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Manipulating DNA
Manipulating DNA
• Scientists use their knowledge of the
structure of DNA and its chemical
properties to study and change DNA
molecules
• Different techniques are used to study and
change DNA molecules
Tools of Molecular Biology
• Genetic Engineering – making changes in the
DNA code of a living organism
• DNA extraction
• Cells opened to separate DNA from other cell
parts
• Cutting DNA
– DNA too large to study, so biologists “cut” them into
smaller fragments using restriction enzymes. Many
restriction enzymes are known and each one cuts
DNA at a specific sequence of nucleotides
Restriction Enzymes
Recognition sequences
DNA sequence
Restriction enzyme
EcoRI cuts the DNA
into fragments.
Sticky end
Restriction Enzymes
Recognition sequences
DNA sequence
Restriction enzyme
EcoRI cuts the DNA
into fragments.
Sticky end
Separating DNA
• Gel electrophoresis
– Used to separate DNA fragments. DNA
fragments placed in a gel and electricity is
applied to the gel. DNA molecules are
negatively charged and move towards the
positive end of the gel. Smaller DNA
fragments move faster and farther
– This technique used to compare the genomes
of different organisms or even different people
Gel Electrophoresis
Power
source
DNA plus restriction
enzyme
Longer
fragments
Shorter
fragments
Mixture of DNA
fragments
Gel
Gel Electrophoresis
Gel Electrophoresis
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questioning?
DNA
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Scene
Using the DNA Sequence
• We can use gel electrophoresis to figure out the
DNA sequence. By knowing the DNA sequence,
we can study and compare specific genes.
Cutting and Pasting DNA
• DNA sequences can be changed by splicing
original DNA with “synthetic” pieces from
another organism
• Splicing – adding in a new section of DNA into
an existing piece of DNA
• Recombinant DNA – combining DNA from
different sources
– Ex. Taking E. coli and inserting the human gene for
making insulin into the bacteria’s DNA so that it
produces human insulin for diabetics
Making Copies of DNA
• Polymerase Chain Reaction (PCR)
technique
– Allows biologists to make many copies of
DNA
– DNA strands separated with heat, then cooled
to allow DNA Polymerase to start making new
copies of DNA
– A few dozen heat and cool cycles results in
many copies of DNA
Making Copies of DNA
DNA polymerase adds
complementary strand
DNA heated to
separate strands
DNA fragment
to be copied
PCR
cycles 1
2
3
4
5 etc.
DNA
copies 1
2
4
8
16 etc.