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Unformatted text preview: Figure 8 shows how two strands of nucleotides, paired by weak hydrogen bonds between the bases, form a double-stranded DNA. When bonded in this way, DNA forms a two-stranded spiral, or double helix. Note that adenine always bonds with thymine and cytosine always bonds with guanine. RNA differs from DNA in the following ways: The sugar in the nucleotides that make an RNA molecule is ribose, not deoxyribose as it is in DNA. The thymine nucleotide does not occur in RNA. It is replaced by uracil. When pairing of bases occurs in RNA, uracil (instead of thymine) pairs with adenine. RNA is usually single-stranded and does not form a double helix as does DNA....
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- Spring '10