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DNA
The Code of Life
The Molecular Basis
of Inheritance
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.
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.
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.
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?
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 gene—one 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.
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 wasn’t 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.
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 wasn’t considered to
be smart enough to code for all of life!
History
Search for genetic material:
1928 Frederick Griffith: transforming principle
History
Search for genetic material:
It wasn’t 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 Avery’s 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
Avery’s work.
History
Search for genetic material:
1952 - Hershey-Chase Experiment
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
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.
The Discovery
The seed that generated this was Watson’s
presence at a conference in Naples in 1951,
where an x-ray diffraction picture from
DNA was shown by Maurice Wilkins from
King’s College in London.
This made a strong impression on Watson –
the first indicationthat genes might have
a regular structure.
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 King’s.
Watson attended a DNA colloquium there in November 1951, at
which Rosalind Franklin described her results.
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.
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 King’s and Wilkins
showed him a DNA x-ray pattern taken by Franklin of the pure Bform 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 King’s
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.
History
Search for genetic material:
Watson began pursuing the idea of hydrogen bonding using
cardboard cutouts of the four bases. He found that (A+T)
and (G+C) could be bonded together to form pairs with very
similar shapes. On this basis a model was built consistent with
the symmetry and with Chargaff’s results, and a paper was
published in April 1953 in Nature accompanied by ones from
the Wilkins and Franklin groups at King’s. Watson and Crick’s
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”.
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
Watson and Crick with their
DNA model
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.
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.
Watson & Crick
What they deduced from:
Franklin’s X-ray data
• Double helix
• Uniform width of 2 nm
• Bases stacked 0.34 nm apart
Chargoff’s “rules”
• Adenine pairs with thymine
• Cytosine pairs with guanine
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
KEY PLAYERS
Oswald Avery (1877-1955)
Microbiologist 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.
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".
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.
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.
.
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.
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.
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.
Structure
Structure
Structure
Structure
Structure
Structure
There are 4 different nucleotides in DNA
Adenine pairs with Thymine
Guanine pairs with Cytosine
Structure
Adenine pairs with Thymine
Guanine pairs with Cytosine
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
Bases can change through
incorporating stable changes known mechanisms
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.
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.
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.
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
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
1972
- Paul Berg
Produces first recombinant DNA
using EcoRI
1973
-Boyer, Cohen & Chang
Transform E. coli with
Recombinant plasmid
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.
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
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 Huntington’s
disease is developed using
restriction fragment length markers.
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
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.
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.
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
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
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.
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.
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
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.
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 Ychromosome that is unique to males).
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.
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.
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.
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
Extraction
DNA from kiwi fruit