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Manipulating DNA
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Scientists use knowledge of the structure and function of DNA to manipulate it.
The Tools of Molecular Biology
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The Tools of Molecular Biology
Techniques:
• extract DNA from cells
• cut it into smaller pieces
• identify the sequence of bases in it
• make unlimited copies of it
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The Tools of Molecular Biology
DNA Extraction
The cells are broken open and the DNA is separated from the other molecules.
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The Tools of Molecular Biology
Cutting DNA
DNA is cut into smaller fragments using restriction enzymes.
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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
Sticky end
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The Tools of Molecular Biology
Separating DNA - gel electrophoresis
DNA fragments are placed at one end of a porous gel and an electric voltage is applied.
The negatively-charged DNA molecules move toward the positive end of the gel.
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The Tools of Molecular Biology
DNA plus restriction enzyme
Mixture of DNA fragments
Gel
Power source
Gel Electrophoresis
Longer fragments
Shorter fragments
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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
Mixture of DNA fragments
Gel
Gel Electrophoresis
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The Tools of Molecular Biology
An electric voltage is applied to the gel.
DNA fragments move across the gel.
Smaller fragments move faster and farther.
Power source
Gel Electrophoresis
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The Tools of Molecular Biology
DNA fragments make a pattern of bands.
These bands can then be compared with other samples of DNA.
Longer fragments
Shorter fragments
Gel Electrophoresis
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Using the DNA Sequence
Cutting and Pasting
Enzymes that splice DNA together make it possible to take a gene from one organism and attach it to the DNA of another.
Such DNA molecules are called Recombinant DNA.
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Using the DNA Sequence
Making Copies
Polymerase chain reaction (PCR) allows biologists to make copies of genes.
-DNA is heated to separate its two strands.
-Primers bind to the single-stranded DNA.
-DNA polymerase makes copies of the DNA
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Using the DNA Sequence
DNA heated to separate strands
PCR cyclesDNA copies
1 2 3 4 5 etc.1 2 4 8 16 etc.
Polymerase Chain Reaction (PCR)
DNA polymerase adds complementary strand
DNA fragment to be copied
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Cell TransformationRecombinant DNA
Host Cell DNA
Target gene
Modified Host Cell DNA
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Transforming Bacteria
Transforming Bacteria
A cell takes in DNA from outside the cell.
Foreign DNA is first joined to a small, circular DNA molecule in bacteria known as a plasmid.
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Transforming Bacteria
Recombinant DNA
Gene for human growth hormone
Gene for human growth hormone
Human Cell
Bacteria cell
Bacterial chromosome
Plasmid
Sticky ends
DNA recombination
Bacteria cell containing gene for human growth hormone
DNA insertion
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Transforming Plant Cells
Transforming Plant Cells
• A bacterium exists that produces tumors in plants.
• Researchers can inactivate the tumor gene and insert a piece of foreign DNA into the plasmid.
• The recombinant plasmid can then be used to infect plant cells.
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Transforming Plant Cells
Complete plant generated from transformed cell.
Inside plant cell, Agrobacterium inserts part of its DNA into host cell chromosome.
Plant cell colonies
Transformed bacteria introduce plasmids into plant cells.
Agrobacterium tumefaciens
Cellular DNA
Gene to be transferred
Recombinant plasmid
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Transforming Animal Cells
Transforming Animal Cells
• DNA can be directly injected into the nucleus of an egg cell.
• Enzymes insert the foreign DNA into the chromosomes of the injected cell.
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Transforming Animal Cells
Recombinant DNA
Modified Host Cell DNA
Target gene
Flanking sequences match host
Recombinant DNA replaces target gene
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Applications of Biotechnology
Transgenic Organisms
• Contains genes from other species.
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Transgenic Organisms
Transgenic Microorganisms
• Transgenic bacteria produce important substances useful for health and industry.
• insulin
• growth hormone
• clotting factor
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Transgenic Organisms
Transgenic Animals
• Transgenic animals have been used to improve the food supply.
• Mice have been produced with human genes that make their immune systems act similarly to ours.
• This allows scientists to study the effects of diseases on the human immune system.
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Transgenic Organisms
Transgenic Plants
• Transgenic plants are now an important part of our food supply.
• Many of these plants contain a gene that produces a natural insecticide, so plants don’t have to be sprayed with pesticides.
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Cloning
Cloning
• A clone is a member of a population of genetically identical cells produced from a single cell.
• In 1997, Ian Wilmut cloned a sheep called Dolly.
Dolly and Bonnie
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Cloning
Cloning Dolly
Donor Nucleus
Fused cell
Embryo
Egg Cell
Foster MotherCloned Lamb
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Cloning
Cloning Dolly
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Cloning
Cloning Dolly
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Cloning
Cloning Dolly
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Cloning
Cloning Dolly
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Cloning
Cloning Dolly
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Cloning
Cloning Dolly
