The Molecule Essays - DNA, Genetics, Nucleic Acids,

The Molecule In the autumn of 1951, James Watson (left) and Francis Crick (right) started work on unravelling the structure of DNA. It was known at the time that DNA was present in the nucleus of every living cell, and that it had something to do with heridity, but without a knowledge of its structure little more could be understood about how it actually worked. They approached the problem with the same methodology that had been pioneered by Linus Pauling, who after years of exhaustive study had earlier discovered that many proteins exhibited a helical structure. Their task was to devise a structure which would account for all the chemical and X-ray evidence, and at the same time be consistent with all the structural features of the units involved - such as the size and shape, bond angles and lengths, configurations and conformations. X-ray diffraction photographs of DNA fibres taken by Rosalind Franklin and Maurice Wilkins showed a distinctive X-shape, which was characteristic of a helix structu re, but strong arcs on the meridian indicated a repeating structure 3.4 ? apart. And from the chemical evidence, it was known that part of the structure was comprised of 4 heterocyclic bases, adenine (A), guanine (G), cytosine (C) and thymine (T), somehow linked together with sugar units and phosphates. One of the biggest puzzles was that although the proportion of these bases varied from one DNA to another, it was always found that the number of A = T, and G = C. Adenine Guanine Cytosine Thymine The 4 bases which make up DNA (Click on each image to get its 3D molfile). Using molecular models, Watson and Crick devised a structure in which all of the building blocks fitted together without crowding or overlapping, and which permitted a great deal of stabilisation by Hydrogen bonds. Moreover, these Hydrogen bonds were of the kind that Pauling had shown to be the strongest and therefore the most important for determining structure in proteins, namely N-H-N or N-H-O. In April 1953 Watson and Crick published their structure - the now famous double helix. This brilliant accomplishment ranks as one of the most significant discoveries in science because it led the way to an understanding of genetics in terms of the molecules involved. In 1962 they received the Nobel prize for Medicine in recognition of this achievement, along with Maurice Wilkins of Kings College London who had performed the initial X-ray crystallography studies. A very small section of DNA showing the double helix structure linked by bases, like the rungs on a twisted ladder. (Click here or on the image to get 3D structure in Molfile format). (Click here to get an interactive 3D structure in pdb format - requires Chime). Bases, Nucleotides and Nucleosides In every living cell there are found nucleoproteins - substances made up of proteins combined with natural polymers, the nucleic acids. Where the backbone of a protein molecule is a polyamide (or polypeptide) chain, the backbone of a nucleic acid molecule is a polyester chain (called a polynucleotide chain). The ester is derived from phosphoric acid (the acid portion) and a sugar (the alcohol portion). Polynucleotide chain The sugar is D-ribose, which is in the group of nucleic acids called ribonucleic acids (RNA), and D-2-deoxyribose forms the basis of DNA. The 2-deoxy simply indicates the lack of an -OH group at the 2 position. Thus DNA stands for deoxyribonucleic acid. Attached to the carbon at one side of the sugar is one of the 4 bases, A, C, G, or T. The base-sugar unit is called a nucleoside. Attached to the other side of the sugar is a phosphoric acid unit, linking the nucleoside to the neighbouring sugar. The base-sugar-phosphoric acid unit is called a nucleotide. Adenosine, a nucleotide containing adenine (red), deoxyribose (black) and phosphoric acid (blue). The 3D molfiles of all of the 4 nucleotides can be obtained here: A, C, G, T. Two of these polynucleotide chains, which can be many millions of nucleotides long, then wrap around one another to form the double helix structure, with every A group H-bonding to the T group on the adjacent chain (see here for A-T molfile), and every G group H-bonding to its matching C group (see here for G-C molfile). DNA - the source of

Pythagoras of Samos Biography

Pythagoras of Samos Biography Pythagoras, a Greek mathematician and philosopher, is best known for his work developing and proving the theorem of geometry that bears his name. Most students remember it as follows: the square of the hypotenuse is equal to the sum of the squares of the other two sides. Its written as: a 2 b2 c2. Early Life Pythagoras was born on the island of Samos, off the coast of Asia Minor (what is now mostly Turkey), about 569 BCE. Not much is known of his early life. There is evidence that he was well educated, and learned to read and play the lyre. As a youth, he may have visited Miletus in his late teenage years to study with the philosopher Thales, who was a very old man, Thaless student, Anaximander was giving lectures on Miletus and quite possibly, Pythagoras attended these lectures. Anaximander took a great interest in geometry and cosmology, which influenced the young Pythagoras. Odyssey to Egypt The next phase of Pythagorass life is a bit confusing. He went to Egypt for some time and visited, or at least tried to visit, many of the temples. When he visited Diospolis, he was accepted into the priesthood after completing the rites necessary for admission. There, he continued his education, especially in mathematics and geometry. From Egypt in Chains Ten years after Pythagoras arrived in Egypt, relations with Samos fell apart. During their war, Egypt lost and Pythagoras was taken as a prisoner to Babylon. He wasnt  treated as a prisoner of war as we would consider it today. Instead, he continued his education in mathematics and music and delved into the teachings of the priests, learning their sacred rites. He became extremely proficient in his studies of mathematics and sciences as taught by the Babylonians. A Return Home Followed by Departure Pythagoras eventually returned to Samos, then went to Crete to study their legal system for a short time. In Samos, he founded a school called the Semicircle. In  about 518 BCE, he  founded another school in Croton (now known as Crotone, in southern Italy). With Pythagoras at the head, Croton maintained an inner circle of followers known as mathematikoi (priests of mathematics). These mathematikoi lived permanently within the society, were allowed no personal possessions and were strict vegetarians. They received training only from Pythagoras, following very strict rules.  The next layer of the society was called the akousmatics. They lived in their own houses and only came to the society during the day.  The society contained both men and women.   The Pythagoreans were a highly secretive group, keeping their work out of public discourse. Their interests lay not just in math and natural philosophy, but also in metaphysics and religion. He and his inner circle believed that souls migrated after death into the bodies of other beings. They thought that animals could contain human souls. As a result, they saw eating animals as cannibalism.   Contributions Most scholars know that Pythagoras and his followers didnt study mathematics for the same reasons as people do today. For them, numbers had a spiritual meaning. Pythagoras taught that all things are numbers and saw mathematical relationships in nature, art, and music. There are a number of theorems attributed to Pythagoras, or at least to his society, but the most famous one,  the Pythagorean theorem, may not be entirely his invention. Apparently, the Babylonians had realized the relationships between the sides of a right triangle more than a thousand years before Pythagoras learned about it. However, he spent a great deal of time working on a proof of the theorem.   Besides his contributions to mathematics, Pythagorass work was essential to astronomy. He felt the sphere was the perfect shape. He also realized the orbit of the Moon was inclined to Earths equator, and deduced that the evening star (Venus) was the same as the morning star. His work influenced later astronomers such as Ptolemy and Johannes Kepler (who formulated the laws of planetary motion). Final Flight   During the later years of the society, it came into conflict with supporters of democracy. Pythagoras denounced the idea, which resulted in attacks against his group. Around 508 BCE, Cylon, a Croton noble attacked the Pythagorean Society and vowed to destroy it. He and his followers persecuted the group, and Pythagoras fled to Metapontum. Some accounts claim that he committed suicide. Others say that Pythagoras returned to Croton a short time later since the society was not wiped out and continued for some years. Pythagoras may have lived at least beyond 480 BCE, possibly to age 100. There are conflicting reports of both his birth and death dates. Some sources think he was born in 570 BCE and died in 490 BCE.   Pythagoras Fast Facts Born: ~569 BCE on SamosDied: ~475 BCEParents: Mnesarchus (father), Pythias (mother)Education:   Thales, AnaximanderKey Accomplishments:  first mathematician Sources Britannica: Pythagoras-Greek Philosopher and MathematicianUniversity of St. Matthews: Pythagoras BiographyWikipedia Edited by Carolyn Collins Petersen.