Word: celling
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Dates: during 1980-1989
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...concern, as well as the cost, reflects the complexity of the human genome and the magnitude of the effort required to understand it. DNA is found in the human-cell nucleus in the form of 46 separate threads, each coiled into a packet called a chromosome. Unraveled and tied together, these threads would form a fragile string more than 5 ft. long but only 50 trillionths of an inch across...
Fundamental to the genius of DNA is the fact that A and T are mutually attractive, as are C and G. Consequently, when DNA separates during cell division, coming apart at the middle of each rung like a zipper opening, an exposed T half-rung on one side of the ladder will always attract an A floating freely in the cell. The corresponding A half-rung on the other section of the ladder will attract a floating T, and so on, until two double helixes, each identical to the original DNA molecule, are formed...
Even more remarkable, each of the four bases represents a letter in the genetic code. The three-letter "words" they spell, reading in sequence along either side of the ladder, are instructions to the cell on how to assemble amino acids into the proteins essential to the structure and life of its host. Each complete DNA "sentence" is a gene, a discrete segment of the DNA string responsible for ordering the production of a specific protein...
Reading these genetic words and deciphering their meaning is apparently a snap for the clever machinery of a cell. But for mere scientists it is a formidable and time-consuming task. For instance, a snippet of DNA might read ACGGTAGAT, a message that researchers can decipher rather easily. It codes for a sequence of three of the 20 varieties of amino acids that constitute the building blocks of proteins. But the entire genome of even the simplest organism dwarfs that snippet. The genetic blueprint of the lowly E. coli bacterium, for one, is more than 4.5 million base pairs long...
...fact, some of the nongene regions on the genome have already been identified as instructions necessary for DNA to replicate itself during cell division. Their message is obviously detailed and complex. Explains George Bell, head of genome studies at Los Alamos National Laboratory: "It's as if you had a rope that was maybe 2 in. in diameter and 32,000 miles long, all neatly arranged inside a structure the size of a superdome. When the appropriate signal comes, you have to unwind the rope, which consists of two strands, and copy each strand so you end up with...