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Discovery of Nucleic Acids
Nucleic acids were discovered in 1869, when the Swiss Friedrich Miescher, that is a Scientific, at the age of 24 years old, isolate the genetic material from white blood cell nuclei. He noted it had an acidic nature and called it nuclein -
Discovery of DNA components
Determined the components of DNA:
- Adenine, guanine, thymine, cytosine, deoxyribose phosphate
- Defined phosphate-sugar-base units called nucleotides -
Levene's Tetranucleotide
Phoebus Aaron Theodore Levene it was a biochemical that they were born on 25 of February 1869, and he dies at 6 of September 1940. Levene proposed that there were four nucleotides per molecule. DNA could not store the genetic code because it was chemically far to simple. -
Frederick Griffith
Frederick Griffith it was a bacteriologist that studied the epidemiology and phatology of two strains. In January 1928 reported the first Widley accepted demonstrations of bacterial transformation. -
Griffith's Transformation Experiment 1
He used two strains of streptococcus, one that is called type S. S is for smooth.These smooth colonies make a capsule, wich make the bacteria virulent, and deadly. So they cause the mice to die. There's also a strain type R, which is non-virulent, and harmless. So they do not have that smooth capsule, and mice when exposed to it, they do just fine. -
Griffith's Transformation Experiment 2
If you take the rough non-virulent strain, inject it to a mouse, no problem. If you take the smooth strain, the virulent strain, inject it to a mouse, and then the mouse die. If you heat kill the smooth strain, you kill first the bacteria, an the mouse will live. If you mix the rough strain and the head-killed smooth strain together, the mouse dies. The question was: how did that happen? -
Avery, MacLeod and McCarty
They was three people that determined the cause of the transformation in Griffith's Experiment, and they figured this out by taking the live rough and the heat-treated S, just exactly the same, as Griffith had done but they mixed them with one of two enzymes. One the group was mixed with a protease. A protease destroys protein. The other was mixed with a DNase which destroys DNA. -
Avery, MacLeod and McCarty Experiment Conclusions
Avery concluded that DNA is the genetic material of the cell. Science is a process in which discoveries are often based on the results of previous experiments. Despite Avery's findings, many scientists remained sceptical that genes were made of DNA rather than protein. -
Counting Nucleobases
Erwin Chargaff was a biochemical teacher that it characterized by counting the Nucleobases.
He actually was interested in percentages of the different Nucleobases. He looked at different organisms, and he measured the amounts of the four bases: Adenine, thymine, cytosine and guanine.
So here's an octopus, and here you notice that the amounts of A and T are almost the same. And the amounts of C and G are almost the same. He prove with other animals and the results are the same. -
Hershey-Chase Experiments 2
They used a bacteria cell. The bacteria, of course, has its own nuclear material and that's going to be the host,and then they 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 labeled phages. They expose them, allow them to infect the bacteria. Later they separate what was in the bacteria fro that wasn't. -
Hershey-Chase Experiments
Bacteriophages are viruses that ifect bacteria. So we call them a bacteriophage or just a phage for sort. They are made of either DNA or sometimes RNA, and then the rest of the phage is made of proteins. So that's going to make up the head and the tail, the tails fibers, kinif of looks like a lunar lander, doesn't it. -
Conclusions of Hershey and Chase
Hershey and Chase they concluded that DNA, not protein, was the genetic material. A protective protein coat was formed around the bacteriophage, but the internal but the internal DNA is what conferred its ability to produce progeny inside bacteria. -
Chargaff's rules
The amount of adenine and thymine were always in balance, and cytosine and guanine the same. He did, however, share his discovery with Watson and Crick at the Cavendish Lab in Cambridge in 1952, and Watson and Crick knew that is a big discovery. 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. -
It's the DNA
The race was to determine the structure of DNA in cells and to determine how it codes for proteins and how it codes for proteins and how it replicates.
DNA exists in two forms:
- Dry form
- Wet form (as DNA exists in cells) -
Double Helix?
Watson and Crick wrote a paper in which they describe 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 -
Triple Helix?
Linus Pauling and Robert Corey proposed a triple Helix as the structure of the DNA. It also certified that is incorrect. -
Final Model of DNA
DNA adopts a double helix shape, like a spiral staircase where the sides are chains of sugars and phosphates connected by "steps", which are the nitrogenous bases.