Preliminary Syllabus -- Biol 501, Principles of Biological
Science -- Summer, 2007
Teacher Notes for "Genetic Engineering Challenge How can
scientists develop a type of rice that could prevent vitamin A
deficiency?"[footnoteRef:1] [1: By Dr. Ingrid Waldron, Department
of Biology, University of Pennsylvania, 2014. These Teacher Notes
and the related Student Handout are available at
http://serendip.brynmawr.edu/exchange/bioactivities/geneticengineer.]
This analysis and discussion activity begins with an
introduction to vitamin A deficiency, rice seeds, and genetic
engineering. Next, several questions challenge students to design a
basic plan that could produce a genetically engineered rice plant
that makes rice grains that contain pro-vitamin A. Subsequent
information and questions guide students in developing an
understanding of the basic techniques of genetic engineering.
Students use fundamental molecular biology concepts as they think
about how to solve a practical problem. This activity can be used
to introduce students to genetic engineering or to reinforce basic
understanding of genetic engineering.
Before students begin this activity, they should have a basic
understanding of DNA, proteins, and transcription and translation.
To provide this background, you may want to use "From Gene to
Protein Transcription and Translation"
(http://serendip.brynmawr.edu/sci_edu/waldron/#trans).
These Teacher Notes propose an extension activity to introduce
students to some additional complexities of the molecular
procedures used in genetic engineering and a follow-up activity to
engage students in evaluating the arguments and evidence in favor
of and opposed to the development of genetically engineered Golden
Rice.
Learning Goals Promote student understanding of molecular
biology concepts, e.g.: Genes code for proteins (including
enzymes). The genetic code is universal. Transcription of genes is
the first step in producing proteins. (Almost) all the cells in an
organism have the same genes in their DNA, but different types of
cells have different amounts of the various proteins, which results
in the different characteristics of the different types of cells.
Differences in the rate of transcription of specific genes are a
major cause of the differing amounts of specific proteins in
different types of cells. Promoters at the beginning of each gene
play a crucial role in regulating the rate of transcription of each
gene in different types of cells. Introduce genetic engineering
concepts, including plasmids and recombinant DNA Develop an
understanding of the basic steps of genetic engineering to produce
genetically modified food plants
In accord with the Next Generation Science
Standards[footnoteRef:2]: [2: Next Generation Science Standards,
available at
http://www.nextgenscience.org/next-generation-science-standards
]
Students prepare for the Performance Expectation HS-LS3-1. "Ask
questions to clarify relationships about the role of DNA and
chromosomes encoding the instructions for characteristic traits
passed from parents to offspring." Students learn the following
Disciplinary Core Ideas: "Genes are regions in the DNA that contain
the instructions that code for the formation of proteins." (LS1.A
Structure and Function) "The instructions for forming species'
characteristics are carried in DNA. Not all DNA codes for a
protein; some segments of DNA are involved in regulatory or
structural functions " (LS3.A Inheritance of Traits) Students
engage in recommended Scientific Practices, including "constructing
explanations (for science) and designing solutions (for
engineering)". This activity provides the opportunity to discuss
two Crosscutting Concepts: "Cause and effect: Mechanism and
explanation" and "Structure and function".
This activity will also help students meet Common Core English
Language Arts Standards for Science and Technical Subjects,
including "determine the central ideas or conclusions of the text;
summarize complex concepts, processes or information presented in a
text by paraphrasing them in simpler but still accurate
terms".[footnoteRef:3] [3: From Common Core Standards Initiative,
http://www.corestandards.org/ELA-Literacy/RST/11-12 ]
Suggestions for Discussion and Background InformationTo maximize
student participation and learning, I suggest that you have your
students work individually or in pairs to complete groups of
related questions and then have a class discussion after each group
of related questions. In each discussion, you can probe student
thinking and help them develop a sound understanding of the
concepts and information covered before moving on to the next group
of related questions. I recommend that you have a class discussion
after question 4, at the end of the section on "Inserting the
Desired Genes in the DNA of Rice Plants", and at the end of the
section on "Ensuring that the Genes for the Enzymes to Make
Pro-Vitamin A are Active in Rice Grain Cells".
A key for this activity is available upon request to Ingrid
Waldron, [email protected]. Some additional background
information and suggestions for discussion are provided below.
Pro-vitamin A, also called beta-carotene, is found in many plant
foods (e.g. deep orange and dark green vegetables such as carrots,
sweet potatoes and spinach). As shown in the following diagram,
beta-carotene can be enzymatically split to form retinal (a form of
vitamin A that can be converted to the other forms of vitamin A
used in the body). Vitamin A is found in some animal foods
(especially liver). Excess vitamin A in the diet can be toxic.
Pro-vitamin A may be a safer dietary source of vitamin A since
increased intake of beta-carotene results in decreased conversion
of beta-carotene to vitamin A.
Vitamin A deficiency is widespread in children in poor
countries, resulting in an estimated 250,000-500,000 cases of
blindness and up to 2.5 million deaths each year.
White rice has been milled and polished to remove the hull, bran
and germ, leaving only the endosperm which contains thousands of
cells, abundant starch and some protein. In the figure in the
Student Handout, the endosperm is labeled as "white rice". The
major advantage of white rice is the removal of most of the oils,
which tend to become rancid when stored, especially at warm
temperatures. Brown rice has the hull removed, but keeps the germ
and bran. The major advantage of brown rice is higher levels of B
vitamins and vitamin E. Neither white rice nor brown rice provides
pro-vitamin A or vitamin A.
Question 2 will serve to remind the students that genes code for
proteins, including enzymes that synthesize other needed molecules
such as pro-vitamin A.
With respect to question 3, genetic engineering to produce
recombinant DNA in transgenic organisms is only useful because the
genetic code is universal, so any type of organism can transcribe
and translate a gene from any other type of organism.
Question 4 is designed to get students thinking about the
problems that scientists confront when developing a genetically
engineered plant. Question 4a may be challenging for students if
they do not have any background information about genetic
engineering; it is hoped that having students discuss this question
in pairs will stimulate them to come up with some possible
strategy, even if it is only injecting DNA in the rice cells'
nuclei. With respect to question 4b, some students may recognize
that it will be easier to transform a small group of embryonic
cells that can replicate the inserted gene every time the cells
divide and thus produce a rice plant that will have the inserted
gene in every one of the thousands of cells in each rice grain.
(continued)
The bacterium discussed in the section "Inserting the Desired
Genes in the DNA of Rice Plants" is Agrobacterium tumefaciens. This
bacterium can inject a crucial part of the DNA in its plasmid into
plant cells to form recombinant DNA in the plant cell nucleus. The
bacterial part of this transgenic DNA contains genes that code for
enzymes to make opines (modified amino acids that are synthesized
by the plant cells and leak out where they are consumed by the
bacteria as food) and genes that code for the production of plant
hormones that stimulate plant cell division and the production of
Crown galls (as shown below; the plasmid is called Ti or
tumor-inducing because it induces the formation of Crown galls).
These Crown galls provide abundant food for the bacteria to grow
and multiply. To make use of the genetic engineering capabilities
of this bacterium, scientists need to insert the genes for the
enzymes to make pro-vitamin A into the T-DNA of the Ti plasmid and
remove the Crown gall-inducing bacterial genes from the T-DNA of
the Ti plasmid.
6
http://www.btny.purdue.edu/Extension/Pathology/PHM/BD/picts/agrobacteriumlc.jpg
Useful sources of additional information are "Gene manipulation
in plants"
(http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-manipulation-plants/content-section-2.1)
"The Microbial World: Biology and Control of Crown Gall"
(http://archive.bio.ed.ac.uk/jdeacon/microbes/crown.htm).
This is just one example of how scientists frequently make use
of the specialized capabilities of biological systems to carry out
genetic engineering. Another example is the use of viruses to carry
DNA into human cells for gene therapy.
The section, Ensuring that the Genes for the Enzymes to Make
Pro-Vitamin A are Active in Rice Grain Cells, engages students in
thinking about the regulation of genes; this introduces an
important general concept and also provides the basis for
understanding one aspect of genetic engineering. The specific
promoter used for genetically engineering rice plants that produce
pro-vitamin A in rice grains is a promoter for an
endosperm-specific storage protein; this ensures that the
transformed genes are transcribed in rice grains.
Depending on your students, you may want to use the following
diagram to discuss the role of the promoter. Of course, the
regulation of genes in eukaryotic cells involves much more than
just a promoter, but it is the promoter that needs to be
incorporated at the beginning of the coding region of the gene as
it is prepared for use in genetic engineering.[footnoteRef:4] [4:
Additional information about preparing the genes for genetic
engineering is provided in "How to Make Transgenic Plants:
Animation Demo"
(http://cls.casa.colostate.edu/transgeniccrops/animation.html).
Explanations of the regulation of transcription are available at
http://www.nature.com/scitable/topicpage/gene-expression-14121669
and
http://sandwalk.blogspot.com/2008/09/how-rna-polymerase-binds-to-dna.html
An excellent brief video description of regulation of eukaryotic
DNA transcription is available at
http://www.hhmi.org/biointeractive/regulation-eukaryotic-dna-transcription.
"Regulating Genes"
(http://www.pbs.org/wgbh/nova/education/interactives/regulating-genes/)
is a useful introduction to Evo Devo (how changes in gene
regulation influence development and how these changes have
contributed to evolution).]
http://www.citruscollege.edu/lc/archive/biology/PublishingImages/0262l.gif
The class discussion of student responses to question 12 should
link back to issues, concepts and problems that were included in
your discussion of question 4. You may find the figure on the next
page useful for this discussion, although it shows some additional
information not included in the Student Handout and the plant it
shows is not a rice plant. If you have your students complete the
Extension Activity (see next page), your class discussion of this
extension activity should refer back to your discussion of question
12. Even if you do not have your students complete the Extension
Activity, you may want to read the second reference, which provides
helpful additional information.
(http://classes.midlandstech.edu/carterp/Courses/bio225/chap09/09-18_TiPlasmid_1.jpg
)
Extension ActivityThis extension activity is shown on the last
page of these Teacher Notes. This extension activity introduces
students to many of the complexities and specific molecular
procedures used in genetic engineering, including: the use of
restriction enzymes to make recombinant plasmids and the use of
transgenic bacteria to clone the gene of interest the need for a
marker that will allow scientists to select for plant cells that
have been transformed the need for a termination sequence for the
coding region of the gene an alternative method of transforming
plant cells (biolistic transformation using a gene gun) the need to
cross the transgenic rice plants with local breeds that have
desirable characteristics such as adaptation to local weather
conditions and resistance to a variety of plant pests and
diseases.
Some additional steps that are needed before a genetically
engineered food plant can be released for agricultural use (e.g.
testing the safety of the food and testing for possible adverse
environmental effects) are included in Extension Activity 2.The
second recommended source in Extension Activity 1 also illustrates
the iterative nature of scientific research; this reading describes
a few of the multiple steps involved in continuously improving the
effectiveness of the genetic engineering techniques by repeatedly
trying different approaches and using the results of these tests,
together with new ideas, to develop new approaches to be tested.
This iterative process has included: trying different techniques to
transform rice plant cells, research on the biosynthetic pathway
for producing beta-carotene which has shown that only two enzymes
need to be genetically engineered into the rice plant, research to
find specific versions of the genes for these enzymes that result
in production of higher levels of beta-carotene. Using this
extension activity will also illustrate the iterative nature of
learning; we need to begin with some basics, including a basic
conceptual framework, and then repeatedly improve our understanding
by incorporating new information and concepts with our previous
understanding.
Additional information about some of the technical aspects of
genetic engineering that are not included in this activity is
available from: "Development of Recombinant DNA"
(http://ocw.mit.edu/courses/biology/7-01sc-fundamentals-of-biology-fall-2011/recombinant-dna/development-of-recombinant-dna/)
"Basic Mechanics of Cloning: Restriction Enzymes and Cloning
Vectors"
(http://ocw.mit.edu/courses/biology/7-01sc-fundamentals-of-biology-fall-2011/recombinant-dna/basic-mechanics-of-cloning/)
Follow-up ActivityThe genetically engineered rice plants that
produce pro-vitamin A in rice grains are called Golden Rice. The
discussion activity, "Golden Rice Evaluating the Pros and Cons"
(available at
http://serendip.brynmawr.edu/exchange/bioactivities/GoldenRice),
engages students in evaluating the evidence and arguments related
to Golden Rice and other possible strategies for preventing vitamin
A deficiency. Students use this information to develop
evidence-based conclusions about Golden Rice and other proposed
strategies. Students also develop questions that could provide
important additional information for evaluating the arguments in
favor of and opposed to Golden Rice and other policy proposals. In
addition, students analyze how two reasonably accurate articles can
present totally opposing points of view on a complex policy
issue.
Resources for Teaching about Other Types of Genetic Engineering
Cloning, including "What is cloning?", "Click and Clone", "Why
clone?", "Cloning Myths", "What are the risks of cloning?", etc.
(http://learn.genetics.utah.edu/content/tech/cloning/) Gene
Therapy: Molecular Bandage?, including "What is gene therapy?",
"Gene Delivery: The Key to Gene Therapy", "Cystic Fibrosis: Case
Study", "Tools of the Trade", Challenges in Gene Therapy", etc.
(http://learn.genetics.utah.edu/content/tech/genetherapy/)
Extension Activity 1 Learning More about How Scientists Do
Genetic Engineering
Scientists have developed a genetically engineered type of rice
called Golden Rice which produces rice grains with substantial
quantities of pro-vitamin A. The actual process has been
significantly more complex than the basic steps described in the
activity you have completed. For useful additional information read
and view: "How do you make a transgenic plant?" (including an
animation demo from the University of Nebraska at Lincoln;
http://cls.casa.colostate.edu/transgeniccrops/how.html)
(http://cls.casa.colostate.edu/transgeniccrops/animation.html)
"Gene Manipulation in Plants"
(http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-manipulation-plants/content-section-4.3)
As you read these sources, note any additional steps or
modifications of the procedures needed to genetically engineer rice
plants that produce pro-vitamin A in their rice grains.
Prepare a revised and expanded description of the steps needed
to produce rice plants that make significant quantities of
pro-vitamin A in their rice grains.