Brief History of DNA Flashcards
What did Friedich Miescher discover in 1869?
He isolated phosphorus rich chemicals which he named nucleins (nucleic acids) from the nuclei of white blood cells.
Miescher believed that they were for storing phosphorus.
How did Miescher isolate the nucleic acids?
He treated pus (white blood cells) with a mild alkali and this caused the nuclei to precipitate. From this he then isolated a mixture of DNA and protein which identified to be rich in phosphorus.
what did Phoebus Levene discover?
He showed that there were two types of nucleic acids, DNA and RNA. He aslo identified the parts that made up DNA as phosphate, a deoxyribose sugar and a nitrogenous base. Levene showed that there were four types of DNA nucleotide differing by the nitrogenous base - A,T,C,G. He wrongly believed that these different nucleotides where in equal amounts and also thought this too simple as there were 20 amino acids and only four types of nucleotide.
What did Frederick Griffith discover in 1928?
That Streptococcus pneumoniae can be transformed from the rough (R) phenotype to the smooth (S) phenotype. This ability to pneumoniae had to interchange between strains was put down to an unidentified transforming factor which was later discovered to be DNA.
What did Avery, Macleod and McCarty discover?
They showed that DNA was responsible for the transformation of bacteria into different strains (R and S). At the time it was believed that proteins were the carrier of genetic information and they disproved this.
What did Alfred Hershey and Martha Chase discover using a kitchen blender?
They proved that DNA was the carrier of genetic information as they were still many sceptics after Avery, Macleod and Mcarty’s experiment. They did this by labelling bacteriophages with radioactive phorphorus (for DNA) and radioactive sulphur (for amino acids). These phages then infected bacteria which were left to divide. The progeny of the bacteria showed phorphorus but no sulphur.
What did Erwin Chargaff discover in the 1950s?
He purified human, yeast, bacteria and cow DNA and estimated from chemical analysis the different compositions of the nucleotides (A,T,C,G). This supported the idea that DNA was the hereditary material as the different organisms had diferent amounts of the bases. He also showed that roughly in each species that amounts of A=T and amounts C=G.
What was the model of DNA that Linus Pauling proposed and how did Watson and Crick know that it was incorrect?
He proposed that DNA was a triple helix, with three PARALLEL strands and the bases on the outside. However Crick knew that this was wrong as this would mean the phosphate groups would face in towards each other and there negative charge meant they would repel.
What model did Watson and Crick propose?
They suggested that DNA was a double helix with its two strands being anti parallel. The antiparallel strands allowed for a constant pitch and turn of the DNA molecule. Also Chargaff’s rules were explained by saying that A bonded to T and C bonded to G by hydrogen bonds. (3 for C-G and 2 for A-T).
