Molecular Biology
Cutting DNA 
Most DNA molecules are too large to be analyzed, so biologists cut them into smaller fragments using restriction enzymes.
Which type of molecule is an enzyme?
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8. The Tools of Molecular Biology
Each restriction enzyme cuts DNA at a specific sequence of nucleotides.
Recognition sequences
DNA sequence
Restriction enzyme EcoR I cuts the DNA into fragments
Molecular biologists have developed different techniques that allow them to study and change DNA molecules. Restriction enzymes cut DNA at specific sequences. This drawing shows how restriction enzymes are used to edit DNA. The restriction enzyme EcoR I, for example, finds the sequence CTTAAG on DNA. Then, the enzyme cuts the molecule at each occurrence of CTTAAG. The cut ends are called sticky ends because they may “stick” to complementary base sequences by means of hydrogen bonds.
Sticky end
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9. The Tools of Molecular Biology
Separating DNA  
In gel electrophoresis, DNA fragments are placed at one end of a porous gel, and an electric voltage is applied to the gel.
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10. The Tools of Molecular Biology
DNA plus restriction enzyme
Power source
Longer fragments
Shorter fragments
Mixture of DNA fragments
Gel
Gel electrophoresis is used to separate DNA fragments. First, restriction enzymes cut DNA into fragments. The DNA fragments are then poured into wells on a gel, which is similar to a thick piece of gelatin. An electric voltage moves the DNA fragments across the gel. Because longer fragments of DNA move through the gel more slowly, they do not migrate as far across the gel as shorter fragments of DNA. Based on size, the DNA fragments make a pattern of bands on the gel. These bands can then be compared with other samples of DNA. 
Gel Electrophoresis
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11. The Tools of Molecular Biology
First, restriction enzymes cut DNA into fragments.
The DNA fragments are poured into wells on a gel.
DNA plus restriction enzyme
Gel electrophoresis is used to separate DNA fragments. First, restriction enzymes cut DNA into fragments. The DNA fragments are then poured into wells on a gel, which is similar to a thick piece of gelatin. An electric voltage moves the DNA fragments across the gel. Because longer fragments of DNA move through the gel more slowly, they do not migrate as far across the gel as shorter fragments of DNA. Based on size, the DNA fragments make a pattern of bands on the gel. These bands can then be compared with other samples of DNA. 
Mixture of DNA fragments
Gel
Gel Electrophoresis
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12. The Tools of Molecular Biology
An electric voltage is applied to the gel.
The smaller the DNA fragment, the faster and farther it will move across the gel.
Power source
Gel electrophoresis is used to separate DNA fragments. First, restriction enzymes cut DNA into fragments. The DNA fragments are then poured into wells on a gel, which is similar to a thick piece of gelatin. An electric voltage moves the DNA fragments across the gel. Because longer fragments of DNA move through the gel more slowly, they do not migrate as far across the gel as shorter fragments of DNA. Based on size, the DNA fragments make a pattern of bands on the gel. These bands can then be compared with other samples of DNA. 
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13. The Tools of Molecular Biology
Power source
Longer fragments
Shorter fragments
Gel electrophoresis is used to separate DNA fragments. First, restriction enzymes cut DNA into fragments. The DNA fragments are then poured into wells on a gel, which is similar to a thick piece of gelatin. An electric voltage moves the DNA fragments across the gel. Because longer fragments of DNA move through the gel more slowly, they do not migrate as far across the gel as shorter fragments of DNA. Based on size, the DNA fragments make a pattern of bands on the gel. These bands can then be compared with other samples of DNA. 
Gel Electrophoresis
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Using the DNA Sequence
Making Copies 
Polymerase chain reaction (PCR) is a technique that allows biologists to make copies of genes.
Small amounts of DNA can be multiplied making it easier to analyze.
Made possible by an enzyme found in a bacterium living in hot springs in Yellow Stone National Park.
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Using the DNA Sequence
Polymerase Chain Reaction (PCR)
DNA heated to separate strands
DNA polymerase adds complementary strand
DNA fragment to be copied
Polymerase chain reaction (PCR) is used to make multiple copies of genes.
PCR cycles 1 2 3 4
5 etc.
DNA copies 1 2 4 8
16 etc.
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13-2
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13-2
Restriction enzymes are used to
extract DNA.
cut DNA.
separate DNA.
replicate DNA.
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13-2
During gel electrophoresis, the smaller the DNA fragment is, the
more slowly it moves.
heavier it is.
more quickly it moves.
darker it stains.
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13-2
The DNA polymerase enzyme found in bacteria living in the hot springs of Yellowstone National Park illustrates
genetic engineering.
the importance of biodiversity to biotechnology.
the polymerase chain reaction.
selective breeding.
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13-2
A particular restriction enzyme is used to
cut up DNA in random locations.
cut DNA at a specific nucleotide sequence.
extract DNA from cells.
separate negatively charged DNA molecules.
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13-2
During gel electrophoresis, DNA fragments become separated because
multiple copies of DNA are made.
recombinant DNA is formed.
DNA molecules are negatively charged.
smaller DNA molecules move faster than larger fragments.
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