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Frontiers of
Genetics
Chapter 13
• Bacteria is a very important organism used
in DNA technology
• Specifically Escherichia coli
• Bacteria can easily exchange genes
How can bacteria exchange
genes?
Through tunnel like connections
Viruses carry bacterial genes
Bacteria take up DNA from surrounding
environment
I. Biologists have learned to manipulate
DNA
A. The Beginnings of DNA
Technology
1. Biotechnology- the use of
organisms to perform practical
tasks for humans
2. Recombinant DNA
technology- combines genes
from different sources into a
single DNA molecule
II. Biologists can engineer bacteria to make
useful products
A. Engineering Bacteria: An Introduction
1. Plasmid- a small, circular DNA
molecule separate from the much
larger bacterial chromosome
a) May carry a number of
genes and can make copies of
itself.
b)Some Bacteria are used to mass produce specific
desirable genes and proteins
c) When a plasmid replicates, one
copy can pass from one bacterial
cell to another, resulting in gene
“sharing” among bacteria.
2. Biologists use plasmids to move
pieces of DNA into bacteria.
a) First, a plasmid is removed
from a bacterial cell and the desired
gene is inserted into the plasmid.
b) The plasmid is now a combination of its
original DNA and the new DNA - it is called
recombinant DNA.
c) Then, the recombinant DNA is put back into
a bacterial cell, where it can replicate many
times as the cell reproduces, making many
copies of the desired gene. This is called
gene cloning.
Figure 13-4
Plasmids can serve as carriers of genetic information. This
diagram shows the basic technique for creating a genetically
engineered bacterial cell.
B. “Cutting and Pasting” DNA
1. First, a piece of DNA containing the
desired gene must be “cut” out of a
much longer DNA molecule.
a) restriction enzyme- an enzyme that
chops up foreign DNA into small pieces
at specific spots in the DNA sequence
2. Most restriction enzymes make staggered
cuts. These staggered cuts leave singlestranded DNA hanging off the ends of the
fragments. This is called a “sticky end”
because it is available to stick to any
sequence that is complementary to it.
a) DNA ligase (another enzyme) is used
to join the sticky ends together.
Restriction
enzymes cut DNA
molecules at
specific locations.
Splicing together
fragments of DNA
from two different
sources produces
a recombinant
DNA molecule.
C. Cloning Recombinant DNA
1. Libraries of Cloned Genes
a) Genomic Library- the
complete collection of cloned
DNA fragments from an
organism
2. Identifying Specific Genes with Probes
a) One method requires knowing at least
part of the gene’s nucleotide sequence.
1) Knowing this, a biologist can use
nucleotides labeled with a
radioactive isotope to build a
complementary single strand of
DNA.
2) Nucleic acid probe- used to locate
specific genes
b) Next, the biologist treats the DNA being
searched with chemicals or heat to separate
the 2 DNA strands. The nucleic acid probe is
mixed in with these single strands.
c) The probe tags the correct DNA portion by
pairing with the complementary sequence in
the protein-V gene.
d) Once the biologist uses this
radioactive marker to identify the
bacterial cells with the desired gene,
those cells are allowed to multiply
further, producing the desired gene
in large amounts.
D. Useful Products from Genetically
Engineered Microorganisms
1. Genetically engineered bacteria
used to make medicine (ex: insulin)
2. Recombinant DNA technology is
also helping to develop effective
vaccines (ex: hepatitis B)
III. Biologists can genetically engineer plants
and animals
A. Producing Genetically Modified Plants
1. Genetically modified organism
(GMO)- any organism that has
acquired one or more genes by
artificial means
a) Transgenic- a GMO whose
source of new genetic materials
is from a different species
Figure 13-11
To genetically modify a plant, researchers insert a plasmid
containing the desired gene into a plant cell. There, the gene
is incorporated into the plant cell's DNA. The engineered
plant cell then grows into a genetically modified plant.
B. Producing Genetically Modified Animals
1. First step is to extract an egg cell from
a female.
2. Sperm from the same species is used
to fertilize the egg in a “test-tube”
environment.
3. Then the desired gene is injected into
the fertilized egg and the egg is returned
to a uterus where it can develop into an
embryo.
C. Animal Cloning
1. The first successful clone was the
sheep named Dolly.
2. The procedure for cloning is the same
as producing a GM animal, except
that instead of inserting a gene into an
egg, an entire foreign nucleus replaces
the egg’s own nucleus.
D. The GMO Controversy
1. Can GM crops pass their new
genes to closely related plants in the
nearby wild areas?
2. Another concern is the GM plants
and animals could have unknown risks
to human consumers.
IV. DNA technologies have many applications
A. Mass-Producing DNA in a Test Tube
1. Polymerase chain reaction (PCR)a technique that makes many copies
of a certain segment of DNA without
using living cells
Figure 13-15
PCR produces multiple copies of a segment of DNA.
B. Comparing DNA
1. Gel electrophoresis- a technique for
sorting molecules or fragments of
molecules by length
a) First, each DNA sample is cut up
into fragments by a group of
restriction enzymes.
b) Next, a few drops of each sample are
placed in a small pocket or well at one
end of a gel. The other end of the gel
has a positive charge. All DNA
molecules are negatively charged, so
they move through pores in the gel
toward the positive pole.
c) The shorter DNA fragments slip more
easily through the pores of the gel.
Therefore, the shorter DNA fragments
will travel faster through the gel and be
closer to the positive end of the gel than
the longer fragments.
d) Lastly, the gel is treated with a stain
that makes the DNA visible under
ultraviolet light. The fragments show up
as a series of bands in each “lane” of the
gel.
Figure 13-16
The gel electrophoresis technique shown above can
be used to compare DNA of individuals or species.
2. Genetic markers- particular stretches
of DNA that are variable among
individuals (easy way to tell if an
individual is a carrier of a disease)
3. DNA fingerprints- an individual’s
unique banding pattern
V. Control mechanisms switch genes on and
off
A. Regulation of Genes in Prokaryotes
1. Operon- cluster of genes and
their controlled sequences
2. Promoter- control sequence on an
operon where RNA polymerase
attaches to the DNA
Figure 13-18
E. coli bacteria, natural inhabitants of your intestine, break
down the sugar lactose. The genes that code for lactoseprocessing enzymes are located next to control sequences.
Altogether, this stretch of DNA is called the lac operon.
3. Operator- a control sequence that acts like
a switch, determining whether or not RNA
polymerase can attach to the promoter
4. Repressor- a protein that functions by
binding to the operator and blocking the
attachment of RNA polymerase to the
promoter; turns off transcription
Figure 13-19
The lac operon is inactive in the absence of lactose (top) because a
repressor blocks attachment of RNA polymerase to the promoter. With
lactose present (bottom), the repressor is inactivated, and transcription of
lactose-processing genes proceeds.
B. Regulation of Genes in Eukaryotes
1. Transcription factors- proteins that
regulate transcription by binding to those
promoters or to RNA polymerases; are
activated and deactivated by chemical
signals in the cell
2. Gene expression- the transcription and
translation of genes into proteins
C. From Egg to Organism
1. Cellular differentiation- when
cells become increasingly
specialized in structure and function
Figure 13-21
Though all the genes of the genome are present in every type of
cell, only a small, specific fraction of these genes are actually
expressed in each type of cell. The yellow color indicates a gene
that is "turned on" (expressed).
D. Stem Cells
1. Cells that remain undifferentiated;
they have the potential to
differentiate into various types of
cells; may be able to help people
with disabling diseases
Figure 13-22
Present at a very early stage of human development, stem
cells have the potential to develop into any type of human
cell.
E. Homeotic Genes
1. Master control genes that direct
development of body parts in
specific locations in many
organisms
Figure 13-24
The highlighted
portions of the
fruit fly and
mouse
chromosomes
carry very
similar homeotic
genes. The color
coding identifies
the parts of the
embryo and
adult animals
that are affected
by these genes.