Chapter9 (and Section 8-4): Genetic Engineering


14 déc. 2012 (il y a 8 années et 10 mois)

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Chapter 9:

Genetic Engineering

Section 9

Manipulating DNA

Tools of DNA Manipulation

Biologists have tools to cut, separate, and
read DNA sequences, and splice together
those sequences in almost any order

Tool #1: Cutting DNA

Restriction enzymes are proteins that cut
DNA at specific sequences

Each RE recognizes a different sequence

there are more than 100

DNA can be cut into smaller, precisely sized
fragments allowing scientists to work with a
few hundred nucleotides at a time

Restriction Enzymes

When RE cut DNA they can leave

sticky ends

Sticky ends are single
stranded regions on
either side of the cut

This is an example using

This is an example using


Other Restriction Enzymes

** Note that the restriction enzyme recognition sequences are always palindromes.

Tool #2: Separating DNA

is a technique used to
separate DNA fragments cut by restriction

Fragments move through a special gel made


Step 1: Cut DNA using RE

Step 2: Place fragments at one of the gel in

Step 3: Apply electric current. (Set gel into
buffer solution that conducts current

Negative electrode at the end with the DNA


DNA has a negative charge, so the current
will pull the DNA fragments toward the
positive electrode

Smaller fragments move through the gel
faster than larger fragments

Tool #3: Reading DNA

Once REs have cut a sample of DNA,
fragments can be placed in a test tube with
DNA polymerase and nucleotides to “read”
the fragments

Complementary DNA strand produced using
chemically modified nucleotides that stop
assembly at certain spots

fragments then
separated by electrophoresis

Reading DNA

After electrophoresis, gel has a pattern of
bands that reveals the DNA sequence

Done by computers

Used in Human Genome Project (handout)

Tool #4: Splicing DNA

Sticky ends left by some REs

If two samples of DNA are cut with the same
RE, their sticky ends can be matched up and
enzymes can be used to permanently join
the fragments

Newly joined pieces of DNA are called
recombinant DNA

Recombinant DNA

Cell Transformation

Involves inserting new genes into a cell,
changing the cell’s genetic makeup

Uses recombinant DNA

Can be done in prokaryotes and eukaryotes

Transforming Bacteria

Some bacteria have their regular DNA plus a small,
circular, extra piece of DNA called a

Plasmid can be made recombinant using REs

genes are spliced in

Recombinant plasmids are mixed into bacterial

under the right conditions they will be
picked up by some bacteria

These bacteria will then reproduce more bacteria
containing the recombinant plasmid

Transforming Eukaryotes

More difficult to get a eukaryote to accept
foreign DNA because they are more complex

Yeasts (eukaryote) contain plasmids like
bacteria, therefore are commonly used for

Animal and plant cells without plasmids have
been transformed by injecting new DNA