ey,
that’s against the rules!!!”
When you play a game of volleyball, you have to play by the rules. You have
to use a certain type of net of a given size and it must be a certain height
above the ground. The court has to be a certain size, and it needs to be
marked so you know where the boundaries are. You can’t carry the ball, you
can’t reach over the net, and you can’t hit the ball out-of-bounds. Each
team is allowed to hit the ball a maximum of three times before they must
send it over the net, you’re not allowed to let the ball touch the
ground, and you have to serve from behind the line.
DNA Structure and Function
Our cells and our bodies also need to play by the rules, and
unlike a game of
volleyball, they don’t have the option of “cheating.” Our DNA (which stands
for deoxyribonucleic acid) is the “rulebook,” the genetic
code material that guides and controls everything else that our cells, and
therefore our bodies, do.
DNA is a polymer, a string of similar subunits
called monomers.
In the case of DNA, the monomers are a type of chemical called nucleic
acids, and there are four kinds of those used in building DNA. Those
four are called adenine, thymine, guanine, and cytosine, but geneticists
often refer to them as A, T, G, and C. Think of them as a kind of 4-letter
alphabet, and then think of all the words of various lengths, sentences, and
paragraphs you could make from just those four “letters.” That’s what our
DNA does.
The string of nucleic acids that make up a strand of DNA are
divided into
groups of 3, and each of those groups is called a codon. Each codon
codes for one, very specific, amino acid. Each codon can only code for
exactly one amino acid (so there is no ambiguity) – for example, the codon
TTC only codes for the amino acid lysine. However, many of the 20 amino acids
are coded for by several codons (so there is redundancy) – for example, AAT,
GAA, and GAT all code for leucine.
For example, suppose that, somewhere on one of an organism’s
chromosomes, the
DNA sequence T-A-C-C-T-G-A-A-A-A-C-T happened to occur, and suppose we
wanted to figure out what kind of a protein that code would make. The first
thing we
would need to do is group those nucleic acids into groups of 3 to see what
the codons are, so that would become
TAC-CTG-AAA-ACT.
It turns out, the DNA does not directly code right to
amino acids, but
there is an intervening chemical called RNA (which is chemically similar to
DNA). One of the “rules” is that, in DNA, A and T always pair with each other,
and C and G always pair with each other. However, the RNA doesn’t have
thymine, but rather, another, slightly different nucleic acid called uracil
(symbolized by U), so wherever there’s an A on the DNA, that will pair with
a U on the RNA.
- Thus, if the DNA code is
- TAC-CTG-AAA-ACT
- That will correspond to an RNA code of
- AUG-GAC-UUU-UGA
By now, geneticists have figured out what codons code for
what amino acids.
On the Biol. 104 DNA page (link below) is a copy of a chart (edited from a
similar one in their textbook)
that allows us to “look up” that RNA code to find the corresponding amino
acids.
- Thus, if the RNA code is
- AUG——GAC——UUU——UGA
- That will correspond to the amino acid sequence
- start-aspartic acid-phenylalanine-stop
Of course, once biologists “cracked the code,” then they
wanted to manipulate and
change it, and now, it’s up to you as consumers and voters to decide, morally,
ethically, is genetic engineering a “good” or a “bad” thing? Thus, it’s
really important, even though you are not biology majors, that you read and
learn as much about this as you can!
- The gene that codes for correct insulin production has been
identified, and a copy of that gene was artificially added to the
chromosome of certain bacteria. Now, those bacteria produce/secrete insulin
that can be used to help diabetics control their blood sugar levels. In the
past, the only insulin that was available was obtained from cattle killed
in slaughterhouses, so this means lots of insulin is cheaply available. Is
that “good” or “bad”?
- The location of and code for the “bad” gene that causes cystic fibrosis
and its “correct” allele have been determined. Research is underway to obtain
a suitable type of virus, leave in the genetic code that causes it to invade/infect
our cells but remove the genetic code that allows it to make us sick, and
instead, to implant the properly-functioning allele for the cystic fibrosis
gene. The plan is that perhaps it will work to allow children with cystic
fibrosis to inhale some of these genetically-engineered viruses so that the
viruses can invade their lung tissue, implanting the “good” allele into the
cells that aren’t working right and are producing too much mucus. Is that
“good” or “bad”? Consider
- This might allow these kids to be able to breath, to lead a
more normal life, and to live longer.
- It is becoming increasingly apparent that a number of kinds of
cancer are caused by viruses, and we’re only “scratching the surface”
on beginning to figure out what viruses might be able to do that.
What if it is discovered, later on, that the virus that was used
was one that causes cancer or some other unexpected problem?
- Viruses can and do mutate (change). What if this “invented”
virus mutated in an unexpected way?
- The treatment doesn’t last “forever.” The virus only invades and
inserts the gene into the first layer of cells lining the lungs and
trachea. As those cells die, are sloughed off, and are replaced by
others, the treatment will have to be repeated.
- George Köhler and Cesar Milstein were awarded a Nobel Prize for developing
the technique involved in producing monoclonal antibodies. Human cancer
cells (lymphoma) were injected into mice so the mice’s immune systems began to
produce antibodies to fight off those foreign invaders. Mouse B-cells
(a type of white blood cell that’s part of the immune system) were isolated from
samples of the mice’s blood, and then fused with either a mouse or a human cancer
cell of a different type so the fused cells would both produce antibodies and grow
“forever” in tissue culture. The mouse antibodies were, then, further
altered to make them more like human antibodies. These “chimeric” (refering to
the mouse-human mixture) antibodies are then given to people with lymphoma, where
they bind onto the lymphoma cells, thereby marking them for destruction by the
rest of the person’s immune system. The most commonly-used monoclonal antibody
is called “rituximab” or “Rituxan®.”
- Someone decided that it would be nice to have tomato plants that are more
cold-resistant than normal. They found a species of fish that lives in very
cold areas of the ocean, identified a segment of DNA that they think
codes for something that helps the fish to be more cold-tolerant, isolated
that piece of DNA, and managed to inject/transplant it into the cells of
tomato plants. Is that “good” or “bad”? Consider
- DNA splicing is not an exact thing. They probably get the gene
they want to get, but they’re also getting “unknown” genetic code
on either end. What will that “spare” genetic code do?
- Because they (correctly) perceive that the general public probably
would be hesitant to buy their genetically engineered tomatoes, they
are fighting to convince the government that they should not have to
label them as such. What if someone is a vegan and does not want to
eat fish? What if someone, for whatever personal reason, just doesn’t
want to eat genetically-engineered foods – should that person not be
allowed to make that choice?
- What if someone is highly allergic to fish, more specifically, to
the protein coded for by that gene? What if that person goes into
a restaurant, orders a salad, unsuspectingly eats a tomato, and goes
into anaphylactic shock?
- What if, 20 years from now, some new long-term problem becomes
apparent, and suddenly, we’re told, “Gee, I’m sorry, but...”?
- Someone came up with the idea to genetically engineer corn plants to be
resistant to a certain herbicide (made by the same company, of course) with
the idea that if farmers plant their corn and spray their herbicide all over
the place, the corn will not be killed and the “weeds” will. Oh, by the way,
while they were at it, they further genetically-engineered the corn so the
seeds from those plants would not sprout and grow, so farmers would have to
purchase new corn seed from them every year. Is that “good” or “bad”?
Consider
- Corn can and does occasionally interbreed with grass-type “weeds”
that are close relatives. In doing so, the herbicide-resistance gene
can “jump to” and become incorporated into the local population of
“weeds.” We are already seeing a number of “weed” species that are
now resistant to that herbicide.
- Big, agribusiness, corporate farms can afford to spend money to buy
new seed every year. Most family farmers cannot, and they rely on
saving seed from one year to plant the next year. Because of that,
most of them do not plant this genetically-engineered corn. However,
corn is wind-pollinated, and when pollen from the genetically-engineered
corn on the big agribusiness farm blows into a family farmer’s corn
field and fertilizes that corn, those seeds will be sterile, too,
possibly ruining that small farmer’s already-fragile economic
state.
- And... the small farmers who have been lucky enough to get some
seed to sprout and grow, anyway, have been sued by the giant corporation
for planting “their” seeds without purchasing them, first.
- Small farms that are trying to adhere to strict organic farming
principles have had what would have been a fine crop of organic corn
that would have sold for a premium price
“contaminated” by pollen from nearby, genetically-engineered corn,
and thus, rendered practically worthless.
- According to governmental wisdom, it is legal to use
genetically-engineered corn to feed cattle, then slaughter and eat
the cattle, but it is not legal to use genetically-engineered
corn to make, for example, taco shells, and feed it directly to
humans.
- When farmers take their corn to the grain elevator to sell it,
there are not separate silos for genetically-engineered and normal
corn. It all gets dumped in, together. It would be too complicated
and costly for the grain companies to try to keep track of it separately.
- It’s illegal to import or plant this stuff in most European
countries.
- On a related note, they’ve also genetically engineered corn to contain a
gene from a type of bacterium (called BT) that infects and kills caterpillars.
The reason for this is that there is a species of moth caterpillar that
bores into corn stems, and with agribusiness planting mile after mile of
caterpillar host plants, that makes for a really large dinner table. This
has been very controversial, because other people feel there is some pretty
strong evidence that when the pollen from this corn settles on leaves of other
plants that are food for “good” caterpillars like monarch and swallowtail
butteflies, and they eat it along with the leaves, they will get sick and
die.
Oh, in case you’re interested, in many of the cases
mentioned above, “they”
is Monsanto (the company that also brings you Saccharin, Aspartame, Roundup,
PCBs, Agent Orange, and Bovine Growth Hormone [rBGH] in your milk, as well as
genetically-engineered corn, cotton, canola, soy, tomatoes, and strawberries,
just to mention a few).
If you have the time, go to their Web site
and read how they pat themselves on the back for all the “good” things
they’re doing. However, if you’d like the real story, do a Google search
and see what everyone else is saying.
Background Information
Links to Related Information on Our Web Server
The following Web pages contain information related to
DNA and genetic engineering.
- Bio Lecture DNA
- Information on DNA structure and replication, and genetic engineering
- Dr. Fankhauser’s Genetic Engineering Web Page
- Information on the possible dangers associated with genetic engineering
Your Assignment
Genetics “Practice”
There will be only one, combined assignment for this week’s
topics (mitosis and meiosis, genetics, and DNA). Thus even though this will
appear on each of those three pages to remind you, you only need to do it once.
Genetics is one of those things that just needs lots of practice to “get it.”
The grading criteria for this assignment are given below, and you should also
refer to those as you work on the assignment.
A total of 32 points is possible.
- Mitosis
- Read through the Biol. Lecture Web pages on mitosis and meiosis to
become familiar with those processes, how they are the same, and
how they differ.
- Find/collect a group of “similar” but distinguishable objects such as
coins, pieces of string or yarn, socks, or whatever is handy. These will
be used to represent the chromosomes in the nucleus of a cell. Also,
obtain several, longer pieces of string or yarn to represent cell and
nuclear membranes.
- Make a cell. Use a longish piece of string to make a circle to
represent the cell membrane. Use a shorter piece to make a smaller
circle inside to represent the nuclear envelope. This organism will
have 6 chromosomes (3 from the father and 3 from the mother). For
this you will need 3 pairs of something; for example a pair each of
black, red, and blue socks or a pair each of pennies, nickles, and dimes
(or whatever is handy that will suit the purpose). Put these 6
“chromosomes” into the nucleus of the cell.
- Just before mitosis happens, the chromosomes replicate, but the
halves (called sister chromatids) stay attached. Simulate this
by stacking 6 more identical
objects (well, come as close as you can...) on top of the existing
6 “chromosomes”. For example, stack another penny on top of each of
the two existing pennies, another nickle on top of each of the two
existing nickles, etc.
- In prophase of mitosis, one thing that happens is that the nuclear
envelope disintegrates. To demonstrate this, remove the string that’s
the nuclear envelope and set it aside.
- In metaphase, all the chromosomes line up along the “equator” of
the cell. Line up your 6 “chromosomes” (each with its partner still
on top) in a row (single-file) across the middle (“equator”) of your
cell.
- In anaphase, the halves of the chromosomes separate and travel to
opposite poles of the cell. For each of your 6 “chromosomes,” now is
the time to separate the partners. For each of the 6 stacks of 2, move
one of the two items to the “north pole” of the cell and one to the
“south pole” of the cell. When you’re done, each pole should have a
collection of 6 objects/“chromosomes” identical to the 6 with which you
began.
- In telophase, the nuclear envelopes re-form and the cell divides
into two. First, find a piece of string with which to form a circle
around each of the two groups of “chromosomes” to show the nuclear
envelope re-forming. Then, near the “equator” of the cell, pinch/poke/move
the string that represents the cell membrane in toward the center until
the cell is divided into two. Optionally, you could replace that one
string with two separate ones to remind yourself that you now have two
separate cells.
- Congratulations! You have done mitosis.
- Meiosis
- OK, now try meiosis...
Make another cell just like the previous one. Give it a cell membrane
and nuclear envelope, again, as well as the same 6 chromosomes.
- As above, just before meiosis happens, the chromosomes replicate,
as they do in mitosis, so add the matching halves back on top, again.
- In prophase I of mitosis, one thing that happens is that the nuclear
envelope disintegrates. To demonstrate this, remove the string that’s
the nuclear envelope and set it aside. Something else, very important,
happens during prophase I: the chromosomes pair up. Move your
“chromosomes” around so that the matching ones are next to each other.
For example, put the two stacks of pennies (or the two stacks of black
socks) next to each other, the two stacks of nickles next to each other,
etc.
- In metaphase I, the chromosomes line up along the “equator” of
the cell, again, but this time still in their pairs.
Line up your 3 pairs of “chromosomes” (each with its partner still
on top) in a row (double-file, side-by-side) across the middle (“equator”)
of your cell.
- In anaphase I, the pairs of chromosomes separate and travel to
opposite poles of the cell. For each of your 3 pairs of “chromosomes,”
now is the time to separate the pairs. Keeping the partner halves still
stacked together, move one whole stack from each of the 3 pairs to the
“north pole” of the cell and one to the “south pole” of the cell.
When you’re done, each pole should have 3 stacks of objects/“chromosomes,”
one of each of the kinds with which you began.
- In telophase I, as before the nuclear envelopes re-form and the
cell divides into two. Similar to what you did above, re-form the
nuclear envelopes and divide the cell into two. When you have the
cell membrane all the way “divided,” go ahead and substitute two
pieces of string for the one, to represent the fact that you now have
two, separate cells.
- This time, however, you’re not done yet. There is another cell
division yet to go. Once again, in prophase II, the nuclear envelopes
disintegrate, so remove those from both of the cells.
- In metaphase II, the chromosomes line up along the “equator” of
the cell, in single-file, similar to what happened in mitosis. In each
of your cells, once again, line the 3 “chromosomes” up, single-file, along
the equator of that cell.
- In anaphase II, you finally get to separate your stacks of “sister
chromatids.” From each of your stacks, move one partner to the “north
pole” and one to the “south pole” of that cell. Between the two cells,
you should now have a total of 4 groups of 3 items.
- In telophase II, once again, the nuclear envelopes re-form. You’ll
now need 4 pieces of string so you can make a circle around each of the
new nuclei. Also, in each cell, once again, pinch in the middle to form
2 cells out of each one, then (optionally) replace each of those cell
membranes with 2 separate cell membranes (strings) for each of the new
daughter cells. When you are done, you should end up with 4 daughter
cells, each with 3 chromosomes.
- Congratulations! You have done meiosis and you now have 4 eggs or
sperm.
- Fertilization
- Don’t get rid of your eggs/sperm just yet! To do this the “official”
way, you could go through the whole process of meiosis with a
different “parent” so that you end up with 4 sperm from one parent and 4
eggs from the other parent. However, to simplify things, from the 4 you
have sitting there, now, pick one to be an “egg” and one to be a “sperm,”
and think of them as having come from different parents.
- If necessary (if they're a distance apart), the sperm will have to
“swim” over to where the egg is, until they are touching. That might be
easier to do if you slide the nucleus and chromosomes onto a sheet of
paper so you can move it as one unit. To make the next
part easier, you might want to reposition the cell membranes of the
egg and the sperm cells
so the loose ends of the strings meet where the egg and sperm are
touching.
- Now, the whole sperm nucleus (just the nucleus, not the whole cell)
has to go inside the egg cell, leaving its cytoplasm and cell membrane
behind. If you previously placed the nucleus on a sheet of paper, just
slide the whole thing over, into the egg cell, and as close to the egg
nucleus as you can get it. When that step is complete, both nuclei
should be within the egg cell, and the egg cell membrane should be
“closed” all around (the hole where the sperm nucleus entered closes
up).
- Then, the sperm and egg nuclei unite, so put all of the chromosomes
from both into one nucleus (and set aside the spare string). How do
the number and types of chromosomes compare with what you started with
before meiosis?
- Congratulations! You have just conceived a baby!
- Think about and summarize
How are mitosis and meiosis similar, and how are they different?
Where in a person’s body does mitosis happen, and where does meiosis
happen? In what way(s) are meiosis and fertilization the “opposite”
of each other?
- Genetics
- Genes are located on chromosomes. Thus, as the chromosomes move
around in meiosis and segregate into the daughter cells, they carry
with them all of the chromosomes located on them. For example, in
the meiosis demonstration you just did, suppose the first set of
“chromosomes” (the pennies?) contained the gene for eye color. If the
individual was heterozygous for eye color, one chromosome would
carry a B allele for “brown”, and the other chromosome would
carry a b allele for “blue”. When the chromosomes replicate, they
make an exact copy of themselves, so the coins/socks/yarn you stacked
on top of each other would carry the same allele as each other. Suppose
the nickles (the second pair of “chromosomes”) carry a gene for
tongue-rolling, but if the individual is heterozygous there, too, one
nickle would have an R allele (for “rolling”) while the other one
would have an r allele (for “non-rolling”). Suppose the third pair
of “chromosomes” (the dimes?) contain a gene for ability to taste a
certain kind of test paper called PTC paper, and suppose, again, that
the individual is heterozygous for this gene, too. Then one dime
“chromosome” would carry a T allele (for “taster”) and the other
would carry a t allele (for “non-taster”).
- If it helps you to visualize what’s going
on, here, set up the meiosis demonstration, again, but
this time, go ahead and label the “chromosomes” with the appropriate
genes they contain. When you get to metaphase I and you’re lining up
the pairs of chromosomes in the center of the cell, don’t be concerned
whether all of the B, R, and T alleles are on the same “side” or not,
because in “real life” it’s pretty much a 50:50 chance for each pair
which one will line up on the “north” side and which will line up on the
“south” side. This means that when the chromosomes do their first
division in anaphase I, it’s a 50:50 chance for each pair which
one will wind up at whichever pole of the cell. Thus, for example,
if you end up with BrT at the “north pole,” that’s just one
possible example of what might happen in real life.
- Understanding how genetic crosses work is best accomplished by
working practice problems and Punnett squares. Spend time working with
the Genetics Practice Problems Web
page until you feel comfortable working these kinds of problems.
- When you submit your work for this assignment, the data-submission
Web page will automatically generate several genetics problems which
you will be asked to work out.
- DNA
Do a Web search to find out more information on one kind of
genetically-modified organism (GMO) and summarize what you found out.
Terms for which to search might include “GMO”, “genetic engineering”,
“genetically-modified”, “frankenfood”, “monoclonal antibody”, “rituxan”,
“rituximab”, “epratuzumab”, “galiximab”, “campathin”, “alemtuzumab”,
and/or “roundup-ready”, etc. Make sure you tell
what organism was modified, what gene(s) were inserted, where those
genes came from (what other organism), and the reason why somebody
thought it would be a good idea to do that. What are some of the
advantages or benefits that proponents claim will result from
this, and what are some of the disadvantages or problems that
opponents claim will come as a result of this. Based on what you’ve
found out, would you say that, ethically/morally, this is a “good”
thing or a ”bad” thing? Give scientific reasons to justify your
point-of-view.
- At this point, if you are a registered student, you should
submit your work.
Grading Criteria
1. Mitosis and Meiosis: |
2 | — | The student clearly demonstrated that (s)he knows the difference between mitosis and meiosis |
1 | — | The differences between mitosis and meiosis were included and was at least partially correct |
0 | — | Mitosis and meiosis were incorrectly distinguished from each other or the distinction between the two was not included |
|
2 | — | The student, obviously, went beyond the minimum requirements of the assignment |
1 | — | The student adequately completed the assignment |
0 | — | The student completed considerably less of the assignment than what was required |
2. Genetics Problems (for each problem × 3 problems): |
2 | — | The male gametes (sperm) were correctly specified (genotypes) and placed |
1 | — | The genotypes and/or placement of the sperm were partially incorrect |
0 | — | The genotypes and/or placement of the sperm were wrong or missing |
|
2 | — | The female gametes (eggs) were correctly specified (genotypes) and placed |
1 | — | The genotypes and/or placement of the eggs were partially incorrect |
0 | — | The genotypes and/or placement of the eggs were wrong or missing |
|
2 | — | The genotypes of the offspring were correct |
1 | — | The genotypes of the offspring were partially incorrect |
0 | — | The genotypes of the offspring were wrong or missing |
3. Genetically-Modified Organism: |
2 | — | Thorough/complete information on the chosen GMO was included |
1 | — | Adequate information on the chosen GMO was included and was at least partially correct |
0 | — | Information on the chosen GMO was too sketchy or absent or was incorrect |
|
2 | — | An ethical point-of-view was included and was backed up by thoroughly-researched facts |
1 | — | The student’s point-of-view was included, but was backed up only by personal opinions/beliefs and/or partially incorrect or skimpy facts |
0 | — | The student did not include his/her ethical point-of-view, or there was no justification given for how/why that opinion was reached |
|
2 | — | The student, obviously, went beyond the minimum requirements of the assignment |
1 | — | The student adequately completed the assignment |
0 | — | The student completed considerably less of the assignment than what was required |
4. Overall: |
2 | — | The grammar, English usage, punctuation, and spelling were very good |
1 | — | The grammar, etc. were OK |
0 | — | The grammar, etc. were poor |
|
2 | — | It is evident that the student used much insight, thoughtfulness, and critical thinking when completing this assignment |
1 | — | The student adequately thought about the assignment – there was, perhaps, a bit of “fuzzy thinking” in a couple places |
0 | — | The assignment gives the appearance of being “slapped together” just to get it done, with little evidence of thoughtfulness |
Total Possible: |
32 | — | total points |
Copyright © 2006 by J. Stein Carter. All rights reserved.
This page has been accessed times since 15 Nov 2006.