The discovery of dna
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The Discovery of DNA. Friedrich Miescher. Began working with white blood cells in 1869. White blood cells are a major component of pus in infections. As a result, Miescher collected a lot of pus from bandages at a local hospital. .

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The Discovery of DNA

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The Discovery of DNA


Friedrich Miescher

  • Began working with white blood cells in 1869.

  • White blood cells are a major component of pus in infections. As a result, Miescher collected a lot of pus from bandages at a local hospital.

  • Added a weak alkaline solution to the white blood cells– when he did the cells decomposed and caused the nuclei to move out of the solution.

  • From the nuclei, Miescher isolated a substance known as “nuclein”

  • After chemical analysis, nuclein was later renamed as DNA.


Frederick Griffith

  • In the 1920s he was trying to develop a vaccine for pneumonia.

  • Began to wonder if a strain of bacteria could transform into another strain.

  • He took two strands of pneumococcus bacteria (deadly strain [III-S] and non-deadly strain [II-R]) and injected them into healthy mice.

  • Firstly, he found that when injected with the deadly strain (III-S) the mice died, and when injected with the non-deadly strain (II-R), the mice survived.


Frederick Griffith

  • Secondly, he heated up the deadly strain (III-S) to kill the bacteria and when injected into the mice, they did not die.

  • Lastly, he co-injected the heated deadly strain (III-S) with the non-deadly strain (II-R) and when injected into the mice, they died.

  • He concluded that some “principle” transformed the non-deadly strain (II-R) into a deadly strain (III-S).

  • He called this the “transforming principle”


“Transforming Principle”

Rough strain: II-R (non-deadly strain)

Smooth strain: III-S (deadly strain)

Third Experiment

Second Experiment

First Experiment


..

Joachim Hammerling

  • In the 1930s, began experimenting with Acetabularia, a form of green algae.

Cap

  • He found that when you removed the cap, it grew back, but if you removed the foot, it would not grow back.

Stalk

  • This showed that the instructions for making the cap were in the foot (which was where the nucleus was).

  • He concluded that the nucleus contained DNA, and was responsible for development.

Foot


Oswald Avery, Maclyn McCarty and Colin McLeod (1944)

  • Was interested in the work that Frederick Griffith did.

  • What was the “principle” that transformed the non-deadly strain (II-R) into a deadly strain (III-S).

  • They discovered that it was DNA, not protein that was responsible for transformation.


Erwin Chargaff

  • In 1949, he began experimenting with DNA.

  • He isolated DNA from different organisms and measured the levels of adenine, guanine, thymine and cytosine. These were his results:


Chargaff’s Rule

  • Levene’s tetranucleotide theory stated that adenine, guanine, cytosine, and thymine would equal each other.

  • However, Chargaff concluded that the nucleotides must be arranged in a way that adenine and thymine are equal and that cytosine and guanine are equal (A=T/C=G).


DNA Structure Was Discovered

  • Through the work of Miescher, Griffith, Hammerling, Avery, McCarty, McLeod and Chargaff, the structure of the nucleotide was discovered.

  • The structure of the nucleotide included: pentose sugar attached to a phosphate group at carbon 5 and a nitrogenous base at carbon 1.


Alfred Hershey and Martha Chase

  • Conducted an experiment in 1952 on bacteriophage (viruses that attack and infect bacteria).

  • Using radioactive isotopes, Hershey and Chase traced the movement of DNA and protein during phage infection.

  • They showed that DNA, not protein entered the bacterial cell during phage reproduction and that only DNA was passed on to phage offspring.

  • This concluded that DNA, not protein carries the genetic material of the cell.


Rosalind Franklin

  • Began researching the structure of DNA in the early 1950s.

  • Franklin used X-ray diffraction (a technique used to examine the shape and structure of a molecule) to take a picture of a DNA molecule.

  • The picture showed the double helical structure of DNA. However, the picture shows the DNA molecule from the end, not the side.


James Watson, Francis Crick and Maurice Wilkins (1953)

  • Wilkins passed on the photo that Franklin had taken to Watson and Crick.

  • Using Franklin’s photo and Chargaff’s rule, Watson and Crick were able to explain and prove the double helical structure of DNA.

  • Using Chargaff’s data, they were able to come up with the “complementary base pairing” in DNA where a purine (A/G) always binds with a pyrimidine (T/C).


James Watson, Francis Crick and Maurice Wilkins (1953)

  • They proposed that the helix in DNA turned clockwise and was a right handed helix.

  • They concluded that the helix would make a complete turn every 10 nucleotides, which is a distance of 3.4nm, so the space between nucleotides is 0.34nm.

  • Also they discovered that DNA strands run anti-parallel to each other (one strand runs in a 5’ to 3’ direction and the other strand runs 3’ to 5’.)


James Watson, Francis Crick and Maurice Wilkins (1953)

  • For all their research, Watson, Crick and Wilkins won the Noble Peace Prize in 1962.

  • Rosalind Franklin was never given any credit for her discovery, and died in 1958.


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