Download 9.1 Manipulating DNA

9.1 Manipulating DNA
KEY CONCEPT
Biotechnology relies on cutting DNA at specific
places.
9.1 Manipulating DNA
Scientists use several techniques to manipulate DNA.
• Chemicals, computers, and bacteria are used to work
with DNA.
• Scientists use these tools in genetics research and
biotechnology.
Infer: Why might so many different methods be needed to
study DNA?
9.1 Manipulating DNA
Restriction enzymes cut DNA.
• Restriction enzymes act as “molecular scissors.”
– come from various types of bacteria
- bacteria use restriction enzymes as a defense mechanism
to destroy the DNA of invading viruses.
– allow scientists to more easily study and manipulate
genes
– cut DNA at a specific nucleotide sequence called a
restriction site
Fig. 1.1 - A restriction enzyme (blue peaks)
from an E. coli bacterium helps protect
against viruses by cutting DNA (red). This
cutting "restricts" the effect of a virus on a
bacterium. (colored 3D atomic force
micrograph; magnification 63,000 X)
9.1 Manipulating DNA
• Different restriction enzymes cut DNA in different
ways.
– each enzyme has a different restriction site
9.1 Manipulating DNA
– some cut straight across and leave “blunt ends”
– some make staggered cuts and leave “sticky ends”
Infer: How would the above illustration change if TaqI left behind
blunt ends rather than sticky ends when it cuts DNA?
Summarize: How do different restriction enzymes produce different
DNA fragments from the same DNA molecule?
9.1 Manipulating DNA
Restriction maps show the lengths of DNA fragments.
• Gel electrophoresis is used to separate DNA
fragments by size.
– A DNA sample is cut with restriction enzymes.
– Electrical current pulls DNA fragments through a gel.
9.1 Manipulating DNA
– Smaller fragments move faster and travel farther
than larger fragments.
– Fragments of different
sizes appear as bands
on the gel.
Connect: Would a
mutation in a gene
always be detectable by
using restriction maps?
Why or why not?
9.1 Manipulating DNA
• A restriction map shows the lengths of DNA fragments
between restriction sites.
– only indicate size, not
DNA sequence
– useful in genetic
engineering
– used to study
mutations
Synthesize: How are restriction enzymes
used in making restriction maps?
Visual: If the purple fragment is farthest
from the green in the original DNA strand,
why is the yellow fragment farthest away
from the green in the gel?
View Restriction Enzyme
Animation: LINK
9.1 Manipulating DNA
PCR uses polymerases (enzymes) to copy DNA segments.
• PCR makes many copies of a specific DNA sequence in a
few hours.
• PCR amplifies DNA samples.
• PCR is similar to DNA replication.
Compare and
Contrast: How
are replication
and PCR
similar?
Different?
Explain.
target sequence of DNA
9.1 Manipulating DNA
PCR is a three-step process.
•
PCR uses four materials.
1. DNA to be copied
2. DNA polymerase
3. A, T, C, and G nucleotides
4. two primers – a short segment of DNA that acts as the starting point for a new strand.
9.1 Manipulating DNA
• The three steps of PCR occur in a cycle.
1. heat is used to separate double-stranded DNA molecules
2. primers bind to each DNA strand on opposite ends of the segment to be copied
3. DNA polymerase binds nucleotides together to form new strands of DNA
Graphic Analysis: Why is heat-stable polymerase needed?
Why are 2 primers needed for each DNA molecule?
How do free nucleotides attach to the existing strand?
9.1 Manipulating DNA
• Each PCR cycle doubles the number of DNA molecules.
Critical Viewing: How
many copies of DNA will
exist after one more PCR
cycle? After 3 more cycles?
PCR in Action - LINK
PCR Animation - LINK