Steriods

IUPAC-recommended ring-lettering (left) and atom-numbering
(right) ofcholestane, a prototypical steroid skeleton.
The four rings A-D form the gonanenucleus of the steroid.

A steroid is a type of organic compound that contains a characteristic arrangement of four cycloalkane rings that are joined to each other. Examples of steroids include the dietary fat cholesterol, the sex hormones estradiol and testosterone, and the anti-inflammatory drug dexamethasone. The core of steroids is composed of twenty carbon atoms bonded together that take the form of four fused rings: three cyclohexane rings (designated as rings A, B, and C in the figure to the right) and one cyclopentane ring (the D ring). The steroids vary by the functional groups attached to this four-ring core and by the oxidation state of the rings. Sterols are special forms of steroids, with a hydroxyl group at position-3 and a skeleton derived from cholestane.

Hundreds of distinct steroids are found in plants, animals, and fungi. All steroids are made in cells either from the sterols lanosterol (animals and fungi) or from cycloartenol(plants). Both lanosterol and cycloartenol are derived from the cyclization of the triterpene squalene.

Stick model of the steroid lanosterol. The total number of carbons (30) reflects its triterpenoid origin.

Structure:
Steroids are a class of organic compounds with a chemical structure that contains the core of gonane or a skeleton derived therefrom. Usually, methyl groups are present at the carbons C-10 and C-13 – an alkyl side-chain at carbon C-17 may also be present.

Cholesterol. This steroid is the precursor to other steroidsin the steroidogenesis.

The basic skeleton of a steroid, with standard stereo orientation. R is a side-chain at C-17.

Steroids are a class of organic compounds with a chemical structure that contains the core of gonane or a skeleton derived therefrom. Usually, methyl groups are present at the carbons C-10 and C-13 – an alkyl side-chain at carbon C-17 may also be present.

Gonane is the simplest possible steroid and is composed of seventeen carbon atoms, bonded together to form four fused rings. The three cyclohexane rings (designated as rings A, B, and C in the figure below) form the skeleton of phenanthrene; ring D has acyclopentane structure. Hence, together they are called cyclopentaphenanthrene.

Commonly, steroids have a methyl group at the carbons C-10 and C-13 and an alkyl side chain at carbon C-17. Further, they vary by the configuration of the side chain, the number of additional methyl groups, and the functional groups attached to the rings. For example, sterols have a hydroxyl group attached at position C-3.

Some exemplary steroids with their structures:

Classification:

Taxonomical/Functional

Some of the common categories of steroids:

• Animal
  • Insect
    • Ecdysteroids such as ecdysterone
  • Vertebrate
    • Steroid hormones
      • Sex steroids are a subset of sex hormones that produce sex differences or support reproduction. They include androgens,estrogens, and progestagens.
      • Corticosteroids include glucocorticoids and mineralocorticoids. Glucocorticoids regulate many aspects of metabolism andimmune function, whereas mineralocorticoids help maintain blood volume and control renal excretion of electrolytes. Most medical 'steroid' drugs are corticosteroids.
      • Anabolic steroids are a class of steroids that interact with androgen receptors to increase muscle and bone synthesis. There are natural and synthetic anabolic steroids. In popular language, the word "steroids" usually refers to anabolic steroids.
    • Cholesterol, which modulates the fluidity of cell membranes and is the principal constituent of the plaques implicated in atherosclerosis.
• Plant
  • Phytosterols
  • Brassinosteroids
• Fungus
  • Ergosterols

Structural

It is also possible to classify steroids based upon their chemical composition. One example of how MeSH performs this classification is available at the Wikipedia MeSH catalog. Examples from this classification include:

Class	Examples	Number of carbon atoms
Cholestanes	cholesterol	27
Cholanes	cholic acid	24
Pregnanes	progesterone	21
Androstanes	testosterone	19
Estranes	estradiol	18

Gonane (or steroid nucleus) is the parent (17-carbon tetracyclic) hydrocarbon molecule without any alkyl sidechains.

Source: Wikipedia

The Bermuda Triangle

The Bermuda Triangle, also known as the Devil's Triangle, is a region in the western part of the North Atlantic Ocean where a number of aircraft and surface vessels are said to have disappeared under mysterious circumstances. Popular culture has attributed these disappearances to the paranormal or activity by extraterrestrial beings. Documented evidence indicates that a significant percentage of the incidents were spurious, inaccurately reported or embellished by later authors.

You may watch the documentary which is on the left of this. It's a great resource for the devil's triangle.

 The boundaries of the triangle cover the Straits of Florida, the Bahamas and the Atlantic east to the Azores. The more familiar triangular boundary in most written works has as its points somewhere on the Atlantic coast of Miami; San Juan, Puerto Rico; and the mid-Atlantic island of Bermuda, with most of the accidents concentrated along the southern boundary around the Bahamas and the Florida Straits.

The area is one of the most heavily traveled shipping lanes in the world, with ships crossing through it daily for ports in the Americas, Europe, and the Caribbean Islands. Cruise ships are also plentiful, and pleasure craft regularly go back and forth between Florida and the islands. It is also a heavily flown route for commercial and private aircraft heading towards Florida, the Caribbean, and South America from points north.

The earliest allegation of unusual disappearances in the Bermuda area appeared in a September 16, 1950 Associated Press article by Edward Van Winkle Jones. Two years later, Fate magazine published "Sea Mystery at Our Back Door", a short article by George X. Sand covering the loss of several planes and ships, including the loss of Flight 19, a group of five U.S. Navy TBM Avenger bombers on a training mission. Sand's article was the first to lay out the now-familiar triangular area where the losses took place. Flight 19 alone would be covered in the April 1962 issue of American Legion Magazine. It was claimed that the flight leader had been heard saying "We are entering white water, nothing seems right. We don't know where we are, the water is green, no white." It was also claimed that officials at the Navy board of inquiry stated that the planes "flew off to Mars." Sand's article was the first to suggest a supernatural element to the Flight 19 incident. In the February 1964 issue of Argosy, Vincent Gaddis's article "The Deadly Bermuda Triangle" argued that Flight 19 and other disappearances were part of a pattern of strange events in the region. The next year, Gaddis expanded this article into a book, Invisible Horizons.

Others would follow with their own works, elaborating on Gaddis's ideas: John Wallace Spencer (Limbo of the Lost, 1969, repr. 1973); Charles Berlitz (The Bermuda Triangle, 1974); Richard Winer (The Devil's Triangle, 1974), and many others, all keeping to some of the same supernatural elements outlined by Eckert.

Source: Wikipedia The Free Encyclopedia

The Atlantis

Atlantis—True Story or Cautionary Tale

An illustration by Sir Gerald Hargreaves shows a utopian scene on a cove of the mythical land of Atlantis. Many scholars think Plato invented the story of Atlantis as a way to present his philosophical theories.

Photograph by Mary Evans Picture Library/Everett Collection

By Willie Drye

If the writing of the ancient Greek philosopher Plato had not contained so much truth about the human condition, his name would have been forgotten centuries ago.But one of his most famous stories—the cataclysmic destruction of the ancient civilization of Atlantis—is almost certainly false. So why is this story still repeated more than 2,300 years after Plato's death?"It's a story that captures the imagination," says James Romm, a professor of classics at Bard College in Annandale, New York. "It's a great myth. It has a lot of elements that people love to fantasize about."Plato told the story of Atlantis around 360 B.C. The founders of Atlantis, he said, were half god and half human. They created a utopian civilization and became a great naval power. Their home was made up of concentric islands separated by wide moats and linked by a canal that penetrated to the center. The lush islands contained gold, silver, and other precious metals and supported an abundance of rare, exotic wildlife. There was a great capital city on the central island.There are many theories about where Atlantis was—in the Mediterranean, off the coast of Spain, even under what is now Antarctica. "Pick a spot on the map, and someone has said that Atlantis was there," says Charles Orser, curator of history at the New York State Museum in Albany. "Every place you can imagine."Plato said Atlantis existed about 9,000 years before his own time, and that its story had been passed down by poets, priests, and others. But Plato's writings about Atlantis are the only known records of its existence.

Possibly Based on Real Events?

Few, if any, scientists think Atlantis actually existed. Ocean explorer Robert Ballard, the National Geographic explorer-in-residence who discovered the wreck of the Titanic in 1985, notes that "no Nobel laureates" have said that what Plato wrote about Atlantis is true.

Still, Ballard says, the legend of Atlantis is a "logical" one since cataclysmic floods and volcanic explosions have happened throughout history, including one event that had some similarities to the story of the destruction of Atlantis. About 3,600 years ago, a massive volcanic eruption devastated the island of Santorini in the Aegean Sea near Greece. At the time, a highly advanced society of Minoans lived on Santorini. The Minoan civilization disappeared suddenly at about the same time as the volcanic eruption.

But Ballard doesn't think Santorini was Atlantis, because the time of the eruption on that island doesn't coincide with when Plato said Atlantis was destroyed.

Romm believes Plato created the story of Atlantis to convey some of his philosophical theories. "He was dealing with a number of issues, themes that run throughout his work," he says. "His ideas about divine versus human nature, ideal societies, the gradual corruption of human society—these ideas are all found in many of his works. Atlantis was a different vehicle to get at some of his favorite themes."

The legend of Atlantis is a story about a moral, spiritual people who lived in a highly advanced, utopian civilization. But they became greedy, petty, and "morally bankrupt," and the gods "became angry because the people had lost their way and turned to immoral pursuits," Orser says.

As punishment, he says, the gods sent "one terrible night of fire and earthquakes" that caused Atlantis to sink into the sea.