Download Topic 4.4 genetic engineering

Topic 4.4 notes Genetic engineering and Biotechnology
4.41 Outline the use of polymerase chain reaction ( PCR)
to copy and amplify minute quantities of DNA.
( Details of methods are not required)
See page 382 of text for more detail. The piece of DNA
is multiplied by adding a promoter sequence and a heat
resistant DNA Polymerase. The DNA strands are
separated by heating… which does not denature the
enzyme. Of course, the 4 nucleotides ( A,T,G,C ) also
have to be added to the sample vial. The sample doubles
every cycle, which takes only 3 minutes. Millions of
copies can be made easily.
Note that samples can be contaminated if careful
procedures are not followed. The machine copies all
DNA in the sample, so any extraneous DNA in the
sample will also be copied. The PCR process is what has
expanded the use of DNA evidence in crime scenes, and
in a myriad of scientific investigations such as reading
the DNA code of Neanderthals.
4.4.2 State that, in gel electrophoresis, fragments of DNA
move in an electric field and are separated according to
their size.
The negative charged DNA moves to the positive end,
but smaller pieces move faster and further. This results
in a separation according to size. One can also remove
segments of DNA from the gel for further analysis once
they are sorted by size.
Restriction enzymes are used to cut DNA in specific
places. These enzymes were discovered years ago in
bacteria which use them to protect themselves against
invading viruses by cutting up their DNA.
We know of and use dozens of different restriction
enzymes. They are one the most important tools of
modern gene technology.
Each restriction enzyme recognizes and cuts the
DNA at a specific nucleotide sequence.
( eg: AAGCGCTT) Restriction enzymes can leave
" sticky ends", so that other sets of DNA can be
inserted at that point. Other restriction enzymes cut off
both strands at the same place, ( blunt ends)
Example: To compare a crime scene set of DNA
with a possible suspect's, you first amplify both sets of
DNA using a PCR machine. You then cut both sets of
DNA with the same restriction enzyme, and put through
gel electrophoresis. If the DNA is the same, it will be cut
in the same places and into the same length segments.
The gel patterns will match.
4.4.3 State that gel electrophoresis of DNA can be used in
DNA profiling
4.4.4 Describe the application of DNA profiling to
determine paternity and also in forensic investigations
[There is a variety of social implications stemming
from DNA profiling, such as identity issues for a child
who learns unexpectedly who his or her biological
father is, self-esteem problems in relationships where
the male partner learns that he did not father a child,
but also relief for crime victims when those responsible
for the crime are identified and convicted, sometimes
decades later.]
[TOK: Comparison between using blood groups
and DNA profiling for paternity: Blood group analysis
can only prove one is not the father, not that one is the
father. Even if the child has a similar blood type it does
not mean that the potential father with the same blood
type is the father.]
4.4.5 Analyse DNA profiles to draw conclusions about
paternity or forensic investigations
( see Campbell page 396)
[The outcomes of this analysis could include
knowledge of the number of human genes, the location
of specific genes, discovery of proteins and their
functions, and evolutionary relationships.
We can either emphasize the large shared content
of the human genome, which is common to all of us and
should give us a sense of unity, or we can emphasize the
small but significant allelic differences that create
biodiversity within our species, which should be
treasured. Differences in the success of human races in
coping with the modern world and the threat to some
small human tribes could be mentioned. It is important
to stress parity of esteem of all humans, whatever their
genome.]
4.4.6 Outline three outcomes of the sequencing of the
complete human genome
The outcomes include the knowledge of how many
genes code for humans. We thought there could be as
many as 100,000 genes, turns out to be around 25,000
genes.
The complete genome allows for evolutionary
comparisons of humans to other organisms. The project
included mapping the genomes of other species such as
E. coli, yeast, a nematode worm, Drosophila fly, and
the mouse.
The genome map allows scientists to locate specific
genes on specific chromosomes. This opens up the
potential of gene manipulation.
Experiments can be done on genes that are in flies
and mice that we know have direct application to
humans.
Gene expression control is critical. We can now
detect and measure which genes are turned on at which
time.
4.4.7 State that, when genes are transferred between
species, the amino acid sequence of polypeptides
translated from them is unchanged because the genetic
code is universal.
[ There is an ethical or moral question here:
whether it is right to change the genetic integrity of a
species by transferring to it from another species. The
discussion should include the wider question of selective
breeding of animals, and whether this is distinctively
different and always acceptable. The possibility of
animals suffering as a result of genetic modification
could be considered]
The genetic integrity of many species has already
been compromised. Look at Monsanto's Round-up®
resistant corn, and the Bt toxin added to crop plants.
Corn is pollinated by wind, the engineered pollen has
escaped the original engineered corn fields.
4.4.8 Outline a basic technique used for gene transfer
involving plasmids, a host cell ( bacterium, yeast or other
cell), restriction enzymes and DNA ligase.
[ The use of E. coli in gene technology is well
documented. Most of its DNA is in one circular
chromosome, but it also has plasmids ( smaller circles of
DNA). These plasmids can be removed and cleaved by
restriction enzymes at target sequences. DNA fragments
from another organism can also be cleaved by the same
restriction enzyme, and these pieces can be added to the
open plasmid and spliced together by ligase. The
recombinant plasmids formed can be inserted into new
host cells and cloned.]
The important part is using the same restriction
enzymes on both the plasmid and the target DNA
fragment. The resultant sticky ends of the DNA can
complementary bond and the ligase connects the
phosphate/sugar backbone.
4.4.9 State two examples of the current uses of genetically
modified crops or animals.
[ Examples include salt tolerance in tomato plants,
synthesis of beta carotene ( vitamin A precurser) in
golden rice, herbacide resistance in crop plants, and
factor IX ( human blood clotting) in sheep milk.]
Amgen earns billions of dollars profit each year by
inserting the gene to make the hormone that stimulates
red blood cell production into E. coli. (Erythropoetin)
Cancer patients recovering from chemotherapy need to
re-stimulate blood cell production. This is also a drug
abused by certain world class athletes… more red blood
cells, more oxygen to muscles.
4.4.10 Discuss the potential benefits and possible harmful
effects of one example of gene modification.
[There are ethical questions here about how far it
is acceptable for humans to change other species, as well
as other ecosystems, in order to benefit humans.
This is an opportunity to discuss how we can assess
whether risks are great enough to justify banning
techniques and how the scientific community can
inform communities generally about potential risks.
Informed decisions need to be made but irrational fears
should not be propagated. Consideration could be given
to the paradox that careful research is needed to assess
the risks, but performing this research in itself could be
risky. Do protester who destroy trials of GM crops
make the world safer?]
I think the best example of a genetically modified
crop that has obvious benefits and drawbacks is the
Round-up® resistant crop. Yes you get a greater yield
per acre of land, but the entire point of it is to sell and
use more of the herbacide Round-up®.
4.4.11 Define clone
A group of genetically identical organism or a
group of cells derived from a single parent cell.
4.4.12 Outline a technique for cloning using
differentiated animal cells.
(See page 408 of Campbell )Dolly, the sheep, was
created by removing the nucleus of a sheep egg, then
fusing the egg with a mammary cell of the donor sheep.
The mammary cell had been given low levels of
nutrients in a Petri dish, which de-differentiated it. An
electrical charge fused the cells and stimulated the
zygote to start dividing. The resultant zygote was
implanted in a surrogate mother who gave birth to the
clone of the donor sheep.
4.4.13 Discuss the ethical issues of theraputic cloning in
humans.
( see page 409 of Campbell)The point of stem cells
is that they are undifferentiated. They can turn into any
tissue in the body. This holds great promise for a host of
human diseases. Embryonic stem cells are the most
pluripotent, but we have discovered ways to cause cells
to revert to stem cell status. We seem to have solved the
ethical problem of using embryos to supply stem cells.