Download embryonic stem cells

GENE TECHNOLOGY NOTES - Mr. Nolan’s General Biology
Name: _____________
Exploring the Human Genome
Genome – all the genetic material (DNA) in an organism or species.
Human Genome Project – sequenced all nitrogen bases (A, T, C, G) in all 23 pairs of a human’s
chromosomes. Discovered that the human genome has:
 3 billion nitrogen bases
 Identified 25,000 genes
 Most genes are same as in other species
 Less that 2% of DNA codes for proteins. Remainder serves (1) regulatory roles, (2) or is left
from vestigial traits possessed by ancestor species; or (3) or was inserted by viruses into the
genomes of our evolutionary ancestors.
 Between any two humans, the amount of genetic variation is about 0.1 percent (i.e. any two
humans are 99.9% genetically the same). This means that about one base pair out of every
1,000 will be different between any two individuals. So, any two (diploid) people have about
6 million base pairs that are different.
The Human Genome Project
Small part of Human Chromosome 3
from Genome Map V
GENETIC ENGINEERING:
Here’s an application: Let’s say you wanted to genetically engineer a bacteria cell by adding a
human insulin gene to its DNA. If you can do it, then that bacteria cell will produce human insulin
protein, which is needed by diabetics. Here’s how you’d insert the human insulin gene into the
bacteria’s DNA – creating “recombinant DNA” because it has foreign DNA combined with its own
DNA.
Question: How do we cut DNA at a specific site to remove or add a specific gene?
Answer: A wide variety of “restriction enzymes” can be purchased that each recognize and cut a
unique DNA sequence. For example, you can buy a restriction enzyme (ex. EcoRI shown below)
that will cut between the C & A any time it finds the sequence CAATT. The way the enzyme cuts
the DNA leaves an exposed AATT. This is called a “sticky end” and it will “stick” to any other
segment of DNA cut by the same restriction enzyme with a TTAA sticky end, as shown in steps 2
and 3 below.
http://www.biology.iupui.edu/biocourses/N100H/images/15restriction.gif
As shown on the following page, let’s say the sequence GGATCC happens to be found near the
beginning and end on the insulin gene in human cells; and it’s also found in a particular bacteria
cell’s DNA. If you add the restriction enzyme that cuts at GGATCC to test tubes with human and
bacterial chromosomes, they’ll both be cut and sometimes the human gene will stick to the cuts in
the bacteria’s circular DNA. Now the bacteria cell will have a combination of bacterial DNA and
human DNA, so we call it Recombinant DNA. Most importantly, the bacteria cells with this
recombinant DNA will begin making human insulin protein. Many crops and live stock are
genetically modified by having foreign genes inserted into their DNA. These are Genetically
Modified Organisms (GMOs). You eat strawberries that contain a gene from fish the lowers their
freezing point. Most food in regular grocery stores is from Genetically Modified Organisms (ex.
vegetables that now make their own pesticides).
http://biology.kenyon.edu/courses/biol114/Chap08/week08b_files/mit-insulin.gif
GENE THERAPY inserts a gene from one organism or
individual into a chromosome of another organism. For
example, for a person with Parkinson’s disease, scientists
are experimenting with gene therapy to insert a gene (the
GAD gene) into a particular group of brain cells in
Parkinson’s patients. The GAD gene causes these brain
cells to make a protein that reduces the shaking in the
patient. The procedure involves using restriction enzymes
to recombine the GAD gene into a virus. The selected virus
is injected into a region of the brain. It inserts its
recombinant DNA into the brain cells, which will begin
making GAD protein. The virus is referred to as a vector
because it carries the DNA to the target cell.
Gel Electrophoresis and DNA Fingerprinting can be used to compare the DNA of several
individuals. The comparison is not based on actually sequencing their DNA (determining the sequence of
nitrogen bases). That’s too expensive and time consuming. Instead, we compare how a restriction
enzyme cuts each individual’s DNA. We use a particular region within human DNA that tends to be
especially variable from person to person. Each DNA sample is mixed with the restriction enzyme which
will cut the DNA at a certain base pattern. This leaves the DNA strand cut up into many fragments of
varying lengths depending on how often the restriction sequence was found. The process below shows
how the unique DNA fragment sizes of each person’s DNA creates a unique pattern when separated by
Gel Electrophoresis. This is the basis of DNA Fingerprinting.
http://www.stanford.edu/group/hopes/diagnsis/gentest/f_s02gelelect.gif
The DNA fingerprints of specimen #6 and #7 appear to be a match, and #5 and #8 may be
relatives. This is useful for crime scene analysis, among other things.
NORMAL FERTILIZATION vs. CLONING
Reproductive Cloning – How? As shown below, transfer nucleus from donor to egg that had
nucleus removed. Now egg with donor DNA replicates and grows into adult with all donor’s DNA.
EMBRYONIC STEM CELLS
Stem cells can differentiate and replicate into specialized cell types (ex. Liver cells, spinal cord
cells, etc.).
Embryonic stem cells can be triggered to become virtually any kind of cell, meaning they are
pluripotent. These are harvested from an embryo grown in a petri dish for six days, as shown
below.
Induced pluripotent stem cells are a type of pluripotent stem cell derived from a patient’s
somatic cell like a skin cell, by chemically forcing it to express certain genes. Basically, the
skin cell is chemically reprogrammed to become a “blank” or “wild card” undifferentiated
stem cell. Then, that stem cell can be biochemically stimulated to differentiate into
whatever cell type is needed for the patient (ex. liver cells, nerve cells, etc.) and made to
divide enough times to grow a new replacement liver or spinal cord section.