Lesson 1: The History Flashcards
Phoebus Levene (1910) p1
An american biochemist, isolated two diffferent types of nucleic acids that could be distinguished by the sugars involved in their composition.
-One contained the sugar ribose whch he termed ribonucleic acid
-the other contained an unknown sugar that was similar to ribose but was missing an oxygen atom, therefore he called it deoxyribose and termed the nucleic acid as deoxyribonucleic acid
showed the DNA and RNA were composed of long chains of nucleotides
Phoebus Levene p2
Levene also discovered the structure of a nucleotide:
a phosphate group, a pentose sugar and one of five nitrogenous bases
—nucleotides make up DNA
—Levene concluded equal amounts of e/ base must be present in a chain of nucleic acid.
Phoebuus Levene p2 - nitrogenous bases in DNA
Adenine, Thymine, Guanine and Cytosine
—Thymine is replaced by Uracil in RNA
DNA structure: The sugar
In DNA the sugar is called deoxyribose, this is a pentose sugar because it contains 5 carbon atoms
DNA structure: Phosphate Group
The acidic part of the nucleotide, connects the 5’ carbon of one nucleotide to the hydroxid (-OH) group on the 3’ carbon of the neighbouring nucleotide
DNA structure: Nitrogenous Bases
The nucleotide is named for the nitrogenous base attached.
There are 4 bases found in DNA:
1. Purine : Adenine and Guanine
2. Pyrimidines: Thymine and Cytosine
Purines
The nitrogenous bases that have a double-ringed structure
Pyrimidines
The nitrogenous bases that have a single-ringed structure
Fred Griffith (1928), Oswald Avery (1944)
Experiments suggest that DNA is the “genetic” material.Due to Griffith’s investigation thatinvolved transforming factors in pneumococcus bacteria in mice.
- Griffith was killed during World War II before confirming the transforming factorsand publishing his findings.
-Avery proposed DNA as the transformative component, building on Griffith’s findings.
Alfred Hershey and Martha Chase (1953)
The “Blender Experiment” included tagging bacteriophages with radioactive isotopes and blending them with non-radioactive E. Coli bacteria. Only radioactively tagged viral DNA was transmitted to E. Coli, indicating that DNA serves as the cell’s transforming factor/genetic material.
Erwin Chargaff - Chargaff Ratio’s (1952)
Chargaffbelieved DNA was more than just the repeated tetranucleotide blocks outlined by Levine. It was observed that the number of adenine bases was always equal to the number of thymine bases, whereas the number of cytosines was always equal to the number of guanines. However, the quantity of adenines and thymines did not always match the amount of cytosines and guanines.
Rosalind Franklin and Maurice Wilkins
(1952 – 1953)
Franklin was an expert in X-ray crystallography.
The researcher used X-ray crystallography to create two sets of X-ray photographs of DNA, indicating a helical shape. However, they were unable to determine how the nucleotides fit into this stable configuration.
-Wilkins shared one batch of X-ray photos with another group of scientists.
-Franklin died from cancer in 1953.
James Watson and Francis Crick (1953)
Identified the structure of DNA using Franklin and Wilkins’ X-ray pictures and Pauling’s method.The proposed DNA structure was a double helix.
A base pairing approach using hydrogen and covalent bonds;confirmingChargaff’s ratios.The DNA strands of the double helix were found to be “anti-parallel” (meaning they ran in opposing directions).
DNA p1
DNA is a threaad-like molecule made up of 2 long strands of nucleotides bound together in the shape of a double helix
If the helix was unwound it would look like a “ladder”
DNA p2: The Sugar—Phosphate Backbone
would be the “rails” and are held together by covalent bonds
