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What is DNA?
DNA stands for deoxyribonucleic acid and is the hereditary material that is present in almost every cell in the human body (besides red blood cells) and almost all other organisms. The name describes the molecule's structure. "Deoxy" means "missing an oxygen atom" and ribo tells us this oxygen atom is missing in the ribose sugar part of the nucleotide. DNA is an acid because of the phosphate groups that give the molecule acidic properties. DNA holds instructions for development, functioning and reproduction of the living organism.
DNA stands for deoxyribonucleic acid and is the hereditary material that is present in almost every cell in the human body (besides red blood cells) and almost all other organisms. The name describes the molecule's structure. "Deoxy" means "missing an oxygen atom" and ribo tells us this oxygen atom is missing in the ribose sugar part of the nucleotide. DNA is an acid because of the phosphate groups that give the molecule acidic properties. DNA holds instructions for development, functioning and reproduction of the living organism.
The Hereditary Material Debate
Friedrich Miechner was a Swiss biochemist who, in 1869, discovered a material in the nuclei of pus cells. He called this material nuclein and proposed that this was in fact the cell's hereditary material. Prior to this discovery proteins were thought to be the hereditary material. The protein vs. nuclein debate continued into the 20th century. Hershey and Chase are credited for ending the debate in 1952 when DNA was accepted as the hereditary material passed on from parent cell to daughter cell. In their experiement bateriophages (composed of DNA and protein) were used to infect bacterial hosts. Isotopes and radioisotopes of sulfur and phosphorus were used to track the virus. Hershey and Chase noted that only DNA entered the cell and it was in fact responsible for carrying and passing on any genetic information.
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Building a Model for DNA Structure
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Linus Pauling
Pauling was an American biochemist who proposed a triple helix as the structure of DNA. One of the crucial mistakes he made in creating this model was that it gave phosphorus a valence of 6 instead of the correct 5. In his model the phosphates formed a core of the helix and bases pointed outwards. His model provided some valuable information that aided in the correc model being built.
Pauling was an American biochemist who proposed a triple helix as the structure of DNA. One of the crucial mistakes he made in creating this model was that it gave phosphorus a valence of 6 instead of the correct 5. In his model the phosphates formed a core of the helix and bases pointed outwards. His model provided some valuable information that aided in the correc model being built.
Rosalind Franklin & Maurice Wilkins
Franklin was an English chemist and Wilkins was an English physicist and molecular biologist. They worked together at King's College in London where Franklin and assistant, Raymond Gosling, created the famous x-ray crystallography image of DNA. From this she determined some basic dimensions of DNA strands and that the phosphates were arranged on the outside. This image and information was brought to Watson and Crick by Wilkins and helped confirm their suspicions of a double helical structure. Wilkins published the findings from his lab in 1953, in the same issue that Watson and Crick published theirs.
Franklin was an English chemist and Wilkins was an English physicist and molecular biologist. They worked together at King's College in London where Franklin and assistant, Raymond Gosling, created the famous x-ray crystallography image of DNA. From this she determined some basic dimensions of DNA strands and that the phosphates were arranged on the outside. This image and information was brought to Watson and Crick by Wilkins and helped confirm their suspicions of a double helical structure. Wilkins published the findings from his lab in 1953, in the same issue that Watson and Crick published theirs.
James Watson and Francis Crick
With the groundwork layed out by a number of different pioneers in DNA exploration, Watson and Crick were able to piece together the pieces of the puzzle. They were the first to propose an accurate description of the complex structure of DNA and create a 3D model of the double helix. The pair used different materials to piece together a model, making changes and improvements as new information arose. They published their findings in Nature in 1953.
Watson, Crick and Wilkins won the Nobel Prize in Physiology or Medicine in 1962 for their contributions to determining the structure of deoxyribonucleic acid.
With the groundwork layed out by a number of different pioneers in DNA exploration, Watson and Crick were able to piece together the pieces of the puzzle. They were the first to propose an accurate description of the complex structure of DNA and create a 3D model of the double helix. The pair used different materials to piece together a model, making changes and improvements as new information arose. They published their findings in Nature in 1953.
Watson, Crick and Wilkins won the Nobel Prize in Physiology or Medicine in 1962 for their contributions to determining the structure of deoxyribonucleic acid.
Addressing Misconceptions
- That Watson and Crick "discovered" DNA : Watson and Crick are two key players in the journey of understanding the structure of DNA, however they did not discover DNA. A number of different people and experiments have gone into building our understanding of the organic material and it continues to grow.
- note that Watson and Crick did not discover DNA, Miechner was the one to discover the substance and name it nuclein.
- they were the two to first create a model that correctly represents the structure of DNA.
- introduce all of the key players in the journey to discovering the role of DNA. Explain that like many other discoveries, there are a number of different people working towards finding more pieces to the puzzle. The people given credit are often those who can put together all the pieces first.
- That Rosalind Franklin took Photo 51: Although Franklin's impressive work with x-ray crystallography at King's College made the creation of this image possible, it was actually Raymond Gosling that created the famous x-ray diffraction image known as Photo 51. Rosalind was Gosling's academic advisor.