راغب السرجانى

الثلاثاء، 29 يونيو 2010

Electricity

Abu Edison incandescent lamps - bright miracle

As small as the genius Thomas Edison, and in one dark nights intensified disease on his mother and the doctor decided that they need surgery but must wait until the morning, it needs to be lit to work, and this was a moment of truth in the life of Thomas Edison, who knew that the lives of the most expensive people it may stop the flame of light, Vstr, Thomas Edison in his diary he must find a way to get light at night is stronger than the light of candles, has these words exist in the diary for years, long before they begin research to come out Bmadzth genius, which marked a turning point in the history of modern civilization.

The beginning of the dream

Accept light bulbs out of commercial interest for a long time, he offered physicist Humphrey Davy in 1810 lamp electric arc, which consists of two rods Mudbpin from coal, and applied to the penis voltage electricity is high, and ignite the electric arc strongly approaching Alqdiban from each other, but this invention he has no commercial value due to the lack of sources of electricity strong. The American Charles Brush invented in 1876, arc lights burning strongly, but it was used to illuminate the main streets just because they have a high volume like zooms, and lighting was so strong, and fit only for a few hours and then burn. In 1877 he visited Edison's first laboratory for the Dynamo, who brought him a new idea to produce a lamp glowing architecture of the press look to the future: (The day will come when we can light all the homes and run all plants by electrical appliances, and just touch of a button to get the light in the darkness). Following this statement under the Edison works with 50 working day and night in Menlo Park to achieve the objective which is believed science is impossible to reach, and focus the search for a wire heat runs a long time, and try Edison minerals and one after the other, use to start a thread of carborundum to give the light of white for ten minutes before the burn, and this is the first incandescent lamp, Edison continued to experiment with metal chrome and platinum.

The first light bulb for Thomas Edison

On October 21, 1879 Breathe Edison sigh of relief, where he put a piece of cotton yarn carburetor into a crystal ball and to benefit from past experiences Try Edison to empty the bottle from the air, and then run a power Vetoahj fuse, and continued attending the lamp by the hour and everyone is minutes waiting for combustion , but he continued, this time for 45 hours before burning, and here cheered for everyone, but Edison told his aides that the lamp as long as the work of this period, it can be illuminated for a hundred hours, has been looking for stuff best to make the fuse, he discovered that bamboo is the best material for this purpose, After years according to the manufacture of wire from a combination of fiber extracted from plants, is still used until the mix today, but it Altanjstin coated metal resistant to heat. Commenting on the Edison lamps laboratory for experimental purposes, and spread the news that the magician has accomplished the miracle, and in the New Year's Eve was attended by three thousand visitors to see the lamps that burned until dawn on the first day in 1880, becoming the name of Abu Edison incandescent lamps. And they became the genius in the next phase to become lights of the right of everyone, continue to work on the electricity sub-central to September 1882, before turning the key main lights 400 lamp at the same time, declaring the end of the era of the saddle and Alotarik and darkness, and the beginning of electricity and light. Says physicist Larsen that stage: (Edison established the scientific method to provide homes with electricity and light after the United States, Europe, the people heard in this great event, the people were Irusselouna, saying: Come enlighten our cities.). The world war broke out between the British and Wilson Swan, who made several unsuccessful offers to incandescent lamps, the first in February 3rd, 1879, but the feelings of competition still quick and Swan joined the Edison Company for the manufacture of lamps (Edison electric lighting and heating). The aim of Edison at this stage is to produce a million lights electric, and this company was a great place to attract talent and skills training, they come out on his hands with a lot of innovation and skill, including the Serbian inventor Nikola Tesla Nikola Tesla.

Thomas Edison (1847 - 1931) American inventor invented the light bulb and about 1093 the invention of another.

Of his statements:

There is always a better way.

There is no substitute for hard work.

Be brave! Shown faith! On the move.

We do not know one-millionth of anything.

Great hopes make great people.

To invent you need a good imagination and a pile of junk.

I'm proud of the fact that I have not invented a weapon kills.

I did not fail but I found ten thousand method does not work.

Genius is one percent inspiration and 99 percent effort.

Discovered 100 ways that do not lead to the invention of the battery and tried 9999 times to make the light bulb.


Lien: Innovations human light bulb

Egypt Atomic Scientists

Samir Naguib


World is Samir Naguib Egyptian nuclear scientist in the forefront of the younger generation of nuclear scientists Arabs, graduated from the Faculty of Science, University of Cairo at an early age, and continued his scientific researches in the corn. For efficiency scientific characteristic has been nominated to the United States of America on a mission, and work under the supervision of professors nature of nuclear physics and the age does not exceed thirty-third, showed a gifted, distinguished and genius substantially during the examination which was prepared in the mid-sixties - during his mission to America - to the extent that it had completed the preparation of the letter before schedule one whole year.
Coincidentally, the University announced "Detroit" America contest for the post of assistant professor in natural science, and provides for the contest more than two hundred nuclear scientist from different nationalities, won by Dr. Samir Naguib, and got a job as assistant professor at the University, began his research study that received the admiration of many Americans, and aroused the concern of the Zionists and the pro-Zionist groups in America. As usual, have been coming to Dr. offers material for the development of research, but particularly after the war in June 1967 felt that his country and his country in need. And designed the world to return to Egypt and booking seats on a flight to Cairo on 13/8/1967.
Once, Dr.. Samir for his views even made him many American requests him not to travel, and offered him the temptation of scientific and multi-material to stay in the United States. But Dr. Samir Najib rejected all temptations offered to him. On the night set for his return to Egypt, has moved the hostile forces of Egypt and the Arab nation, these forces are resolved to destroy the structure of modern Arab scientific Whatever the motives and whatever the results. In the city of Detroit, while he was driving his car, Dr. Samir and high hopes revolve in his mind and his head, dreaming of a return to his homeland for his efforts and his research Alyalmswolin, and then see his family after an absence.
In the road were surprised Dr. Samir Naguib car transfer huge, initially thought to be going on the road like the rest of the cars. Tried to cut in any doubt, veered to the side of the road but found that the car following him. At the moment of tragic rushed the truck and then increased speed and hit a Dr. who crashed his car and died immediately, and began the transport vehicle and accompanying driver disappeared, and under the incident against unknown and lost the Arab nation the great scholar could give his country and his nation a lot in a field of corn


One of the scientists whose bodies were found covered with question marks. He died in January 16, 1950 in a manner very primitive .. Poison.
Wali. Mustafa supervisor first Egyptian to participate in space research, but more importantly it was one of the world's students, Albert Einstein, was one of the key aides in the access to the theory of relativity, and fired on d. Honorable title of "Einstein's Arabs," and "the circumstances of the death of Dr. Supervisor sudden too vague, and was all the circumstances surrounding it indicates that murdered either by a representative of King Farouk, or at the hands of international Zionism, and each reason.
May have a monarchy at that time the Egyptian role in the killing, especially if we know that d. Supervisor had set up a group under the name "Egypt's youth", there were a large number of intellectuals, scientists, students, and was designed to exclude system Farouk monarchy and the Declaration of an independent Arab Republic of Egypt. And news of the group is confidential and news reached the royal palace, which gives the palace an excuse to get rid of d. Mustafa. The World Zionist suffice it to say that their view of the student genius d. Samira Moussa would not differ from their perception of the teacher is the most gifted d. Mustafa supervisor, and played Zionism played a dirty physical liquidation, and was one look at means to get rid of them and their ilk.
And Mustafa supervisor is the world of mathematics and physics is an Egyptian born in 1898. And in 1917 was chosen for a scientific mission for the first time to England. He joined "to" College Nottingham Nottingham, and the Faculty of the "King" in London, where he received a Bachelor of Science with Honours in 1923. And holds a Ph.D (Doctor of Philosophy) from the University of London, in the shortest time permitted by the laws of the Whole.
Has returned to Egypt by order of the ministry, and appointed a teacher at Normal Superior, then traveled back to England and obtained a doctorate of Science D. Sc was the first Egyptian to receive them.
In 1925 he returned to Egypt, and was appointed professor of Applied Mathematics, Faculty of Science, Cairo University, and was awarded the degree of "professor" in 1926 despite the objections of the University Act to grant title to anyone who is less than thirty.
Dr. Ain, "the honorable" Dean of the College in 1936 and was elected to the Deanship of four consecutive times, and was elected in December 1945 as an agent of the University.
Research began, Dr. "Ali honorable" take place in scientific journals, age not more than fifteen years. In the Royal University of King's College London, publishing his first five research on quantum theory, which won two classes for which Ph.D (Doctor of Philosophy) and Dsc. (Doctor of Science).
Dr. supervisor made the first scientific research on finding a measure of the vacuum, where the engineering was vacuum-based theory of the "Oenchen" subject only to the movement of particle moving in a gravitational field.
We have added new theories in the interpretation of radiation from the sun, but the theory of Dr. honorably in the radiation and the speed came back from the most important theories and the cause of his fame and its universality, as demonstrated by Dr. honorable Article radiation in origin and can be considered two for one thing becomes one of the other .. And this theory has paved the world to divert Atomic radiation.
Dr. "to" one of a few who knew the secret break-up of corn and one of scientists who fought to use in the war .. But he was the first new idea is that hydrogen can be made from such a bomb .. But it did not wish to create the bomb Aloidrugenip, which occurred several years after his death in the United States and Russia ..
Research estimates Dr. "Ali honorable" unique in the theories of quantum and atom, radiation, mechanics, dynamics, about fifteen in search .. Has reached drafts of scientific research before his death to about two hundred .. Perhaps the doctor was intended to collect to get the Nobel Prize in Mathematical Sciences.
Was invited by the German scientist Albert Einstein's parent to participate in research relating to the dumping of corn in 1945 Visiting Professor for a year, but he apologized, saying: "In my generation needs to"
D, died. Honorably in the January 16, 1950 poison and conditions became the death of Dr. Supervisor sudden too vague and was all the circumstances surrounding it indicate that he was murdered either by a representative of King Farouk or by the Israeli Mossad and each reason.
May be the monarchy of Egypt at that time a role in the killing, especially if we know that d. Supervisor had assembled the group under the name «Youth Egypt» was a large number of intellectuals, scientists, students and was designed to eliminate system Farouk monarchy and Egypt's declaration of the Republic of independent Arab and news of the order of this Community news secret and went to the Royal Palace, which gives the palace an excuse to get rid of d. Mustafa, The World Zionist suffice it to say that their view of the student genius d. Samira Moussa would not differ from their perception of the teacher is the most gifted d. Mustafa supervisor and played Zionism played a dirty filter and the physical one look at means to get rid of them and their ilk.


Mashad Yahya .. Egyptian nuclear scientist and university professor, he studied in Iraq at the University of Technology Department of Electrical Engineering has witnessed his students and all who knew him, morality, intelligence and science.
Mashad Yahya was born in Egypt in milk in 1932, graduated from the electricity department at the University of Alexandria in 1952, graduated in 1963 Doctoral degree in engineering nuclear reactors from the Soviet Union, where he had obtained a scholarship in 1956.
Upon his return he joined the faculty of nuclear energy Egypt, where he is doing research, he moved to Norway between 1963 and 1964, then returned as an assistant professor, Faculty of Engineering, Alexandria University, and was soon was promoted to "Professor", where he supervised many theses and published more than 50 papers were presented.
After the war in June 1967 have been frozen Egyptian nuclear program, which led to the suspension of nuclear research in the field, and the situation became more difficult for him after the 1973 war with Egypt was diverted energies to other directions.
The signing of Saddam Hussein in the November 18, 1975 nuclear cooperation agreement with France, its impact in attracting scientists insist to Iraq, where they went to work there. The refusal of certain shipments of uranium, France, where he looked in violation of the specification, followed by France insisted on attending in person to France to receive the coordination of uranium.
III was assassinated in June 13, 1980, in room No. 941 Le Meridien Hotel in Paris. And it smashed his skull, authorities had limited the French case against the unknown.
Been accused of being a prostitute he was with France and that his death was against the background of this subject, however, Marie-Claude Madjal Prostitute - (Marie's famous Express) - denied the official version, but it reported that he refused to even talk with them, ignored the story of a prostitute, although they were users major and only in the case of his death and was assassinated after a while. and confirms many of his colleagues that the Mossad was behind the assassination.
In general, ignored most of the Arab media, the official news of his death and some said quickly.
Politics and friendship:
Surprisingly, after the family back brace from Iraq, they'd be doing the funeral of the late, did not attend the funeral of any of the officials or colleagues Faculty of Engineering, but a few numbered, as the Egyptian-Iraqi relations at the time were not so good after the signing of the Camp David. The family and brace coming out of Iraq do not know what to do after the departure of Mashad, but for the pension which the state of Iraq and his behavior was spent on the orders of Saddam Hussein's life (although it stopped after the Gulf War). Pension fraction of Social Affairs, which does not observe the status of the family or the development world at large.
The Egyptian media did not highlight enough the story of the assassination of Mashad, despite their importance. Perhaps the timing of this story is the center of political events, a truck make it less important compared to these events. He remained a brace remained closed, and remained a result of inquiries that the perpetrator is unknown. The brace is one of a series of distinguished Arab scholars who have been liquidated by the Mossad.

Said Mr. Bedier

Killing the world, Said Mr. Bedair, son of the artist by the late Sayed Bedier and had graduated from the Military Technical College and was appointed an officer in the Egyptian armed forces until he reached the rank of colonel and retired colonel, at his request he had received a doctorate from England and then worked in research satellite at the University of the West German and Dear contracted to conduct research for two years
There are reaching young engineer, to surprising results have been published research in all countries in the world, even agree with researchers Americans in October 1988 to conduct research with them, after the end of his contract with the German University and here resented the researchers of the German University and began harassing him and harass him even eliminates the idea of a compact with the Americans
According to his wife that she and her husband and their two sons, they discover during their stay in Germany tampering with the furniture their homes and steal the books of her husband, as a result of feeling worried family decided to return to Egypt, to the pair back to Germany to complete the term of his contract and then returned to Cairo on June 8, 1988 and decided to travel to one of his brothers in Alexandria to complete the research where he was found dead
And his wife confirmed that one of the intelligence behind the assassination of her husband and to affirm that the world is happy monastery reached through advanced research results made it occupies the third level only 13 scientists in the field of specialization is rare in the engineering technology for missile


Samira Moussa
Samira Moussa (March 3, 1917 to August 5, 1952) was born in the village of Great Senbo - Center Zefta Western Province, the first atom scientist nicknamed the Egyptian-Arab and the name of Corey Mays Middle .. It is the first lecturer in the Faculty of Science, Fouad I University, now Cairo University.
Infancy
I learned Samira since childhood to read and write, and preserved parts of the Koran and was fascinated to read newspapers, it enjoys a memory strong position to save the thing as soon as read. And moved her father with his daughter to Cairo to teach and bought some of his money hotel Balhasin even invests in the life of the Cairene. Samira went to school, "Palace of Desire" followed by "primary" school girls supervision "School and is built on the founding and managing the" Prophet Moses "Women's well-known political activist.
Perfect grade
Samira won first prizes in all stages of education, was the first certification guidelines in 1935, did not win the girls in this familiar place at the time where it was not allowed into the examination guidelines of the houses only to change the resolution in 1925 establishing the School of Princess Faiza, first secondary school for girls in Egypt.
Was superior to continued significant impact on the school where the government provides financial aid for the school, which comes out first, pushed the headmistress Prophet Moses to buy a special factory when I heard one day that Samira plans to move to a state school available by the laboratory.
The Nbogha for it had to redraft the government algebra book in the first year of high school, and printed at the expense of her father, and distributed free of charge to colleagues in 1933
Her school
Samira Moussa chose Faculty of Science, although the total was positioned to enter the College of Engineering .. When the security of any girl at that time was to join the Faculty of Arts and there drew the attention of her professor, Dr. Ali supervisor, the first Egyptian Dean of the Faculty of Science. Have been influenced by the directly affected, not only scientifically but also on social aspects of his personality.
Samira Moussa, received a Bachelor of Science and was the first in her class, and appointed the first lecturer, Faculty of Science, thanks to the efforts of Dr. The supervisor, who defended strongly and set to ignore the protests of foreign teachers (English).
I got a Masters degree in the subject of communication warming gases traveled on a mission to Britain, studied by nuclear radiation, and got a doctorate in X-rays and their impact on different materials. Equalization important findings of the completed letter in two years and spent the third year in research related to and received from which to offset significant (not been accepted by the Western world at that time) managed to break cheap metals such as copper and then manufacture the atomic bomb materials may be accessible to everyone, but had not been written scientific books Arabic research findings d. Samira Moussa.
Political interests
It was hoped that Egypt and the Arab world place the middle of this major scientific breakthrough, as it believed that the increased ownership of nuclear weapons would contribute to peace, any State that has adopted the idea of peace must be speaking from a position of strength has lived with the scourge of war and the experiences of the atomic bomb that flattened Hiroshima and Nagasaki in 1945 and drew attention early attention from Israel's possession of weapons of mass destruction and seeking to monopolize nuclear arms in the region.
She founded the Atomic Energy Commission just three months after the announcement of the Israeli state in 1948 and was keen to send missions to specialize in atomic science was its repeated invitations to the importance of nuclear arms, and keep up with the tide of scientific growing and organized the Conference of the Atoms for Peace hosted by the Faculty of Science and attended by a number much of the world's scientists have reached in their search to the equation were not accepted when the Western world, it was - God love her - hoping to harness the atom for the good of humankind and pervades the field of medical treatment where she says: «My wish is that the treatment of cancer with corn, such as aspirin». It also was a member of many scientific committees specialized on top "of the Committee on Energy and the prevention of the atomic bomb, formed by the Egyptian Ministry of Health.
Assassinated
Responded Dr. to an invitation to travel to America in 1951, she had the opportunity to conduct research in the labs University of St. Louis, Missouri, received offers to stay in America but she refused and before returning a few days responded to the invitation to visit nuclear plants on the outskirts of California on August 15, and on the way California high rugged truck suddenly appeared; to hit her car strongly and depositing them in a deep ravine, the driver jumped out and disappeared forever.
The beginning of doubt in the fact that her murder
Investigations showed that the driver was carrying a false name and that the Department did not send one of the reactor to take her, she said in her letters to her father: «If it was in Egypt, such as factory plants located here, I could work the needs of the many». Have commented Mohamed El Zayat Egypt's cultural adviser in Washington at the time that the word (the needs of many) that was meant in its ability to break up the invention of the cheap metal atoms through the thermal conductivity of the gases and then making an atomic bomb, cheap costs.
In her last letter she said: «I was able to visit nuclear plants in America and when I go back to Egypt, I will give to my great services in this field and I'm going to serve the cause of peace», where it was intended to establish a special lab in the pyramids in Giza Governorate
It removed the newspapers on her story and that its case is not closed, though evidence suggests - according to observers - that the Mossad, Israeli intelligence is Aghtaltha, a penalty for attempting to transfer nuclear science to Egypt and the Arab world in the early period.

Nabil Al Kaleny

The story of this very strange world, has disappeared since 1975 until now, this world has been sent by the Faculty of Science at Cairo University to Czechoslovakia to do more research and studies in corn.
Scientific research has uncovered by the IAEA for a great scientific genius I talked about all the Czech newspapers, and then received his doctorate in corn from the University of Prague. On the morning of Monday, 27/01/1975 the phone rang in the apartment where he lived, Dr. Al Kaleny and after the call went out, Dr. no longer so far.
Since the communication was interrupted Dr. with the Faculty of Science, Cairo University, sent the college to the University Czech inquiring about the fate of Dr. Nabil, who was a master modern journalism, the Czech international scientific community, and there were University Czech, and after several messages urgent, Faculty of Science, Cairo University, Czech authorities stated that the world Dr. Al Kaleny out of his home after a phone call did not return to his home.
It is strange that the university learned the news of the Czech and dial-up is where I learned it? Is the Czech contacted the police, if the police told the university administration, the Czech police knew where it is??? But the strange thing is that the Egyptian authorities (in 1975) did not investigate this crime, and constants and the facts of disappearance, we tip the scales in that Dr. was lured into an ambush by the Mossad, then either be killed or subjected to so-called wash brain in order to achieve disable everything in his mind advanced scientific studies and either be in a Western or Israeli prisons or to have been exchanged with some Israeli spies in Egypt after the signing of the treaty "at Camp David."

DNA

(DNA) is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information. DNA is often compared to a set of blueprints, like a recipe or a code, since it contains the instructions needed to construct other components of cells, such as proteins and RNA molecules. The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information.

Chemically, DNA consists of two long polymers of simple units called nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds. These two strands run in opposite directions to each other and are therefore anti-parallel. Attached to each sugar is one of four types of molecules called bases. It is the sequence of these four bases along the backbone that encodes information. This information is read using the genetic code, which specifies the sequence of the amino acids within proteins. The code is read by copying stretches of DNA into the related nucleic acid RNA, in a process called transcription.

Within cells, DNA is organized into long structures called chromosomes. These chromosomes are duplicated before cells divide, in a process called DNA replication. Eukaryotic organisms (animals, plants, fungi, and protists) store most of their DNA inside the cell nucleus and some of their DNA in organelles, such as mitochondria or chloroplasts.[1] In contrast, prokaryotes (bacteria and archaea) store their DNA only in the cytoplasm. Within the chromosomes, chromatin proteins such as histones compact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed.
Properties
DNA is a long polymer made from repeating units called nucleotides.[2][3][4] The DNA chain is 22 to 26 Ångströms wide (2.2 to 2.6 nanometres), and one nucleotide unit is 3.3 Å (0.33 nm) long.[5] Although each individual repeating unit is very small, DNA polymers can be very large molecules containing millions of nucleotides. For instance, the largest human chromosome, chromosome number 1, is approximately 220 million base pairs long.[6]

In living organisms, DNA does not usually exist as a single molecule, but instead as a pair of molecules that are held tightly together.[7][8] These two long strands entwine like vines, in the shape of a double helix. The nucleotide repeats contain both the segment of the backbone of the molecule, which holds the chain together, and a base, which interacts with the other DNA strand in the helix. A base linked to a sugar is called a nucleoside and a base linked to a sugar and one or more phosphate groups is called a nucleotide. If multiple nucleotides are linked together, as in DNA, this polymer is called a polynucleotide.[9]

The backbone of the DNA strand is made from alternating phosphate and sugar residues.[10] The sugar in DNA is 2-deoxyribose, which is a pentose (five-carbon) sugar. The sugars are joined together by phosphate groups that form phosphodiester bonds between the third and fifth carbon atoms of adjacent sugar rings. These asymmetric bonds mean a strand of DNA has a direction. In a double helix the direction of the nucleotides in one strand is opposite to their direction in the other strand: the strands are antiparallel. The asymmetric ends of DNA strands are called the 5′ (five prime) and 3′ (three prime) ends, with the 5' end having a terminal phosphate group and the 3' end a terminal hydroxyl group. One major difference between DNA and RNA is the sugar, with the 2-deoxyribose in DNA being replaced by the alternative pentose sugar ribose in RNA.[8]
A section of DNA. The bases lie horizontally between the two spiraling strands.[11] Animated version at File:DNA orbit animated.gif.

The DNA double helix is stabilized by hydrogen bonds between the bases attached to the two strands. The four bases found in DNA are adenine (abbreviated A), cytosine (C), guanine (G) and thymine (T). These four bases are attached to the sugar/phosphate to form the complete nucleotide, as shown for adenosine monophosphate.

These bases are classified into two types; adenine and guanine are fused five- and six-membered heterocyclic compounds called purines, while cytosine and thymine are six-membered rings called pyrimidines.[8] A fifth pyrimidine base, called uracil (U), usually takes the place of thymine in RNA and differs from thymine by lacking a methyl group on its ring. Uracil is not usually found in DNA, occurring only as a breakdown product of cytosine. In addition to RNA and DNA, a large number of artificial nucleic acid analogues have also been created to study the proprieties of nucleic acids, or for use in biotechnology
Grooves
Twin helical strands form the DNA backbone. Another double helix may be found by tracing the spaces, or grooves, between the strands. These voids are adjacent to the base pairs and may provide a binding site. As the strands are not directly opposite each other, the grooves are unequally sized. One groove, the major groove, is 22 Å wide and the other, the minor groove, is 12 Å wide.[13] The narrowness of the minor groove means that the edges of the bases are more accessible in the major groove. As a result, proteins like transcription factors that can bind to specific sequences in double-stranded DNA usually make contacts to the sides of the bases exposed in the major groove.[14] This situation varies in unusual conformations of DNA within the cell (see below), but the major and minor grooves are always named to reflect the differences in size that would be seen if the DNA is twisted back into the ordinary B form.
Base pairing
Each type of base on one strand forms a bond with just one type of base on the other strand. This is called complementary base pairing. Here, purines form hydrogen bonds to pyrimidines, with A bonding only to T, and C bonding only to G. This arrangement of two nucleotides binding together across the double helix is called a base pair. As hydrogen bonds are not covalent, they can be broken and rejoined relatively easily. The two strands of DNA in a double helix can therefore be pulled apart like a zipper, either by a mechanical force or high temperature.[15] As a result of this complementarity, all the information in the double-stranded sequence of a DNA helix is duplicated on each strand, which is vital in DNA replication. Indeed, this reversible and specific interaction between complementary base pairs is critical for all the functions of DNA in living organisms.
The two types of base pairs form different numbers of hydrogen bonds, AT forming two hydrogen bonds, and GC forming three hydrogen bonds (see figures, left). DNA with high GC-content is more stable than DNA with low GC-content, but contrary to popular belief, this is not due to the extra hydrogen bond of a GC base pair but rather the contribution of stacking interactions (hydrogen bonding merely provides specificity of the pairing, not stability).[16] As a result, it is both the percentage of GC base pairs and the overall length of a DNA double helix that determine the strength of the association between the two strands of DNA. Long DNA helices with a high GC content have stronger-interacting strands, while short helices with high AT content have weaker-interacting strands.[17] In biology, parts of the DNA double helix that need to separate easily, such as the TATAAT Pribnow box in some promoters, tend to have a high AT content, making the strands easier to pull apart.[18] In the laboratory, the strength of this interaction can be measured by finding the temperature required to break the hydrogen bonds, their melting temperature (also called Tm value). When all the base pairs in a DNA double helix melt, the strands separate and exist in solution as two entirely independent molecules. These single-stranded DNA molecules (ssDNA) have no single common shape, but some conformations are more stable than others.
Sense and antisense
A DNA sequence is called "sense" if its sequence is the same as that of a messenger RNA copy that is translated into protein.[20] The sequence on the opposite strand is called the "antisense" sequence. Both sense and antisense sequences can exist on different parts of the same strand of DNA (i.e. both strands contain both sense and antisense sequences). In both prokaryotes and eukaryotes, antisense RNA sequences are produced, but the functions of these RNAs are not entirely clear.[21] One proposal is that antisense RNAs are involved in regulating gene expression through RNA-RNA base pairing.

A few DNA sequences in prokaryotes and eukaryotes, and more in plasmids and viruses, blur the distinction between sense and antisense strands by having overlapping genes.[23] In these cases, some DNA sequences do double duty, encoding one protein when read along one strand, and a second protein when read in the opposite direction along the other strand. In bacteria, this overlap may be involved in the regulation of gene transcription,[24] while in viruses, overlapping genes increase the amount of information that can be encoded within the small viral genome.
Supercoiling
DNA can be twisted like a rope in a process called DNA supercoiling. With DNA in its "relaxed" state, a strand usually circles the axis of the double helix once every 10.4 base pairs, but if the DNA is twisted the strands become more tightly or more loosely wound.[26] If the DNA is twisted in the direction of the helix, this is positive supercoiling, and the bases are held more tightly together. If they are twisted in the opposite direction, this is negative supercoiling, and the bases come apart more easily. In nature, most DNA has slight negative supercoiling that is introduced by enzymes called topoisomerases.[27] These enzymes are also needed to relieve the twisting stresses introduced into DNA strands during processes such as transcription and DNA replication.
Alternate DNA structures
DNA exists in many possible conformations that include A-DNA, B-DNA, and Z-DNA forms, although, only B-DNA and Z-DNA have been directly observed in functional organisms.[10] The conformation that DNA adopts depends on the hydration level, DNA sequence, the amount and direction of supercoiling, chemical modifications of the bases, the type and concentration of metal ions, as well as the presence of polyamines in solution.[29]

The first published reports of A-DNA X-ray diffraction patterns— and also B-DNA used analyses based on Patterson transforms that provided only a limited amount of structural information for oriented fibers of DNA.[30][31] An alternate analysis was then proposed by Wilkins et al., in 1953, for the in vivo B-DNA X-ray diffraction/scattering patterns of highly hydrated DNA fibers in terms of squares of Bessel functions.[32] In the same journal, James D. Watson and Francis Crick presented their molecular modeling analysis of the DNA X-ray diffraction patterns to suggest that the structure was a double-helix.[7]

Although the `B-DNA form' is most common under the conditions found in cells,[33] it is not a well-defined conformation but a family of related DNA conformations[34] that occur at the high hydration levels present in living cells. Their corresponding X-ray diffraction and scattering patterns are characteristic of molecular paracrystals with a significant degree of disorder.[35][36]

Compared to B-DNA, the A-DNA form is a wider right-handed spiral, with a shallow, wide minor groove and a narrower, deeper major groove. The A form occurs under non-physiological conditions in partially dehydrated samples of DNA, while in the cell it may be produced in hybrid pairings of DNA and RNA strands, as well as in enzyme-DNA complexes.[37][38] Segments of DNA where the bases have been chemically modified by methylation may undergo a larger change in conformation and adopt the Z form. Here, the strands turn about the helical axis in a left-handed spiral, the opposite of the more common B form.[39] These unusual structures can be recognized by specific Z-DNA binding proteins and may be involved in the regulation of transcription