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Essential Elements

24 25 dna the elements of life Deoxyribonucleic acid, DNA to its friends, is the incredible long chain molecule at the heart of our cells which stores the genetic instructions that code for the myriad bits of our bodies. Twisted into a double helix, DNA consists of two chains of alternating sugar and phosphate molecules. Stretched between the sugars are pairs of bases opposite below joined by hydrogen bonds below. Being fussy, adenine A only bonds to thymine T, and cytosine C only to guanine G, making the two strands exact complementary opposites of each other. When our cells divide, a precise copy has to be made of our twentythree pairs of chromosomes, each a DNA molecule of some 250 million base pairs. Replication begins with the helix unwinding, which allows two new strands to form on the exposed bases. These then curl into two separate molecules, each with one old strand and one new main picture opposite. To read genetic plans, the DNA undoes a few turns, allowing messenger RNA, ribonucleic acid, a close relative of DNA which uses uracil U instead of thymime, to copy bases by hydrogen bonding. Itself uncoiling, the mRNA then carries the code to molecular factories elsewhere in the cell to make the required part, whether bone or paw, petal or claw.
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