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Sarah Berger
Mr. Miller
9, Biology P2
8 December 2010
DNA: Our Code to Life
A baby is born. A girl grows up. Neither one
of them is an exact copy of one parent. They have
traits that both their mothers and fathers have –
brown eyes, blonde hair, and good eye sight. Why is
this? One seemingly simple thing is the answer to
that question: DNA. DNA, or deoxyribonucleic acid
is a very complex molecule that resides in every cell of the body. In pictures of cells, you see
a few “X’s” in the nucleus. If those were to unravel, they would make up several six-footlong strands of DNA.
Some articles state that Watson and Crick were the first to discover our
deoxyribonucleic acid. Those facts have been proved incorrect. The first true discovery of
DNA was by a man named Friedrich Miescher. He was born in Basel, Germany in 1844.
Miescher later moved to Tübingen, Germany, where he made his great discovery. Miescher
had always been intrigued with nuclei. As he was studying them, he found something very
peculiar.
At the time, Miescher did not have very much easy access to cells. Luckily, a hospital
agreed to give him bloody bandages from the patients. In the beginning of his experiments, it
was very hard to separate the blood from the bandage without damaging the cells. After hard
work, Miescher created a sodium sulfate substance that would filter the blood cells into a
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beaker. He was then able to separate the nuclei from the cytoplasm. Once that happened,
Miescher applied an alkaline extraction then acidified the nuclei which allowed him to see
clearly the DNA. He did not know exactly what its function was, but his discovery has
inspired many scientists and the name of two universities.
Earlier referenced, Watson and Crick, Made a very large discovery to DNA. They had
studied it for a long time, but never really made any discoveries. After attending Rosalind
Franklin’s lecture in Cambridge, Watson had some ideas about the shape of a DNA
molecule. He built a model with Crick, but it was no good. They thought long and hard about
this structure, and later proposed that it was a helix with two nucleotide strands. That led to
the realization of the technical shape of the double helix (DNA).
Another person who got us one step closer to discovering the purpose of DNA was
Gregor Mendel. He almost solely discovered how heredity works. Heredity, for example is
when genes are passed from generation to
generation. In the early nineteenth century, it
was thought that traits were “blended.”
Blending was combining the traits of the
parents. For example, if one parent had long
legs and the other had short, you would have
medium length legs. Mendel knew that was not
possible. That is why he thought of heredity.
Because it would take too long to experiment
this component of DNA on humans, Mendel used pea plants. It also turned out he used those
plants because they had easily measurable traits (shape, size, and color). He started his
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experiment in the spring of 1856; Mendel knew he would need a myriad of peas, so he grew
more than 24,000 plants.
In Mendel’s first experiment, he cross-pollinated round, yellow peas with wrinkly,
green ones (Rubin). He found that their offspring were all yellow and smooth.
Mendel learned from this that there are two kinds of traits - dominant and
recessive. In this case, the dominant traits are the yellow color and the round
shape since they show up at the expense of the green color and the wrinkly shape.
He also learned that the inheritance of each trait is determined by "units" or
"factors" - now called genes (Rubin).
Through this, Mendel discovered alleles –alternate forms of a gene. To have a dominant trait,
you need to have at least one dominant allele. To have a recessive trait, one must have two
recessive alleles.
Without the components that make up deoxyribonucleic acid, we would not have
genes, not to mention peas. The four main components in DNA are guanine (g), cytosine (c),
thymine (t), and adenine (a). Cytosine and
guanine always combine; those base pairs
help hold the two sugar phosphate
backbones (shown in picture to the right).
Adenine and thymine also always combine
to help hold the backbones together.
As discovered in investigation one,
every molecule is made of two or more
atoms. In the case of the four acids, those
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atoms all happen to be: carbon, hydrogen, nitrogen, and oxygen. The chemical formula for
guanine is C5H5N5O; Cytosine’s is C4H5N3O, adenine’s formula is C5H5N5, and thymine’s is
C5H6N2O2. They are all pretty similar. It is difficult to comprehend the simplicity of our
structure. Four elements and acids can decide whether we have brown eyes or blue. It can
decide whether we are good at building things or playing violin.
DNA is a blueprint, a building block for life. All the a’s, t’s, g’s, and c’s are arranged
in a certain way. That is called a sequence. Everybody’s DNA sequence is different, even if
it is just one letter different (which is possible but not hardly plausible). The sequence is the
blueprint. It tells the body exactly what has to happen. Different parts of the sequence contain
different genes.
Every human has something in common. We all have around twenty-thousand genes.
There are two kinds of genes, recessive and dominant. Recessive genes are the least likely to
occur in a cell. Dominant are the most common genes and every living thing has at least one.
There are actually diseases that occur when a being has too many recessive genes. For
example some recessive genes are blonde hair and green eyes, albinism, and attached
earlobes.
When DNA is coiled up and scrunched
down, it takes chromosome form. Those are found
in the nuclei of eukaryotic cells. DNA does not
only determine the shape of one’s ears. It decides
what gender that organism is. Every animal
[including humans] has at least one “X”
chromosome. The way gender is determined is
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whether an animal has a “Y” chromosome or not. If it has two X’s, it’s female. If it has an X
and a Y, it’s a male. In birth, the mother gives one of her X chromosomes. The father can
give either his X or Y chromosome. Recapping the earlier stated sentence, if he gives an X, it
will be a girl. If he gives a Y, it will be a boy. They say it’s a woman’s job to bear a boy, but
it is really up to the man. Even the smallest things are different, including chromosomes. A Y
chromosome is comparatively smaller than an X [as displayed in the above picture]. Y’s have
78 genes whereas X’s have 1,098.
DNA is the basis for cloning. You may have heard of the sheep, Dolly. She was the
first large mammal to ever be cloned. It took 277 tries to clone this animal, which made the
experiment ethically questionable.
First, the scientists took a cell from a Finn Dorset white sheep’s udder. They then
removed the nucleus from it. The scientists had also previously taken an unfertilized egg
from a black-faced sheep and removed its nucleus. They fused the udder cell’s nucleus into
the unfertilized egg and implanted it into a surrogate mother.
After around 150 days, Dolly the lamb was born. She was just
about an exact copy of the Finn Dorset white sheep. The only
difference was that the mitochondria in her cells were from the
egg donor’s DNA. The reason Dolly was almost an exact copy
of the original white sheep is because of DNA. She had the
same deoxyribonucleic acid because it was the in the white
sheep’s nucleus.
I can take away from this project not only what DNA is made of, but why it is so
important. If we didn’t have it, our bodies wouldn’t know how tall to grow or how much hair
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we should have on our heads. We probably wouldn’t even have bodies. We wouldn’t be alive
because in order to live, animals have to reproduce. How are we to reproduce without this
wonderful thing called DNA?
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Works Cited
"Cloning Dolly the Sheep - AnimalResearch.info." Home - AnimalResearch.info. Web. 04 Dec.
2010. <http://www.animalresearch.info/en/medical/timeline/Dolly>.
"Dominant & Recessive Genes." Blinn College. Web. 04 Dec. 2010.
<http://www.blinn.edu/socialscience/ldthomas/feldman/handouts/0203hand.htm>.
Fetzer, Scott. "DNA." World Book. 2005. Print.
"The First Discovery of DNA » American Scientist." American Scientist Online. Web. 04 Dec. 2010.
<http://www.americanscientist.org/issues/page2/the-first-discovery-of-dna>.
Fogel, Daniel. "Gregor Mendel." World Book. 2007. Print.
"Friedrich Miescher." Wikipedia, the Free Encyclopedia. Web. 04 Dec. 2010.
<http://en.wikipedia.org/wiki/Friedrich_Miescher>.
"A Science Odyssey: People and Discoveries: Watson and Crick Describe Structure of DNA." PBS:
Public Broadcasting Service. Web. 04 Dec. 2010.
<http://www.pbs.org/wgbh/aso/databank/entries/do53dn.html>.
Roger, Klare. Gregor Mendel. New York: Enslow 1978.
Trubin, Julian. "Gregor Mendel: The Pea Plant Experiment." The Orchid Grower: A Juvenile
Science Adventure Novel. Web. 04 Dec. 2010.
<http://www.juliantrubin.com/bigten/mendelexperiments.html>.
"X and Y Chromosomes." D.G. Leahy - The New Universal Consciousness. Web. 04 Dec. 2010.
<http://dgleahy.com/dgl/p34.html>.