DNA The Code of Life

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DNAThe Code of Life
The Molecular Basis of Inheritance
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DNA
Deoxyribonucleic acid The information
necessary to sustain and perpetuate life is found
within a molecule. This is the genetic material
that is passed from one generation to the
next---a blue print for building living organisms.
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History
Although we now accept the idea that DNA is
responsible for our biological structure, But in
the early 1800s it was unthinkable for the
leading scientists and Philosophers that a
chemical molecule could hold enough information
to build a human. They believed that plants and
animals had been specifically designed by a
creator.
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History
Charles Darwin is famous for challenging this
view. In 1859 he published 'The Origin of
Species expressing that living things might
appear to be designed, but were actually the
result of natural selection. Darwin showed that
living creatures evolve over several
generations through a series of small changes.
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History
In the 1860s Darwin's ideas were supported when
genetics was discovered by Gregor Mendel. He
found that genes determine the characteristics a
living thing will take. The genes are passed on
to later generations, with a child taking genes
from both its parents. The great mystery was
where and how is this information stored?
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History
The main conclusions made by Mandle
were SEGREGATION Inherited traits are
controlled by genes, which are in pairs. When sex
cells are created one gene from each pair goes
into the gamete. When two gametes fuse at
fertilization, the offspring has two copies of
each geneone from each parent. INDEPENDENT
ASSORTMENT The genes for different traits are
sorted into gametes independently of other genes.
So one inherited trait is not dependent on
another. DOMINANCE Where there are two
different forms of a gene are present in a pea
plant, the one which is dominant is the one that
is observed.
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History
Search for genetic material In 1870, a German
scientist named Friedrich Miescher had isolated
the chemicals found in the nucleus. These were
proteins and nucleic acids. While he found these
nucleic acids interesting, and spent a great deal
of time studying their chemical composition, he
wasnt alone in believing that proteins were more
likely to be the chemicals involved in
inheritance, because of their immense
variability. They were made up of 20 different
building blocks (amino acids), as opposed to the
mere 4 building blocks of nucleic acids.
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History
Search for genetic material In the early 1900s,
Phoebus Levene, who also believed that proteins
must be the chemicals of inheritance, studied the
composition of nucleic acids. He discovered that
DNA is a chain of nucleotides, with each
nucleotide consisting of a deoxyribose sugar, a
phosphate group and a nitrogenous base, of which
there were four different types. He proposed that
the four different types of nucleotide were
repeated over and over in a specific order. This
would make DNA a relatively simple repeat
sequence no wonder DNA wasnt considered to be
smart enough to code for all of life!
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History
Search for genetic material 1928 Frederick
Griffith transforming principle
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History
Search for genetic material
It wasnt until 1944 that Oswald Avery and his
colleagues, who were studying the bacteria
which causes pnuemonia, Pneumococcus, discovered
by process of elimination that bacteria contain
nucleic acids, and that DNA is the chemical which
carries genes. Despite the conclusive results of
Averys experiments, the theory of nucleic acids
being the genetic material was still not a
popular one, but experiments Performed with
viruses also showed that nucleic acids were the
genetic material and this confirmed Averys work.
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History
Search for genetic material 1952 -
Hershey-Chase Experiment
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History
Search for genetic material

• Classic experiments for evidence Griffith
  transformation Hershey-Chase DNA necessary
  to produce more virus
• Other supporting evidence DNA volume doubles
  before cells divide Chargaff ratio of
  nucleotides A T and G C

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The Discovery
The DNA molecule was discovered in 1951 by
Francis Crick, James Watson and Maurice Wilkins
using X-ray Diffraction. In Spring 1953,
Francis Crick and James Watson, two scientists
working at the Cavendish Laboratory in Cambridge,
discovered the structure of the DNA a double
helix, or inter-locking pair of spirals, joined
by pairs of molecules.
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The Discovery
The seed that generated this was
Watsons presence at a conference in Naples in
1951, where an x-ray diffraction picture from
DNA was shown by Maurice Wilkins from Kings
College in London. This made a strong impression
on Watson the first indicationthat genes might
have a regular structure.
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History
Search for genetic material
James Watson joined the unit (its first
biologist) and began by trying to crystallize
myoglobin for Kendrew. The unsuccess of this
left much time for discussion with Crick, whose
office he was sharing, and the topic of DNA
structure naturally arose particularly how to
determine it. They were inclined to follow the
method of Pauling who had deduced the a-helical
structure by building a model consistent with
the x-ray patterns from fibrous proteins. Like
proteins, DNA was built from similar units the
bases adenine (A) thymine (T) guanine (G) and
cytosine (C), and so it seemed likely that DNA
too had a helical structure. The publishedx-ray
patterns of DNA were not very clear, and so
contact was made with Kings. Watson attended a
DNA colloquium there in November 1951, at which
Rosalind Franklin described her results.
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History
Search for genetic material
Watson brought back a less-than-accurate
account to Cambridge, but with Crick produced a
three-strandmodel structure only a week later.
Invited to view this,Franklin pointed out that it
was inconsistent with her results it had
thephosphate groups on the inside whereas her
results showed they were on the outside,and the
water content was too low. The work at Cambridge
stopped abruptly for a bit.
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History
Search for genetic material
In July 1952, Erwin Chargaff visited the unit and
told of his 1947 findings that the ratios of A/T
and G/C were unity for a wide variety of DNAs.
Crick became convinced that base pairing was the
key to the structure. Prompted by receiving a
flawed manuscript on DNA structure from Pauling,
Watson again visited Kings and Wilkins showed
him a DNA x-ray pattern taken by Franklin of the
pure B-form showing clear helical
characteristics, plus the intense 10th layer line
at 3.4A and a 20A equatorial reflection
indicating the molecular diameter. Perutz also
showed them a report on the work of the Kings
group which gave the space group of the
crystalline A-form as C2, from which Crick
deduced that there were two chains running in
opposite directions.
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History
Search for genetic material
Watson began pursuing the idea of hydrogen
bonding using cardboard cutouts of the four
bases. He found that (AT) and (GC) could be
bonded together to form pairs with very similar
shapes. On this basis a model was built
consistent with the symmetry and with Chargaffs
results, and a paper was published in April 1953
in Nature accompanied by ones from the Wilkins
and Franklin groups at Kings. Watson and
Cricks paper ends with the oft-quoted line It
has not escaped our notice that the specific
pairing we have postulated immediately suggests a
possible copying mechanism for the genetic
material.
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The Evidence
Search for genetic material James Watson and
Francis Crick used this photo with other evidence
to describe the structure of DNA.
X-ray diffraction photo of DNA Image produced by
Rosalind Franklin
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Watson and Crick with their
DNA model

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The Scientists

Francis Crick was born in 1916. He went to London
University and trained as a physicist. After the
war he changed the direction of his research to
molecular biology. James Watson was an American,
born in 1928, so aged only 24 when the discovery
was made. He went to Chicago University aged
only 15 and had already worked on DNA.
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The Nobel Prize

Crick, Watson and Wilkins won the Nobel Prize for
medicine in 1962. Maurice Wilkins was at King's
College, London and was an expert in X-ray
photography. His colleague, Rosalind Franklin,
did brilliant work developing the technique to
photograph a single strand of DNA. She received
little recognition for this at the time and died
tragically of cancer in 1958, so could not be
recognised in the Nobel Award.
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Watson Crick

What they deduced from Franklins X-ray data
Double helix Uniform width of 2 nm Bases
stacked 0.34 nm apart Chargoffs rules
Adenine pairs with thymine Cytosine pairs with
guanine
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Watson Crick

What they came up with on their own Bases face
inward, phosphates and sugars outward
Hydrogen bonding Hinted at semi-conservative
model for replication
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KEY PLAYERS Oswald Avery (1877-1955) Microbiolo
gist Avery led the team that showed that DNA is
the unit of Inheritance. One Nobel laureate has
called the discovery "the historical platform
of modern DNA research", and his work inspired
Watson and Crick to seek DNA's structure.

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KEY PLAYERS Erwin Chargaff (1905-2002)
Chargaff discovered the pairing rules of DNA
letters, noticing that A Matches to T and C to
G. He later Criticized molecular biology, the
discipline he helped invent, as "the practice of
biochemistry without a licence",and once
described Francis Crick as looking like "a
faded racing tout".

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KEY PLAYERS Francis Crick (1916- )Crick
trained and worked as a physicist, but switched
to biology after the Second World War. After
co-discovering the structure of DNA, he went on
to crack the genetic code that translates DNA
into protein. He now studies consciousness at
California's Salk Institute.
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KEY PLAYERS Rosalind Franklin (1920-58)
Franklin, trained as a chemist, was expert in
deducing the structure of molecules by firing
X-rays through them. Her images of DNA -
disclosed without her knowledge - put Watson and
Crick on the track towards the right structure.
She went on to do pioneering work on the
structures of viruses. .

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KEY PLAYERS Linus Pauling (1901-94) The titan
of twentieth-century chemistry. Pauling led the
way in working out the structure of big
biological molecules, and Watson and Crick saw
him as their main competitor. In early 1953,
working without the benefit of X-ray pictures,
he published a paper suggesting that DNA was a
triple helix.

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KEY PLAYERS James Watson (1928- )Watson went
to university in Chicago aged 15, and teamed up
with Crick in Cambridge in late 1951. After
solving the double helix, he went on to work on
viruses and RNA, another genetic information
carrier. He also helped launch the human genome
project, and is president of Cold Spring Harbor
Laboratory in New York.

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KEY PLAYERS Maurice Wilkins (1916- )Like
Crick, New Zealand-born Wilkins trained as a
physicist, and was involved with the Manhattan
project to build the nuclear bomb. Wilkins
worked on X-ray crystallography of DNA with
Franklin at King's College London, although
their relationship was strained. He helped to
verify Watson and Crick's model, and shared the
1962 Nobel with them.

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Structure

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Structure

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Structure

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Structure

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Structure

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Structure
There are 4 different nucleotides in DNA
Adenine pairs with Thymine Guanine pairs with
Cytosine
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Structure
Adenine pairs with Thymine Guanine pairs with
Cytosine
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Structure
Does DNA fit the requirements of a hereditary
material?
Requirement DNA component
Has biologically useful information to make protein Genetic code 3 bases code for 1 amino acid (protein)
Must reproduce faithfully and transmit to offspring Complementary bases are faithful found in germ cells
Must be stable within a living organism Backbone is strong covalent bonds hydrogen bonds
Must be capable of incorporating stable changes Bases can change through known mechanisms
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Protein Synthesis
DNA carries the instructions for the production
of proteins.A protein is composed of smaller
molecules called amino acids, and the structure
and function of the protein is determined by the
sequence of its amino acids. The sequence of
amino acids, in turn, is determined by the
sequence of nucleotide bases in the DNA. A
sequence of three nucleotide bases, called a
triplet, is the genetic code word, or codon,
that specifies a particular amino acid.
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Protein Synthesis
Protein synthesis begins with the separation of a
DNA molecule into two strands. In a process
called transcription, a section of the sense
strand acts as a template, or pattern, to produce
a new strand called messenger RNA (RNA). The RNA
leaves the cell nucleus and attaches to the
ribosomes, specialized cellular structures that
are the sites of protein synthesis. Amino acids
are carried to the ribosomes by another type of
RNA, called transfer (RNA). In a process called
translation, the amino acids are linked together
in a particular sequence, dictated by the RNA, to
form a protein.
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Replication
Before replication, the parent DNA molecule has 2
complementary strands
First the 2 strands separate
Each old strand serves as a template to
determine the order of the nucleotides in the new
strand
Nucleotides are connected to form the backbone
now have 2 identical DNA molecules.
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Replication
DNA Replication is simple, but it takes a large
team of enzymes and proteins to carry out the
process

• Helicase unwinds the molecule
• Single-strand binding protein stabilized ssDNA
• Primase initiates the replication with RNA
• DNA polymerase extends the new DNA
• Second DNA polymerase removes the RNA
• DNA ligase joins all the fragments

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1971-Smith Nathans

Discovery of restriction endonucleases Hamilton
Smith Discovered HindII in Haemophilus
influenzae Daniel Nathans Used HindII to make
first restriction map of SV40
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1972
- Paul Berg Produces first recombinant DNA using
EcoRI 1973 -Boyer, Cohen
Chang Transform E. coli with Recombinant plasmid

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1977
- Genentech, Inc. Company founded by Herbert
Boyer and Robert Swanson in 1976 Considered the
advent of the Age of Biotechnology First human
protein (somatostatin) produced from a transgenic
bacterium. Walter Gilbert and Allan Maxam
devise a method for sequencing DNA.

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1978 David Botstein discovers RFLP
analysis 1980 U.S. Supreme Court rules that
life forms can be patented Kary Mullis develops
PCR. Sells patent for 300M in 1991

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1981 First transgenic mice produced 1982 The
USFDA approves sale of genetically engineered
human insulin 1983 An automated DNA sequencer
is developed A screening test for Huntingtons
disease is developed using restriction fragment
length markers.

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1984 Alec Jeffreys introduces technique for DNA
fingerprinting to identify individuals 1985
Genetically engineered plants resistant to
insects, viruses, and bacteria are field tested
for the first time The NIH approves guidelines
for performing experiments in gene therapy on
humans

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1987 invention of YACs (yeast artificial
chromosomes) as expression vectors for large
proteins 1989 National Center for Human Genome
Research created to map and sequence all human
DNA by 2005.

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1990 UCSF and Stanford issued their 100th
recombinant DNA patent and earning 40 million
from the licenses by 1991. BRCA-1 discovered
First gene therapy attempted on a
four-year-old girl with an inherited immune
deficiency disorder.

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1992 U.S. Army begins "genetic dog tag"
program 1994 The Flavr Savr tomato gains FDA
approval The first linkage map of the human
genome appears 1995 The first full gene
sequence of a living organism is completed for
Hemophilus influenzae. O.J. Simpson found not
guilty despite DNA evidence

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1996 The yeast genome, containing approximately
6,000 genes and fourteen million nucleotides, is
sequenced. 1997 Dolly cloned from the cell of
an adult ewe DNA microarray technology developed

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1997 The genome of the bacterium E. coli, a
classic model organism for studying
microbiological and molecular genetic mechanisms,
and a natural symbiont in the human digestive
tract, is completely sequenced, revealing about
4,600 genes among about four and one-half million
nucleotides.

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1998 The genome of a nematode worm
Caenorhabditis elegans, a key model organism for
investigating genetic regulation of development,
is sequenced, revealing approximately 18,000
genes among some 100 million nucleotides of DNA
sequence.

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1999 1,274 biotechnology companies in the
United States At least 300 biotechnology drug
products and vaccines currently in human clinical
trials Human Genome Project is on time and
under budget, the complete human genome map
expected in five years or less

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1999 Jesse Gelsinger, an eighteen year-old with
a genetic disorder affecting liver metabolism,
dies from an immune reaction to a gene therapy
treatment. This tragic event slows gene therapy
applications and results in greater scrutiny and
caution toward the growing number of gene therapy
research trials.

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1999 The first complete sequence of a human
chromosome (number 22) is completed by the public
genome project and is published. This step
indicates that the genome project is proceeding
ahead of schedule, and also shows a surprisingly
small number of genes (about 300) relative to the
anticipated 100,000 or so for all twenty-four
human chromosomes (twenty-two chromosomes called
autosomes shared equally by males and females,
plus the X-chromosome which is paired in females
but occurs in a single copy in males, plus the
Y-chromosome that is unique to males).

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2000 Celera sequences the genome of the
fruitfly (Drosophila melanogaster), identifying
approximately 13,000 genes among 170 million
nucleotides. First plant genome sequenced
(Arabidopsis thaliana) from the mustard family.
The Arabidopsis genome consists of about 100
million nucleotides, and approximately 20,000
genes, indicating that at the molecular genetic
level, plant and animal genomes are about equally
complex.

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2000 "Golden rice," a genetically engineered
strain of rice manufactures its own vitamin A.
Golden rice is created by Ingo Potrykus, plant
geneticist, and his colleagues to help alleviate
severe health problems in many areas of the world
caused by vitamin A deficiency.
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2001 In mid-February, the journal SCIENCE
publishes an analysis of the Celera Human Genome
Project, and the journal NATURE publishes an
analysis of the public Human Genome Project.
Both revealed a surprisingly small number of
human genes, estimated jointly at about 30,000 to
35,000, barely more than a worm, fruitfly, or
plant. Both show that only about 2 percent of
our DNA actually codes for amino acid sequences
of proteins, and both identify many sequences of
unknown function and variable length present in
multiple copies making up approximately half the
genome.

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Extraction
Each human cell has enough DNA to code for all
the traits in the human body. If the DNA in one
cell was stretched out, how long would it be? Do
the math! There are 6 X 109 base
pairs/cell Each base pair is 0.34 X 10-9 meters
long
Answer 2 meters
A human body has approximately 75 trillion cells.
If the distance to the sun is 150 X 109 meters,
how many round trips could your DNA make?
Answer 500 trips
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Extraction
DNA from kiwi fruit