He claims not that the discovery of the structure of DNA constituted an examplar of how science is done, but that it was not atypical. In The Double Helix, Watson attempts to demonstrate that the factors that influence scientific discovery are more than genius and hard work; friendships, personality clashes, and luck all play a part, and so do aesthetic considerations. Science is a profession with relatively little in the way of material prizes. Its principal rewards are acclaim by fellow practitioners and the immortality provided by the eternal linkage of a scientist with his or her discovery.
Garland Science ; DNA was known to be a long polymer composed of only four types of subunits, which resemble one another chemically.
Early in the s, DNA was first examined by x-ray diffraction analysis, a technique for determining the three-dimensional atomic structure of a molecule discussed in Chapter 8. The early x-ray diffraction results indicated that DNA was composed of two strands of the polymer wound into a helix.
The observation that DNA was double-stranded was of crucial significance and provided one of the major clues that led to the Watson-Crick structure of DNA.
Only when this model was proposed did DNA's potential for replication and information encoding become apparent.
In this section we examine the structure of the DNA molecule and explain in general terms how it is able to store hereditary information. Hydrogen bonds between the base portions of the nucleotides hold the two chains together Figure As we saw in Chapter 2 Panelpp.
In the case of the nucleotides in DNA, the sugar is deoxyribose attached to a single phosphate group hence the name deoxyribonucleic acidand the base may be either adenine Acytosine Cguanine Gor thymine T.
Because only the base differs in each of the four types of subunits, each polynucleotide chain in DNA is analogous to a necklace the backbone strung with four types of beads the four bases A, C, G, and T. These same symbols A, C, G, and T are also commonly used to denote the four different nucleotides—that is, the bases with their attached sugar and phosphate groups.
Figure DNA and its building blocks. DNA is made of four types of nucleotides, which are linked covalently into a polynucleotide chain a DNA strand with a sugar-phosphate backbone from which the bases A, C, G, and T extend.
A DNA molecule is composed of two more The way in which the nucleotide subunits are lined together gives a DNA strand a chemical polarity. The three-dimensional structure of DNA —the double helix —arises from the chemical and structural features of its two polynucleotide chains.
Because these two chains are held together by hydrogen bonding between the bases on the different strands, all the bases are on the inside of the double helix, and the sugar -phosphate backbones are on the outside see Figure In each case, a bulkier two-ring base a purine ; see Panelpp.
This complementary base-pairing enables the base pairs to be packed in the energetically most favorable arrangement in the interior of the double helix. In this arrangement, each base pair is of similar width, thus holding the sugar-phosphate backbones an equal distance apart along the DNA molecule.
To maximize the efficiency of base-pair packing, the two sugar-phosphate backbones wind around each other to form a double helix, with one complete turn every ten base pairs Figure Figure Complementary base pairs in the DNA double helix. The shapes and chemical structure of the bases allow hydrogen bonds to form efficiently only between A and T and between G and C, where atoms that are able to form hydrogen bonds see Panelpp.
Figure The DNA double helix. A A space-filling model of 1. Each turn of DNA is made up of The coiling of the two strands around more The members of each base pair can fit together within the double helix only if the two strands of the helix are antiparallel —that is, only if the polarity of one strand is oriented opposite to that of the other strand see Figures and A consequence of these base-pairing requirements is that each strand of a DNA molecule contains a sequence of nucleotides that is exactly complementary to the nucleotide sequence of its partner strand.
The Structure of DNA Provides a Mechanism for Heredity Genes carry biological information that must be copied accurately for transmission to the next generation each time a cell divides to form two daughter cells.
Two central biological questions arise from these requirements:Double Helix Readers Guide * Max Perutz – was the head of the unit where Crick works at Cambridge University.
Perutz also shared important X-ray crystallography imagery with Watson and Crick that he had received from Maurice Wilkins and Franklin.
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Sample Essay. Words Double Helix was written by James Watson in , almost fifteen years after of discovery and six years after getting the Nobel Prize.
Double Helix is a fiction, mystery novel. It’s about an eighteen year old boy named Eli Samuels, who has a lot going for him: athletic skill, intelligent mind, and the . get even a better essay. we will write a custom essay sample on the double helix. specifically for you. order now! James Watson accounts all the events of his career that occurred during to , which led to the discovery of structure of the DNA in his famous piece of science writing called “The Double Helix”.