Deoxyribonucleic acid DNA is a molecule that carries most of the genetic instructions used in the development, functioning and reproduction of all known living organisms and many viruses. DNA is a nucleic acid; alongside proteins and carbohydrates, nucleic acids are one of the three major macromolecules essential for all known forms of life. DNA stores biological information and is involved in the expression of traits in all living organisms.
At the time, other scientists like Linus Pauling and Maurice Wilkins were also actively exploring this field. Pauling had discovered the secondary structure of proteins using X-ray crystallography. One extremely important result of his discovery was that it helped James D.
They reasoned that because adenine and thymine always exist in the same proportion, they must always bond together, and similarly for cytosine and guanine. This conclusion led them to propose a double helix structure for DNA, for which they won the Nobel Prize in Their model showed DNA as consisting of two strands of sugar and phosphate alternating on each strand with the pyrimidine and purine bases attached to each sugar component and bonding the two strands together.
Though his main interest lay in the living cell and he liked to think of himself as a naturalist philosopher, Chargaff did research in many areas of biochemistry.
He did a lot of work with lipids, the molecules that form fats, and in particular studied the role of lipid-protein complexes in the metabolism. He also did work with thromboplastic protein, the enzyme biological catalyst that initiates blood coagulation. Chargaff received honorary degrees from Columbia University and the University of Basel in A member of many scientific societies including the National Academy of Science, he was a visiting professor in numerous universities around the world.
In his later years Chargaff eschewed scientific research and turned to writing. He gained popularity in Europe for his prize-winning essays and "doomsday" lectures. He mourns most emphatically the loss of "excellent science" in modern society. In a interview for Omni Magazine Chargaff emphasized his dismay at the contemporary evolution of scientific research into a modern commercial commodity.
He repeatedly denied any bitterness in being overlooked for the Nobel Prize, despite the fact that his discoveries laid the cornerstone for the work of Watson and Crick. He rejected further any comparison between their work and his own. Department of Health, Education and Welfare. In other words, the precise geometries and dimensions of the double helix can vary. The most common conformation in most living cells which is the one depicted in most diagrams of the double helix, and the one proposed by Watson and Crick is known as B-DNA.
There are also two other conformations: A-DNA , a shorter and wider form that has been found in dehydrated samples of DNA and rarely under normal physiological circumstances; and Z-DNA, a left-handed conformation.
Z-DNA was first discovered in , but its existence was largely ignored until recently. Watson and Crick were not the discoverers of DNA, but rather the first scientists to formulate an accurate description of this molecule's complex, double-helical structure. Moreover, Watson and Crick's work was directly dependent on the research of numerous scientists before them, including Friedrich Miescher, Phoebus Levene, and Erwin Chargaff.
Thanks to researchers such as these, we now know a great deal about genetic structure, and we continue to make great strides in understanding the human genome and the importance of DNA to life and health. Chargaff, E. Chemical specificity of nucleic acids and mechanism of their enzymatic degradation. Experientia 6 , — Dahm, R. Human Genetics , — Levene, P. The structure of yeast nucleic acid. Ammonia hydrolysis. Journal of Biological Chemistry 40 , — Rich, A.
Zhang, S. Z-DNA: The long road to biological function. Nature Reviews Genetics 4 , — link to article. Watson, J. A structure for deoxyribose nucleic acid.
Nature , — link to article. Wolf, G. Chemical Heritage 21 , , 37—41 Restriction Enzymes. Genetic Mutation. Functions and Utility of Alu Jumping Genes. Transposons: The Jumping Genes. DNA Transcription. What is a Gene? Colinearity and Transcription Units.
Copy Number Variation. Copy Number Variation and Genetic Disease. Copy Number Variation and Human Disease. Tandem Repeats and Morphological Variation. Chemical Structure of RNA. Eukaryotic Genome Complexity. RNA Functions. Pray, Ph. Citation: Pray, L.
Nature Education 1 1 The landmark ideas of Watson and Crick relied heavily on the work of other scientists. What did the duo actually discover? Aa Aa Aa. Figure 1: The chemical structure of a nucleotide. A single nucleotide is made up of three components: a nitrogen-containing base, a five-carbon sugar, and a phosphate group.
The nitrogenous base is either a purine or a pyrimidine. Of Avery's work, Chargaff wrote the following: "This discovery, almost abruptly, appeared to foreshadow a chemistry of heredity and, moreover, made probable the nucleic acid character of the gene Figure 2: What is Chargaff's rule? These features are as follows: DNA is a double-stranded helix, with the two strands connected by hydrogen bonds.
A bases are always paired with Ts, and Cs are always paired with Gs, which is consistent with and accounts for Chargaff's rule. Most DNA double helices are right-handed; that is, if you were to hold your right hand out, with your thumb pointed up and your fingers curled around your thumb, your thumb would represent the axis of the helix and your fingers would represent the sugar-phosphate backbone. The DNA double helix is anti-parallel, which means that the 5' end of one strand is paired with the 3' end of its complementary strand and vice versa.
As shown in Figure 4, nucleotides are linked to each other by their phosphate groups, which bind the 3' end of one sugar to the 5' end of the next sugar. Not only are the DNA base pairs connected via hydrogen bonding, but the outer edges of the nitrogen-containing bases are exposed and available for potential hydrogen bonding as well. These hydrogen bonds provide easy access to the DNA for other molecules, including the proteins that play vital roles in the replication and expression of DNA Figure 4.
Figure 4: Base pairing in DNA. Two hydrogen bonds connect T to A; three hydrogen bonds connect G to C. The bottom four base pairs are shown flattened instead of twisted, so this region can be easily seen in a cut-away showing a close-up view. The cut-away shows the individual atoms and bonds in the DNA molecule.
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