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DNA mystery

Creeth was born in 1924 and educated at the local Northampton County Grammar school. He stayed in England’s East Midlands to read chemistry at what was then University College Nottingham, and after graduation undertook his PhD under the chemists J. Masson Gulland and Denis O. “Doj” Jordan, who helped Creeth reach his groundbreaking conclusions.

At that time there was growing interest in DNA because scientists suspected it might be the substance associated with genes or inheritance. Research had shown it was made from sections known as nucleotides. Each contained a sugar residue known as deoxyribose, a phosphate-group molecule and one of four different types of nitrogen-group molecules or “bases”: thymine (T), cytosine (C), adenine (A) and guanine (G).

But how the DNA molecule was constructed and held together, and how it recorded our genes remained a mystery. Some scientists even (incorrectly) thought it might take the shape of a ball. If they could work out its exact structure, they might be able to reveal the secrets of the genetic code. Creeth’s fellow students, C.J. Threlfall and H.F.W. Taylor had already made inroads. Threlfall had worked out how to purify a sample of DNA so it could be examined for clues about the structure. Gulland, Jordan and Taylor then studied the purified DNA using a process called electrometric titration to follow how its pH changed as they added acid or alkali. When they didn’t get the results they expected, they thought it might have been caused by the presence in the DNA structure of hydrogen bonds. These occur when hydrogen atoms share electrons with certain other atoms including oxygen and nitrogen, and can affect the overall shape of the molecule. The final and definitive step was made in an experiment by Creeth using a technique know as viscometry. This provides a measure of the size of the DNA molecule in solution and how the size can change. When a strong acid or alkali was added to the solution, its “viscosity” or thickness (resistance to flow) dramatically dropped, which indicated the presence of hydrogen bonds. Creeth, Gulland and Jordan concluded that the hydrogen bonds joined the bases of neighbouring nucleotides. The acid or alkali irreversibly disrupted these bonds to break down the DNA molecule into smaller units and make the solution much runnier. Though Creeth and his supervisors never quite managed to make the final step of working out the exact structure of DNA, they did manage to show hydrogen bonds must be an important part of the molecul DNA mystery Creeth was born in 1924 and educated at the local Northampton County Grammar school. He stayed in England’s East Midlands to read chemistry at what was then University College Nottingham, and after graduation undertook his PhD under the chemists J. Masson Gulland and Denis O. “Doj” Jordan, who helped Creeth reach his groundbreaking conclusions. At that time there was growing interest in DNA because scientists suspected it might be the substance associated with genes or inheritance. Research had shown it was made from sections known as nucleotides. Each contained a sugar residue known as deoxyribose, a phosphate-group molecule and one of four different types of nitrogen-group molecules or “bases”: thymine (T), cytosine (C), adenine (A) and guanine (G). But how the DNA molecule was constructed and held together, and how it recorded our genes remained a mystery. Some scientists even (incorrectly) thought it might take the shape of a ball. If they could work out its exact structure, they might be able to reveal the secrets of the genetic code. Creeth’s fellow students, C.J. Threlfall and H.F.W. Taylor had already made inroads. Threlfall had worked out how to purify a sample of DNA so it could be examined for clues about the structure. Gulland, Jordan and Taylor then studied the purified DNA using a process called electrometric titration to follow how its pH changed as they added acid or alkali. When they didn’t get the results they expected, they thought it might have been caused by the presence in the DNA structure of hydrogen bonds. These occur when hydrogen atoms share electrons with certain other atoms including oxygen and nitrogen, and can affect the overall shape of the molecule. The final and definitive step was made in an experiment by Creeth using a technique know as viscometry. This provides a measure of the size of the DNA molecule in solution and how the size can change. When a strong acid or alkali was added to the solution, its “viscosity” or thickness (resistance to flow) dramatically dropped, which indicated the presence of hydrogen bonds. Creeth, Gulland and Jordan concluded that the hydrogen bonds joined the bases of neighbouring nucleotides. The acid or alkali irreversibly disrupted these bonds to break down the DNA molecule into smaller units and make the solution much runnier. Though Creeth and his supervisors never quite managed to make the final step of working out the exact structure of DNA, they did manage to show hydrogen bonds must be an important part of the molecule

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