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Complementary base pairing
These complementary base pairs are the only ways the bases can bond and join the two nucleotide chains. Thus, the sequence of bases along one polynudeotide chain determines the sequence along the other: an adenine on one chain means there must be a thymine on the other chain at that point, and so on. Complementary base pairing forms the basis of DNA replication and its ability to form messenger RNA during protein synthesis. Complementary base pairing can happen only if the two polynudeotide chains are antiparallel. Antiparallel chains run in opposite directions; one chain runs from 3' to 5', and the other from 5' to 3'. Watson and Crick's model of DNA showed that the base pairs are 0.34 nm apart, and that each complete turn of the helix has ten base pairs. In summary DNA is a double helix made of two polynucleotide chains. Each chain has a sugar-phosphate backbone on the outside with organic bases on the inside. The two chains are held together by complementary base pairing. The chains are antiparallel (the 5' end of one chain lies next to the 3' end of the other chain). Glossary of essential terms for you to know
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