Download Themes in the Development of DNA Science

Themes in the Development
of DNA Science
A short history of Molecular
Biology
Ancient Wine Server
Biotechnology is not new
Production of bread, beer and
wine along with cheese and yogurt
predate modern record keeping
X-Ray crystallography
Max Delbruck: The intellectual
father of molecular biology
He and other quantum physists
applied the principles of physical
science research to biology and
made molecular biology into a
rigorous discipline
You must know how moleculs
react in a test tube in order to
understand how they respond in
vivo.
William Harvey (1640)
Demonstrates that organs work together as a system to
circulate blood in the body
Linus Pauling uses X-ray crystallography to deduce the structure of
proteins
April 25th 1953
Biotechnology
begins
formally
James Watson and
Francis Crick
demonstrate their
model of the DNA
molecule
Swedish biologist Carl Linnaeus
Set up a hierarchy for classifying
living things
Charles Darwin
The publication in 1869 of Darwin’s
Origin of the Species marked the
first step in the biological revolution
that culminated a century later in
Watson’s and Crick’s structure of
DNA
1) There is a natural selection, over great periods of time, for the “fittest”
forms of life.
2) 2) Natural selection arises from the competition for limited food and other
resources among members of the same species. Only the fittest
members of the population survive to reproduce.
3) 3) On rare occasions, a random physical change increases an
individual’s ability to adapt to environmental conditions and/or exploit
new food resources. This “adaptive” changge increases the individual’s
chances to survive and to reproduce.
4) Adaptive changes are passed on to offspring as part of their hereditary
endowment. These individuals are, in turn, fitter that their peers and
survive to pass on their physical characteristics to succeeding
generations.
5) Through the process of adaptive radiation, populations of organisms
evolve to exploit specialized food resources, thus limiting competion and
increasing chances for survival.
Gregor Mendel
Mendel’s paper published in
1865 provided the basis for
the mathematical analysis of
inheritance. From the results
of controlled crosses of
garden peas, he showed that
traits are inherited in a
predictable manner as
discrete bits of genetic
information, or “factors”
Mendels Laws:
Law of Segregation
Parental genes for each trait segregate so that each sex cell
contains only one sort. Thus, each contrasting member of a
gene pair is equally likely to occur in gametes: C or cand P or p
Law of Independent Assortment
Genes for different traits assort into gametes independent of one
another. Thus, each combination of genes is equally likely to
occur: CP. Cp, cP or cp
Mendel’s work lay
unrecognized until 1900 when
Hugo de Vries rediscovered
Mendel’s paper and published
research data that proved his
work.
Walter Suttonc 1902
He was the first to study
chromosome behavior.
This formed the basis of
Chromosome theory
Direct evidence to support chromosome theory was
shown by Edmund Wilson. He showed that sex is
determined by separate X and Y chromosomes.
Femaleness is characterized by two copies of the x (XX)
and maleness to a single x and a single y (XY)
Thomas Hunt Morgan
Established the lowly Fruit fly as the
organism of choice for genetic
research
The random appearance of a single
male white eyed fruit fly established
forever the importance of an observable
mutation or variation from the norm, as
the starting point for genetic research.
Edward Tatum
George Beadle
Use mold and induced mutations to show genes mediate cellular chemistry
Fred Griffith and his mouse experiment
Oswald Avery
His experiment clearly showed that DNA
was the hereditary molecule but
scientists of the time dismissed his work
because DNA was too “simple” to be the
source of genetic variation.
Hershey Chase Experiment
Hershey Chase experiment
1) Most of the phage DNA remains with the bacterial cells.
2) Most of the phage protein is found in the supernate fluid.
3) Most of the initially infected bacteria (in the cell pellet) remain competent to
produce phage.
4) If thew mechanical stirring is omitted, both protein and DNA sdediment with
the bacteria
5) The phage protein removed from the cells by stirring constantly consists of
more or less intact, empty phage coats, which may therefore be thought of
as passive vehicles for the transport of DNA from cell to cell and having
performed that task, play no further role in phage growth.
The physical arrangement of
atoms within DNA was made
possible the development of Xray crystallography pioneered by
Linus Pauling
It was Rosalind Franklin’s Xray crystallography that
ultimately showed the
structure of DNA
Watson and Crick did not
acknowledge her
contribution and she did not
receive the Nobel Prize.
She died from the radiation
exposure incurred in her
research
Arthur Kornberg
Discovered the enzymatic mechanism
of DNA replication
He purified an enzyme from E, coli,
called DNA polymerase I
He found that synthesis only occurs in
the presence of a DNA template
How Does DNA Structure
describe Protein Synthesis?
1) The sequence hypothesis stated that DNA sequence and
protein sequence are colinear. Genetic information must
therefore be arrayed in a strickly loinear fashion along thwe
length of the DNA molecule
2) The “central dogma” stated that gwentic information
stored in DNA flows through RNA to proteins. RNA is the
intermediate translator of the genetic code.
Cracking the Code
Marshall Nirenberg cracks the
genetic code in 1966
By producing polypeptides in vitro
they confirmed that the DNA code
is in triplet form
Ammendments to the Central
Dogma
1) Some organisms do not use DNA as the storage molecule for
the genetic code. RNA viruses store genetic info as RNA
Genes are not immutably fixed on the chromosomes.
Transposable genetic elements move around from one
chromosome to another and may act as molecular switches to
regulate gene expression.
DNA sequence and protein sequence are not entirely colinear. The
RNA transcript is often extensively editted prior to protein
synthesis
RNA has catalytic abilities previously attributed only to proteins.
Self-replicating RNMA may have preceded DNA in molecular
evolution.
Depending on precisely hwere transcription begins, a single DNA
sequence can be read in several overlapping “reading frames” of
codons, which may translate into different polypeptides.