National Geographic : 1976 Sep
4When a cell prepares tc manufacture a protein, segment of its DA-agn The language of life .b..n.toen floating nucleotides attack to one strand of the gene AN INTRICATE molecular code spells out the genetic These nucleotides re instructions DNA carries within its double helix. aa ds isthose of DNA, but they hav replicated, or made into identarent bac Shown here are two mechanisms DNA uses. One enables copies, one for each resulting cell and uracil, r base ,e A sectionnofutheiNAstrands(left)' DNA to make a copy of itself before a cell divides. A section of the DNA strand (left places base T. As the nucleo unwinds and separates along it tides are joinedi( snl Through the other it directs the manufacture of a cell's base joints. The A's, T's, C inas, and i proteins--the vital molecules such as enzymes and G's,.now single, quickly acquired heRNAthe hormones that carry out the business of being alive. new partners from the many sis moves wavlike donC Actually components of DNA are joined chemically-; nucleotides floating free within gene to complete the pro they are here depicted as interlocking color-coded e el ventil DneA cess The long ribbon o units similar to a child's construction set. molecules form. messenger RNA, having be c~oded by the sequence o DNA bases alon hegn DNA units called nucleotides, thus relays inthgn left, each carry one of fourotein building different bases anchored to a sugar-phosphate backbone. These bases adenine, cytosine, guanine, and thymine, or A, C, G, and T-bond the nucleotides in the spiral DNA molecule, a section of which is shown Gi Below. The shapes of the bases demonstrate that A can pair up only with T, and C only with G. 2 The sequence of A's, T's, C's, and G's along the lengthy DNA ribbon contains incode the specific information that a cell needs to manufacture its particular set of proteins. By varying the sequence nature varies the instructions.