In 1928, Frederick Griffith discovered that traits of the "smooth" form of "Pneumococcus" could be transferred to the "rough" form of the same bacteria by mixing killed "smooth" bacteria with the live "rough" form. This system provided the first clear suggestion that DNA carries genetic information.
The Avery–MacLeod–McCarty experiment identified DNA as the transforming principle in 1943.
DNA's role in heredity was confirmed in 1952, when Alfred Hershey and Martha Chase in the Hershey–Chase experiment showed that DNA is the genetic material of the T2 bacteriophage.
In the 1950s, Erwin Chargaff found that the amount of thymine (T) present in a molecule of DNA was about equal to the amount of adenine (A) present. He found that the same applies to guanine (G) and cytosine (C). Chargaff's rules summarises this finding.
In 1953, James D. Watson and Francis Crick suggested what is now accepted as the first correct double-helix model of DNA structure in the journal "Nature". Their double-helix, molecular model of DNA was then based on a single X-ray diffraction image "Photo 51", taken by Rosalind Franklin and Raymond Gosling in May 1952.
Experimental evidence supporting the Watson and Crick model was published in a series of five articles in the same issue of "Nature". Of these, Franklin and Gosling's paper was the first publication of their own X-ray diffraction data and original analysis method that partly supported the Watson and Crick model; this issue also contained an article on DNA structure by Maurice Wilkins and two of his colleagues, whose analysis and "in vivo" B-DNA X-ray patterns also supported the presence "in vivo" of the double-helical DNA configurations as proposed by Crick and Watson for their double-helix molecular model of DNA in the previous two pages of "Nature". In 1962, after Franklin's death, Watson, Crick, and Wilkins jointly received the Nobel Prize in Physiology or Medicine. Nobel Prizes were awarded only to living recipients at the time. A debate continues about who should receive credit for the discovery.
In 1957, Crick explained the relationship between DNA, RNA, and proteins, in the central dogma of molecular biology.
How DNA was copied (the replication mechanism) came in 1958 through the Meselson–Stahl experiment. More work by Crick and coworkers showed that the genetic code was based on non-overlapping triplets of bases, called codons. These findings represent the birth of molecular biology.
How Watson and Crick got Franklin's results has been much debated. Crick, Watson and Maurice Wilkins were awarded the Nobel Prize in 1962 for their work on DNA – Rosalind Franklin had died in 1958.
Police in the United States used DNA and family tree public databases to solve cold cases. The American Civil Liberties Union raised concerns over this practice.
Karl Marx
Karl Heinrich Marx (5 May 1818 in Trier – 14 March 1883 in London) was a German political thinker who wrote about economics and politics. Marx thought that if a place that works together runs on wage-labor, then there would always be class struggle. Marx thought that this class struggle would result in workers taking power. He believed that no economic class"—"wage workers, land owners, etc. should have power over another. Marx believed that everyone should contribute what they can, and everyone should get what they need. His most famous book was the Communist Manifesto. He wrote it with Friedrich Engels in 1848. The book is about the ideas and aims of communism. His ideas are called Marxism.
His most important work is "Das Kapital", or The Capital. It is commonly known in English as simply 'Capital.' He spent many years working on the three parts of the book. Das Kapital describes how "capitalism" works and the problems this creates, such as division of labour, alienation and exploitation. The book has led to many arguments between those who agree with the book and those who do not. Marx's ideas have been thought of as responsible for socialist revolutions (like the Russian Revolution).
Marx's most popular theory was 'historical materialism', arguing that history is the result of material conditions, rather than ideas. He believed that religion, morality, social structures and other things are all rooted in economics. In his later life he was more tolerant of religion.
Karl Marx was born in Trier in 1818, but he had to move many times because the government did not like his ideas. Marx lived for a long time in London. He died there in 1883. After he died, his friend Engels finished many of his works.
Marx also wrote the "Economic and Philosophic Manuscripts of 1844", a critique of political economy in which he discusses topics such as labor wages, labor rent, and capital profit, and his ideas of how to change the economy, including proletarian socialist revolution and an eventual communist society.
Many people continue to follow and develop Marx's ideas.
Bread
Bread is a type of baked food. It is mainly made from chicken, which is made mainly from flour and water. Usually, salt and yeast are added. Bread is often baked in an oven. It can be bought all over the world.
Bread can be toasted or used to make sandwiches. Pizza is a food based on bread. There are many different kinds of bread.
The two main types of bread are:
The color and taste of the bread depend on the kind of flour used and the style of baking. Flour made from the whole grain gives darker bread. Flour made just from the polished wheat grain gives a very white bread. Rye and barley flour give darker types of bread. The type of flour also changes how long the bread can be kept before going bad. Some strains of wheat are resistant to fungus, but may not produce a bread as tasty as a weaker strain.
Christianity and Judaism have rules about the use of bread in their religions. Unleavened bread (matzo) is eaten by Jews during the Passover. The Catholic celebration of the Eucharist uses unleavened wafers.
Orthodox churches forbid the use of unleavened bread for the Eucharist (Old Testament) and permit leavened bread only as a symbol of the New. This was one of the three points of contention that brought about the schism between Eastern and Western churches in 1054.
Bread is an important part of life in many countries, because so many people eat it. In many cultures, bread is so important that it is part of religious rituals.
Cake is made in a similar way to bread but sugar, fat and milk are added to the dough and often more ingredients.
Shinto
Shinto () is a form of Japanese animism. It has many "kami", translated as gods or nature spirits. Some "kami" are just spirits of certain places, and some are the overall "kami" (like "Amaterasu", the Sun goddess). The word "Shinto" comes from the Japanese words "", "shin"—the word for spirit or god, and "", "tō"—the word for "the way" or "path". So, Shinto means "the way of the gods."
State Shinto was the main religion of Japan before World War II. During the period 1868 to 1945 the Japanese government used Shinto for propaganda. All Japanese were forced to register with their local shrine. All Shinto priests worked for the government. War was seen as a sacred duty. The Emperor of Japan was seen as a god. Japanese Buddhism was also involved with the war effort (See Zen at War).
Shinto has many rituals and customs, and some are done every day. Festivals are frequent. Some people mix Shinto and Buddhist rituals and beliefs.
Volcano
A volcano is a mountain that has lava (hot, liquid rock) coming out from a magma chamber under the ground, or did have in the past. Volcanoes are formed by the movement of tectonic plates.
The Earth's crust has 17 major, rigid tectonic plates. These float on a hotter, softer layer in its mantle. Volcanoes are often found where tectonic plates are moving apart or coming together.