8/13/2019 PY571_Ezequiel Rodriguez_ Week #6

http://slidepdf.com/reader/full/py571ezequiel-rodriguez-week-6 1/2

About the reading 

James Watson (Biologist) and Francis Crick (Physicist) proposed in 1953 for the first a

time a new model for the structure of DNA, which turned to be the correct one. They received

the Nobel Prize in 1962 “for their discoveries concerning the molecular structure of nucleic

acids and its significance for information transfer in living material”.

In that same time, other models were being proposed. Fraser and Pauling,

defended that the structure of the DNA consisted of 3 intertwined chains. Watson

and Crick refused to believe in this model because of two reasons: the distances

between the molecules were too short in the supposed Van der Waals bonds, and

they believed that the material they were visualizing in the X-Ray diagrams was the

salt, and not the free acid.

In contrast, the model proposed by Watson and Crick established that the

DNA structure consisted in two chains that formed a double-helix shape around thesame axis. These chains were related by a dyad connection, and so, their atoms

would run in opposite directions.

Perpendicular to the axis, there are junctions between the two chains,

these are purine and pirimidine bases (in order for a bond to exist, these junctions

have to be purine-pirimidine). The pairs are Cytosine-Guanine and Adenine-Timine,

this pairing-structure system suggested to the scientists that could led a way for

making copies of it. These both are connected by hydrogen bonds and occupy the

same position along the axis.

It was experimentally proved after that these bases are present in DNA material in

ratio of almost the unity (which supports the Watson and Crick’s model). It was proved as well

that it was very unlikely to build this structure with a ribose sugar instead of using a

deoxyribose sugar.

In the published paper, Watson and Crick mention that in that certain time, the results

obtained in the X-Ray diagrams were not enough to prove the validity of their model, but the

ones they had supported the ideas they were presenting in the document. A couple of months

later, Nature published the paper of the other scientists (Maurice Wilkins and Rosalind

Franklin) that worked independently of them in which X-Ray crystallography led to results thatwere in accordance to what Watson and Crick had predicted.

The impact of this discovery (although in real, the confirmation of the model was done

later on), has led to a completely different understanding of life. Many scientists nowadays

compare the double-helix model with Newton’s gravitational law. This model has helped to

understand lots of processes that take place within cells that involve our genetic material.

A lot of researchers are dedicated to study and find out the very specific function of

each piece of each chain of DNA, how to manipulate it (of course, it is important to take into

account all the experimental techniques that are necessary to work in this field, and how all of

them have been developed, and are being, as time goes by), and deeply understand the role in

each process.

Figure 1. Double-

helix model

proposed by

Watson and

Crick.

8/13/2019 PY571_Ezequiel Rodriguez_ Week #6

http://slidepdf.com/reader/full/py571ezequiel-rodriguez-week-6 2/2

An especial interest, of course, is the application in medicine field, getting to know the

functions of each piece of DNA would open the possibility of manipulate it in order to create

cures for determined sicknesses, such as cancer or others.

One last remarkable feature about the model created by Watson and Crick is its impact

into evolution theories. The double-helix model has provided a way of comparing the geneticroots of the human being with the genetic material of other animals. Some scientists believe

that the complete understanding of genome would give a possible answer to the question of

how did life start existing on our planet?

About the lecture 

In this journal diary I decided to center my writing on the paper because the lecture

was about the issue mentioned in last week’s journal. 

I found very interesting having to possibility to understand from another point of view

the process of transcription in a more profound detail, and especially in a lecture by Roger

Kornberg.

Although I am still expecting to see more about the processes in class, because there

are certain points in which it is difficult to follow explanations (probably due to the lack of

biological background), but I am making an effort to review the basic concepts and probably

after talking about all the topics in class, it will be a lot easier to understand.