EXTENDED LECTURE OUT
A Scientific Revolution
(p. 222; Fig. 10.1)
Transferring genes from one organism to another falls into the realm of genetic engineering.
Genetic engineering is having a major impact o
n medicine and agriculture.
(p. 223; Fig. 10.2)
The first step of genetic engineering is to cleave the DNA that the geneticist wishes to
This process involves the use of restriction enzymes that bind specific sequences of
leotides and split the DNA in that position.
Since DNA is made up of complementary bases, both strands do not split at the same
Instead, “sticky” ends result because the DNA is cleaved at an angle.
These “sticky” ends can then be joined with a
ny other complementary sequence using ligase,
a sealing enzyme.
Since only the ends are involved, the combining of DNA from different sources (i.e., human
and mouse, or human and bacteria) is possible.
The Four Stages of a Genetic Engineering Experiment
p. 224; Figs. 10.3, 10.4, 10.5, 10.6)
Transferring genes from one organism to the next involves four stages.
Stage 1: Cleaving DNA
Cleaving DNA makes use of various restriction enzymes, each cleaving at a different
Stage 2: Producing
Recombining DNA often makes use of a bacterial plasmid, a small circular piece of
DNA separate from the normal bacterial DNA.
Stage 3: Cloning
Cloning involves getting thousands of bacterial colonies to grow, which together make
up a clone
Stage 4: Screening
The screening part of genetic engineering is often the most time
investigators must first eliminate any clones that do not contain vectors.
Secondly, investigators use a probe of ribosomal RNA to detect the presen
ce of source
Working With DNA
(p. 228; Figs. 10.7, 10.8, 10.9)
Alternative to using bacterial plasmids to produce clones of source genes, geneticists use
the polymerase chain reaction (PCR) to produce many copies of the source gene
This procedure involves locating short sequences of nucleotides, called primers, on either
side of the desired gene.
Heat is applied to a solution of DNA, the primers, nucleotides, and DNA polymerase,
which disrupts the hydrogen bonds of DNA and produc
es single strands.
When cool, the primers are bound to their complementary sequences near the desired
The enzyme, DNA polymerase, then begins at a primer and replicates the single
Many copies of the desired gene can be made in this ma
Formation of cDNA
Prokaryotes do not have exons interspersed with introns the way eukaryotes do, but
instead have continuous information encoded in the DNA.
Thus, bacteria do not have the means to remove introns from eukaryotic DNA or newly
What researchers must do rather than using the primary transcript of mRNA is to isolate
the processed mRNA from the cytoplasm that eukaryotic cells have already excised of
Reverse transcriptase is then used to make DNA from the process
ed mRNA, which
produces a type of gene called copy DNA (cDNA) that is made up only of exons.
This cDNA can then be used by bacteria to produce proteins.
DNA can be analyzed for its unique restriction endonuclease patterns, yielding
rmation that can be used to identify suspects from crimes.
Advances in Medicine
Genetic Engineering and Medicine
(p. 230; Fig. 10.10, 10.11; Tables 10.1)
Making “Magic Bullets”
Medical advances have also been made since the advent of genetic engin
Bacteria now mass
produce human insulin, the hormone that is underproduced in
Other products, such as anticoagulants to dissolve blood clots and factor VIII to promote
clotting, are now safely produced by bacteria, which eliminates the
transferring diseases from a human donor.
Vaccines have been used for years to trigger immunity to a wide variety of diseases.
Vaccines can now be made more safely by inserting the gene for a pathogen's surface
into the DNA of a harmless virus.
Such piggyback vaccines are being developed for malaria and other diseases.
Human Gene Therapy
Gene therapy, inserting normal genes into people who have inherited defective genes, is
now possible with the advent of geneti
Genetic Engineering of Farm Animals
(p. 232; Figs. 10.12)
Yet another agricultural advance has been the mass production by bacteria of bovine
somatotropin, which when fed to dairy cows, greatly enhances
Similar growth hormones enhance the size of pigs and cattle.
Genetic Engineering of Crop Plants
(p. 233; Figs. 10.14, 10.15; Table 10.2)
Certain crops, like cotton, have been engineered to be resistant to insect pests,
means these crops will not require pesticides.
Bacterial genes that produce enzymes toxic to certain plant pests have been inserted into
tomatoes and other crops so that when the insect bites into a plant, it is killed by the now
Agriculture has benefited from the genetic engineering of herbicide
The active ingredient in Roundup, called glyphosate, is easily broken down in the
environment and is thus a comparatively safe herbicide.
ng crops resistant to glyphosate means less tilling is needed, thus soils are saved
from erosion and less fuel and expense are needed to raise the crop.
More Nutritious Crops
Rice can be modified to contain more minerals, such as iron, and vitamins.
en” rice has been genetically engineered to contain vitamin A, a vitamin that is
normally insufficient in diets worldwide.
How Do We Measure the Potential Risks of Genetically Modified Crops?
Consumers worry that eating genetically
modified food might be d
angerous or that GM
crops are harmful to the environment.
Other than allergic reactions to modified proteins, dangers to the consumer appear to be
Whether GM products are potentially harmful to the environment is not yet clear.
Wilmut removed mamma
ry cells from the udder of a six
old sheep and
combined them surgically with egg cells, then applied electrical shock to kick
the cell cycle.
This cloning was the first successful cloning of an adult mammal.
The Future of Cloning
the same researchers that cloned the sheep cloned one with human genes in
every body cell.
Transgenic cloning can be expected to have a major impact on medicine and agriculture.
Cloning humans is an idea that is surrounded with controversy.
Recognize that the ability to manipulate genes and move them from one organism to another has led to
great advances in medicine and agriculture.
Explain how restriction enzymes are used.
List the four steps of a genetic engineering experiment.
in what clone libraries are and how cDNA probes can be used to screen for the presence of a
Discuss the uses and accuracy of DNA fingerprinting.
Give examples of how inserting human genes into bacteria has produced many medical advances.
ribe piggyback vaccines.
List ways in which agriculture has or will be transformed by genetic engineering.
(p. 222) moving genes from one organism to another
(p. 223 ) Excising pieces of DNA is carried out
using restriction enzymes.
(p. 225) A plasmid is a tiny ring of DNA in a bacterial cell that can replicate on its own.
(p. 225) All of the clones of the original DNA collectively are called the clone library.
(p. 227) A probe i
s a complementary sequence of nucleotides that is used to locate the gene of
(p. 228) polymerase chain reaction
(p. 228) copy DNA
(p. 230) One of the factors that leads to proper blood coagulation during a wound that is
ng in one form of hemophilia.
(p. 231) Making a piggyback vaccine involves inserting a gene for the microbe’s
surface protein into a harmless virus.
LECTURE SUGGESTIONS AND ENRICHMENT TIPS
DNA fingerprinting employs
small bits of semen, hair, nails, skin, or blood taken
from a crime scene or from a victim of a crime. The DNA is isolated from these samples, and a
restriction enzyme is employed to cut repetitive portions of DNA into portions of varying length. How
the restriction fragments happen to be is unique to each person. The fragments are then sorted
according to length using gel electrophoresis
small fragments migrate further. A membrane is used to
blot the electrophoresis gel and pick up a print of the gel.
Next, radioactively labeled DNA probes are
used to mark certain sequences of nucleotides within the suspects' DNA. The membrane is then used to
ray film, and a DNA fingerprint, with a unique series of banding patterns, is the result. No
e have the same banding patterns, with the exception of identical twins. The probability that
two people chosen at random have the same banding pattern is on the order of one in a billion. DNA
fingerprinting is a very precise method of identification.
Will Genetic Engineering Impact Traditional Agriculture?
If genetic engineering can produce
plants with complete proteins so humans have a diminished need to eat meat, what impact will this
have on traditional agriculture
for instance, on beef and pork pro
ducers? Will people still want to eat
beef, pork, chicken, and fish, or will they be willing to restrict their diets to plant nutrition only? Ask
students for their opinions on this matter. It is possible that animal protein will eventually become less
ortant as plant protein is improved. Are there, however, other nutrients supplied by animal flesh
that one cannot get from plant sources in sufficient quantity?
CHANGES TO THE NEW EDITION
Refer to the Johnson instructor web site at
for a complete list of
changes to this edition.
CRITICAL THINKING QUESTIONS
Explain why processed mRNA is used for the manufacture of a gene to be inserted into a bacterium.
cleaving DNA by using restriction enzymes facilitate the attachment of the cleaving DNA
into the plasmid?
If it is possible to genetically engineer crops to fix their own nitrogen, comment on potential effects this
accomplishment will have on the world fo
(Telephone and fax numbers and/or web sites for the sources of the following materials are listed in the
Map of Life: Science, Society, and the Human Genome Project.
James Watson discusses this
orldwide interaction to gather information about the human genome. Many of the people
interviewed also discuss bioethics and legal issues. 1992. 46 minutes.
Genome: Solving the Code of Life.
How scientists find out about an organi
sm's genome is discussed,
along with the Human Genome Project. 30 minutes.
Carolina Biological Supply,
. Transplanting animal organs into humans, with the help of genetic engineering, is the
subject of this video. Controversies surr
ounding this practice are discussed. 39 minutes.
Films for the Humanities and Sciences
The Life Revolution
. This 12
part series of videos examines the nature of genetic science which may end
up transforming the way we live. Individual videos incl
Cutting and Splicing DNA; Evolution: Man
Takes a Hand; The Human Genome; DNA Techniques; Designer Plants; Depleting the Gene Bank; Sowing
the Seeds of Disaster; Growing Synthetics; Cell Wars; Recombinant Technology; Superanimals, Super
26 minutes each.
Films for the Humanities and Sciences