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Structure of nucleic acids
Friederich Miescher, swiss physician and biologist, discovers the genetics material from white blood cell nuclei. He noted it had an acidc nature and called it nuclein. -
Discovery of the DNA Components (1900-1910)
Phoebus Levene, a Lithuanian-American biochemist determinate the different components of DNA that are: adenine, guanine, thymine, cytosine and deoxyribose phosphate. He also defined phosphate-sugar-base units called nucleotides. -
Levene's Tetranucleotide
Levene proposed that there were four nucleotides per molecule, and that this made such a simple structure that it couldn't possibly be the key to unlocking heredity. Unfortunately, he was incorrect on both of those counts. DNA could not store the genetic code because it was chemically far too simple. -
Frederick Griffith (1879-1941)
Frederick Griffith was a bacteriologist who studied the epidemiology and pathology of two strains of Streptococcus pneumoniae, and he was the first person to actually demonstrate bacterial transformation in January 1928. -
Griffith's transformation experiment (Part 1)
Griffith used two strains of Streptococcus. The first one called Type S, S is for smooth. These smooth colonies make a capsule, which make the bacteria virulent and deadly. There's also a strain Type R, R is for rough, which is non-virulent or harmless. So they do not have a smooth capsule. -
Griffith's transformation experiment (Part 2)
If you inject the rough strait in a mouse, nothing will happen, instead if you inject smooth strait in a mouse, this will die. If you heat-killed the smooth strain, so you kill the bacteria first, the mouse will live. And if you mix the rough strain and the heat-killed smooth together, the mouse dies. So there's a transformation that took place. The rough strain was transformed in some way by the heat-killed sooth strain. The question was "How this happens?" but Griffith did not figure this out. -
Avery, MacLeod and McCarty Part 2
One group was mixed with a protease. A protease destroys protein. The other one was mixed with a DNase, which destroys DNA. They took the non-virulent strain. They mixed it with the heat-killed smooth virulent strain. Once got the protease, inject into the mouse, this died. The other group was mixed with the DNase injected into mice, the mice live. This showed that it was the DNA that was responsible for the transformation because if you chop up the DNA with the DNase it's not virulent any more. -
Avery, MacLeod and McCarty (Part 1)
This question was answered by three people: Orwals Avery, a Canadian Physician (1877-1955); Colin MacLeod, a Canadian-American Geneticist (1909-1972) and Maclyn McCarty, an American Geneticist. Their experiments in 1944 explained Griffith's results. They determined what actually caused the transformation, and they figured this out by taking the live rough and the heat-treated S, just exactly the same has Griffin had done, but they mixed them with one of two enzymes... --> -
Journal of Experimental Medicine
It was published in February 1944, and they were suggested that it is DNA and not protein that may be hereditary material of bacteria, and they propose perhaps in higher organism as well. -
How this DNA look like and how this it work
DNA exist in two forms. The "A" form, which more people were looking at, it was easier to get at, it's dry. Then, the "B" form, which is actually what DNA really looks like inside the cells. Lots of people were looking for a mixture of the two. In 1951, Watson and Crick wrote a paper in which they described DNA as a double helix with sugars and phosphates at the centre and the nucleobases facing the outside
This model was quickly shown to be incorrect, and in fact it made no chemical sense. -
Counting Nucleobases (Part 1)
Erwin Chargaff started counting nucleobases. Chargaff, emigrate to the United States during the Nazi era, and he became a teacher of biochemistry at Columbia University Medical School, and he actually was interested in percentages of the different nucleobases, and he started to noticed something really strange. He looked at different organisms, and he simply measured the amounts of the four bases: adenine, thymine, cytosine and guanine. -
Chagraff's Rules (Part 2)
Chargaff was actually left out of all the big recognition of the discovery of DNA and after the Nobel Prize was awarded, which he got no part in, he became kind of a recluse and spent the rest of his life writing to scientist about why he was excluded. -
Chargraff's Rules (Part 1)
Chargaff did an experiment with different animals and humans, and he found exactly the same results. This came to be known as Chargaff Rules. The amount of Adeline and thymine were always in balance, and the amount of cytosine and guanine, always in balance. Now this was a massive discover, but himself didn't actually realize the importance of these findings. He shared his discovery with Watson and Crick at the Cavendish Lab in Cambridge in 1952, and Watson and Crick actually knew what it meant. -
Hershey-Chase Experiment (Part 2)
The bacteria have its own nuclear material, that’s going to be the host, and then you took bacteriophages labeled one of two ways. Either with radioactive sulfur, and that allowed them to follow the proteins in the phage, or they used radioactive DNA to follow the movement of DNA during the infection. They took the label phages. They would expose them, allow them to infect the bacteria, and then they would separate what was in the bacteria from what was not in the bacteria by centrifugation. -
Harshey-Chase Experiment (Part 4)
All in the fluid outside. Anything that was protein from the fish did not get into the bacterial cells. What about the DNA?
Label the DNA with P32, radioactive phosphorus, and allow the phages to infect, just like before, and then centrifuge and see where the radioactivity ends up, and now all the radioactivity is in the pellet. It’s all in the bacteria, there’s no radioactivity in the fluid on top. -
Hershey-Chase Experiments
Bacteriophages are viruses that infect bacteria, so we call them a bacteriophage or just a phage for short. They are made of either DNA or sometimes RNA, and then the rest of the face is made of proteins. So that’s going to make up the head, the tail and the tail fibres. So what Hershey and Chase did was they used a bacterial cell. You noticed there’s a genome in there of the bacteria. -
Harshey-Chase Experiment (Part 3)
You spin the tubes really fast, and what you get is the supernate, which is the fluid on top, everything outside the cells, and in the pellet, you get the compressed bacterial cells and everything that’s inside. To label the proteins, they used radio-labeled sulfur S35. Now they’re going to be able to follow the proteins and see what happens. They allow them to infect, and then the phase will disengage. The result was no radioactive material inside the pallet. It was all in the supernatant. -
Hershey and Chase Conclusions
Hershey and chase concluded that it was the DNA and not the protein that was the genetic material, and that the only real need for the protein was to sort of serve as packaging, to cover the thing. -
"Triple Helix?" by Linus Pauling
Linus Pauling, who discovered the structure of the alpha helixes and the beta sheets in protein, he came up with a triple helix model, again, with the phosphates and the sugar on the inside and the nucleobases on the outside. He was mostly certain, looking at x-ray crystallography images that were mixtures of both A and B form. That turned to be incorrect. -
X-ray Diffraction Image of DNA Photo 51 by Rosalind Franklin
Rosalind took a lot of amazing photographs of the B form of DNA. She figured out how to see the wet form, the form that exists in cells. This is probably the most famous image that she got. They call it photo 51, and this photo shows very clearly the x in the middle that is the sing of a double helix. Rosalind was a stickler for detail, and she was not prepared to publish this until she finished all her calculations. -
Maurice Wilkins, Watson and Crick, Rosalind Franklin and Photo 51
Maurice Wilkins got Photo 51 from Rosalind's desk in King's College and managed to get it to Watson and Crick in Cambridge. When they saw the image, they knew that their model from 1951 was backwards or inside out. They built the model based on Rosalind's image. In the April 1953, three papers were published, in the edition of the journal "Nature". The first was Watson and Crick paper. The second one was by Stokes and Wilkins. The third was by Rosalind Franklin and her assistant, Raymond Gosling -
The nobel prize in Physiology or Medicine 1962
The reason why Rosalind Franklin did not share in the Nobel Prize was because, unfortunately, she had already passed away, and the Nobel Prize are only given to living people. Neither of the three acknowledge the importance of her work in their discovery. Many people have come to think that they were the ones responsible for the discovery because their article was listed first, and that Franklin was merely collaborating. -
DNA is a Double-Stranded Helix
Nowadays, we know that DNA is a Double-Stranded Helix with the backbone made of sugar and phosphate groups running antiparallel. Hydrogen bonds between the nucleobases, A with T and G with C. That explains why they are always in the same amounts.
The sequence of nucleobases codifies the amino acid sequence of a protein. Strings of base pairs that code for a product are called genes