Waldorf University Discovery of The DNA Double Helix Reflection Paper I need a minimum of 1300 words for this assignment.
USE ONLY THE 3 MENTIONED ARTICLES TO CITE IN THIS PAPER!
need this done in 5 hours!!
be very specific on the topic!
The details are incorporate in the file named HomeWork5.
Basically, we need to write the essay about the “discovery of the DNA double helix reveal about the process of scientific discovery”, Based on the reading “The Double Helix” by James Watson, and other few resourses provided below, but no other outside resources.
The essay need to be 4-5 pages, double spaces.
Also for the third resource, please check out this youtube link. https://www.youtube.com/watch?v=uYuo72X46pA&t=1s Rosalind Franklin
and the Double Helix
1957, she had published an additional
dozen articles on carbons other than
coals. Her papers changed the way
physical chemists view the microstructure of coals and related substances.
Franklin made many friends in
the Paris laboratory and often hiked
with them on weekends. She preferred
to live on her own modest salary and
frustrated her parents by continually refusing to accept
money from them. She excelled at speaking French and at
French cooking and soon became more comfortable with
intellectual and egalitarian “French ways” than with conventional English middle-class customs. Consequently,
she did not fit in well at King’s College, where she worked
on DNA from 1951 to 1953. Franklin chose to leave King’s
and, in the spring of 1953, moved to Birkbeck College.
Many of the students there were evening students who
worked during the day, and Franklin was impressed with
their dedication. After the move to Birkbeck, she began her
celebrated work with J. Desmond Bernal on RNA viruses
like tobacco mosaic virus (TMV). She was a cautious scientist who began to trust her intuition more as she matured (see box 1 on page 45). She published 14 papers
about viruses between 1955 and 1958, and completed the
research for three others that colleague Aaron Klug submitted for publication after her death.
In his obituary for Franklin, Bernal described her as
a “recognized authority in industrial physico-chemistry.”
In conclusion, he wrote, “As a scientist, Miss Franklin was
distinguished by extreme clarity and perfection in everything she undertook. Her photographs are among the most
beautiful of any substances ever taken.”1
Although she made essential contributions toward elucidating the structure of DNA, Rosalind Franklin is known to
many only as seen through the distorting lens of James
Watson’s book, The Double Helix.
Lynne Osman Elkin
1962, James Watson, then at Harvard University, and
University’s Francis Crick stood next to MauWilkins from King’s College, London, to receive the
Nobel Prize in Physiology or Medicine for their “discoveries concerning the molecular structure of nucleic acids and
its significance for information transfer in living material.”
Watson and Crick could not have proposed their celebrated
structure for DNA as early in 1953 as they did without access to experimental results obtained by King’s College scientist Rosalind Franklin. Franklin had died of cancer in
1958 at age 37, and so was ineligible to share the honor.
Her conspicuous absence from the awards ceremony—the
dramatic culmination of the struggle to determine the
structure of DNA—probably contributed to the neglect, for
several decades, of Franklin’s role in the DNA story. She
most likely never knew how significantly her data influenced Watson and Crick’s proposal.
Franklin, shown in figures 1 and 2, was born 25 July 1920
to Muriel Waley Franklin and merchant banker Ellis
Franklin, both members of educated and socially conscious
Jewish families. They were a close immediate family,
prone to lively discussion and vigorous debates at which
the politically liberal, logical, and determined Rosalind excelled: She would even argue with her assertive, conservative father. Early in life, Rosalind manifested the creativity and drive characteristic of the Franklin women,
and some of the Waley women, who were expected to focus
their education, talents, and skills on political, educational, and charitable forms of community service. It was
thus surprising when young Rosalind expressed an early
fascination with physics and chemistry classes at the academically rigorous St. Paul’s Girls’ School in London, and
unusual that she earned a bachelor’s degree in natural sciences with a specialty in physical chemistry. The degree
was earned at Newnham College, Cambridge in 1941.
From 1942 to 1946, Franklin did war-related graduate work with the British Coal Utilization Research Association. That work earned her a PhD from Cambridge in
1945, and an offer to join the Laboratoire Central des Services Chimiques de l’Etat in Paris. She worked there, from
1947 to 1950, with Jacques Mering and became proficient
at applying x-ray diffraction techniques to imperfectly
crystalline matter such as coal. In the period 1946–49, she
published five landmark coal-related papers, still cited
today, on graphitizing and nongraphitizing carbons. By
Lynne Elkin (email@example.com) is a professor of biological
sciences at California State University, Hayward. She welcomes
responses and inquiries about issues pertaining to the story of
Rosalind Franklin and DNA structure.
Discovery of two forms for DNA
Franklin’s most famous and controversial work yielded critical data that Watson and Crick used to determine DNA’s
structure. DNA is a double-helical molecule roughly in the
form of a spiral staircase. The double-helical molecule, consisting of two unbranched polynucleotide chains, is best visualized by imagining it straightened into a ladder. The side
rails of the ladder are each made up of alternating sugar
and phosphate groups, linked by so-called 3⬘ or 5⬘ phosphodiester bonds. The sequence of the atoms in each rail runs
in opposite directions, so the two sides of the molecular
backbone are often described as antiparallel to each other.
The rungs of the ladder consist of specific hydrogen-bonded
horizontal pairs of nitrogenous bases that are attached to
the deoxyribose sugars in the backbone’s side rails. Birkbeck’s Sven Furberg, who studied both the nucleoside and
nucleotide of one of the bases, cytosine, in 1949, discovered
that the base would be perpendicular to the sugar: The result can be extrapolated to hydrated DNA.2
The pairs of nitrogenous bases that make up the rungs
are in the keto, as opposed to enol, tautomeric configurations. (The two are distinguished by the locations of hydrogen atoms available for hydrogen bonding.) The smaller single-ringed pyrimidines, cytosine (C) and thymine (T), are
always paired with larger double-ringed purines, guanine
(G) and adenine (A). Indeed, the consistent pairing of G with
C and of A with T, as first proposed by Watson, explains the
© 2003 American Institute of Physics, S-0031-9228-0303-020-5
Figure 1. The Tuscan landscape forms the background
of this photograph of Rosalind Franklin, taken in the
spring of 1950 by her friend
Vittorio Luzzati. (Courtesy of
identical size of the ladder rungs and also Erwin Chargaff ’s
1952 observation that G and C (and likewise A and T) are
always present in DNA in approximately equal amounts.
The consistent pairings, along with the irregular linear vertical sequence of the bases, underlie DNA’s genetic capacity.
In an experiment carried out shortly after she arrived
at King’s, Franklin identified two distinct configurations,
called by her the A and B forms, in which DNA could exist.
Her work, first presented in an internal King’s seminar in
November 1951 and published in Nature in 1953, was essential for determining the structure of DNA. Researchers
working prior to Franklin’s discovery invariably had to
deal with confusing x-ray diffraction patterns that resulted from a mixture of the A and B forms.
The drier crystalline A form contains about 20%
water by weight and is optimally produced at about 75%
relative humidity. Cation (for example, Na⊕) bridges between ionized phosphates are probably responsible for intermolecular linking in the crystalline structure. The less
ordered, fully hydrated, paracrystalline B form—typically
the configuration that occurs in vivo—is obtained from the
crystalline A form when DNA fibers absorb water in excess of 40% of their weight. Optimal production of the B
form occurs at approximately 90% relative humidity.
Extra hydration makes it easier for the molecule to assume the lowest-energy, helical configuration. It also
keeps the two helical backbone chains farther apart than
in the A form and elongates the molecule by about 30%
until the B form appears with its bases oriented perpendicular to the fiber axis.
Franklin slowly and precisely hydrated then dehydrated her DNA sample to obtain her best pictures of the
A form. To get her samples, though, she had to extract DNA
fibers from a gel-like undenatured DNA sample that
Wilkins had acquired from Rudolf Signer of the University
of Berne in Switzerland. Franklin pulled exceptionally
thin single fibers and controlled the humidity in her specimen chamber by bubbling hydrogen gas through salt solutions and then flooding the chamber with the humid gas
that resulted. Franklin’s PhD student, Raymond Gosling,
told me that the chamber leaked so much hydrogen gas
that he was afraid they would blow themselves up accidentally and take half of King’s College with them.
Franklin’s careful treatment during the transformation
from crystalline A-form to hydrated B-form DNA resulted in
such a drastic size change that, according to Gosling, the
elongating specimen practically “leaped off the stage.” After
designing a tilting microfocus camera and developing a technique for improving the orientation of her DNA fibers in the
camera’s collimated beam, Franklin took x-ray diffraction
photographs of the B form.
Franklin’s B-form data, in conjunction with cylindrical Patterson map calculations that she had applied to her
A-form data, allowed her to determine DNA’s density,
unit-cell size, and water content. With those data,
Franklin proposed a double-helix structure with precise
measurements for the diameter, the separation between
each of the coaxial fibers along the fiber axis direction,
and the pitch of the helix.3
The resolution of the B-form photograph #51 shown
in figure 3 allowed Franklin to determine that each turn
of the helix in the B form is 34 Å long and contains 10 base
pairs separated by 3.4 Å each,3 in accordance with less precise data obtained by William Astbury and Florence Bell
in 1938.4 Wilkins, photographing living sperm cells in
1952, obtained an X-shaped B-form diffraction pattern
Figure 2. Coffee served in crucibles
was a tradition in Jacques Mering’s
Paris laboratory, where Rosalind
Franklin worked from 1947 to 1950.
Biographer Anne Sayre reports that
the time Franklin spent working in
Paris was the happiest period of her
life. This candid photo was taken by
Vittorio Luzzati. (Courtesy
of Vittorio Luzzati.)
similar to Franklin’s. Her photograph,
though, showed much more detail.
The cylindrical Patterson map calculations that Franklin applied to the Aform of DNA were the first such calculations applied to any molecule.
They confirmed her suggestions that
the hydrophilic sugar phosphates form
the external backbone of the DNA molecule and that the hydrophobic base
pairs are protected inside that backbone from the cell’s aqueous environment. The calculations also allowed her to deduce that the
A-form helix has two antiparallel chains (see figure 4d).
With Gosling, Franklin provided details of the physical
distortion accompanying the dehydration transformation
from B-form to A-form DNA.5 She also showed that the
bases of the A form are tilted and curved slightly, and that
11 pairs of bases are compacted within a repeat distance
of 28.1 Å.
In her section of the 1952 King’s Medical Research
Council (MRC) report, Franklin gave quantitative measurements for the interphosphate distances and discussed
the external placement of the phosphates. Her presentation was instrumental in getting Watson and Crick to
abandon their earlier attempts at placing the bases on the
outside of their model. Initially, they (and Linus Pauling,
too) mistakenly thought that the bases would have to be
externally accessible in order to pass genetic information.
In May 1952, Franklin presented her clearest evidence
of the helical backbone, with her diffraction photograph
#51. Although she did not yet realize how the nitrogenous
bases are paired or that the helical backbone rails of B-form
DNA are antiparallel, her notebook entries starting in January 1951 clearly show that she was making significant
progress toward solving those two final aspects of DNA
structure. After reading an article by June Broomhead,6
and studying other related papers, she had used the keto
configuration for at least three of the four bases. She was
aware both of Jerry Donohue’s work concerning tautomeric
forms of bases and of Chargaff ’s work (see figure 4).
Astbury and Bell’s earlier, less clear diffraction photographs and later data of Wilkins suggested some of the
data that Franklin derived from her photograph #51. But
Franklin’s results were much more precise than the Astbury and Bell data, which showed neither an X pattern nor
layer lines. Astbury and Bell themselves described their
results as “still rather obscure.” After Oxford crystallographer Dorothy Hodgkin helped her to eliminate two of three
possibilities she had calculated, Franklin described the
correct crystallographic space group for DNA in the 1952
Only after Crick obtained Franklin’s data—his thesis
adviser, Max Perutz, agreed to give him a copy of the 1952
report and Watson had seen photograph #51—was he sufficiently convinced to start constructing the backbone of
the successful DNA model. He recognized the similarity of
the space group Franklin had calculated to that of his thesis molecule, hemoglobin, and immediately deduced that
there would be an antiparallel orientation between the two
DNA coaxial fibers. Within one week, he started modeling
the correct backbone in a manner compatible with
Franklin’s data. On several occasions, Crick has acknowledged that the data and conclusions in the 1952 report
Franklin’s 17 March 1953 draft
On 18 March 1953, Wilkins penned a letter acknowledging
receipt of the Watson and Crick manuscript that described
the structure of DNA. A day earlier, Franklin, who was
preparing to leave for Birkbeck, polished an already written draft manuscript outlining her conclusions about the
double-helix backbone chain of B-form DNA.7 Franklin only
slightly modified her draft to prepare her April 1953 Nature paper, which appeared as the third in a series that led
off with the famous Watson and Crick proposal. Partly as
a consequence of its placement, Franklin’s paper seemed
merely to support Watson and Crick’s work. But Franklin’s
data played far more than just a supporting role—as early
as 1968, Watson’s The Double Helix tells us so.
Ironically, despite its negative portrayal of Franklin,
The Double Helix was what first brought widespread attention to Franklin’s key contributions to the Watson and
Crick proposal. The book describes how Watson and Crick
built their first, and incorrect, model right after Watson
inaccurately reported Franklin’s November 1951 seminar
data to Crick. It also details how, after 13 months of inactivity, they built their correct model once Wilkins showed
Franklin’s photograph #51 to Watson, and Perutz showed
Crick the 1952 MRC report.
The importance of Franklin’s work to the discovery of
DNA structure has not been well documented until recently for a variety of reasons too long to discuss here. Relevant issues include women’s being underrepresented in
historical accounts, although several authors have striven
to correct that imbalance;8 Watson and Crick’s routinely
citing the more senior Wilkins before Franklin;
and Wilkins’s repeating much of Franklin’s
work. In addition, Wilkins, not Franklin, was
nominated for membership in the Royal
Society even though, at the time of his nomination, Franklin was famous for her TMV
Conflict within the King’s MRC
Box 1. The Evolution of Franklin’s Intuition
very scientist I interviewed, except James Watson and Max Perutz,
agreed that Rosalind Franklin was a superb scientist with the sharp
mind and vision needed to plan, execute, and analyze a good experiment. Questions about her capabilities have centered on her ability to
make intuitive leaps when interpreting results, mainly because she
seemed hesitant to do so in her DNA work. Franklin often expressed the
opinion that the facts should speak for themselves. Her desire to have
solid proof for her ideas before publishing them helps explain her highly
successful publication record. She argued that a scientist need not be
highly speculative, which gave the impression that she was incapable of
Franklin’s manner and scientific approach while at King’s College,
London were uncannily close to those described by Frederick Dainton,
Franklin’s physical chemistry don when she was an undergraduate at
Cambridge University. Writing to biographer Anne Sayre, Dainton says
that “he was attracted by [Franklin’s] directness . . . including the way
she defended her point of view, something she was never loath to do.”
Dainton found Franklin to be a “very private person with very high personal and scientific standards, and uncompromisingly honest. . . . She
once told me the facts will speak for themselves, but never fully accepted my urging that she must try to help the receptor of her messages. . . . As you point out, the logical sequential arguments meant
everything to Rosalind. . . .”13
Francis Crick has suggested that Franklin’s aversion to speculative
thinking about DNA excludes her from the rank of the great scientists. He
has noted, though, that the problem might not have been that Franklin
lacked intuition, but rather that she might not have trusted it. Moreover,
Crick has suggested that Franklin’s intuition seemed to be rapidly improving as she matured as a scientist while working with tobacco mosaic
virus. And if Franklin did not trust her intuition while working on DNA,
it may have been at least partially because she did not have anyone at
King’s with whom she could properly discuss her ideas.
Franklin was an outstanding and accomplished
scientist—a fascinating individual with a
strong personality who made a lasting impression on almost everyone she met. Throughout
her career, she routinely ate lunch amicably
with both male and female colleagues and most
of her acquaintances liked her. Her numerous
lifelong friends thought her bright, fascinating,
witty, and fun. Most of her lunchtime colleagues at King’s would agree with that description, but only as it pertained to her
lunchtime persona. When Rosalind headed for
the laboratory, she shed almost every vestige of
lightheartedness as she focused exclusively on
Furthermore, in what amounted almost to
social heresy in England, en route to her laboratory she typically bypassed the morning coffeepot and afternoon tea in favor of a direct assault on her work. Franklin was considered by
King’s colleagues to be “too French” in her
dress, in her intellectual interests, and in her
temperament. She was exceedingly direct, intent, and serious, with the tendency to leap into
passionate debate. She could be assertive,
uniquely stubborn, argumentative, and abrasive to the point that colleagues, especially Wilkins, sometimes found her unpleasant.
On the rare occasions when Franklin departed from
her typical behavior, King’s colleagues usually did not even
notice—they took her seriously at all times. That became
especially important when she created a “death of the
helix” funeral invitation as a joke after obtaining some
data indicating that A-form DNA is nonhelical (see box 2
on page 46).
Whereas Franklin was quick, intense, assertive, and
directly confrontational, Wilkins was exceedingly shy, indirect, and slowly calculating to the point of appearing
plodding. Almost all testimony from King’s staff indicates
that any blame for th…
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