Cellular and Molecular Biology Topics
DNA and RNA are linear polymers of nucleotides. In RNA, the pentose is always ribose, in DNA is always deoxyribose. Nucleotides are linked to each other by phosphodiester bonds. When nucleotides polymerize, the hydroxyl group attached to the 3' carbon of the sugar of one nucleotide bonds to the phosphate of another.
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The phosphate is attached to the 5' carbon of the next sugar. Therefore the chain has a 5' to 3' orientation, since synthesis proceeds in that direction. The 3' end of the molecule has a free hydroxyl group, and the 5' end has a free phosphate group.
Each molecule of DNA has two strands running in opposite direction (antiparallel), held together by hydrogen bonding between the bases. RNA is usually single stranded, or forms a hyrid DNA/RNA helix. The bases for DNA are adenine, guanine, cytosine and thymine. The bases for RNA are the same except thymine is substituted by uracil.
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Ribonucleotides have a hydroxyl group at the 2' position of ribose, which is not present in deoxyribonucleotides. RNAhydrolyzes very rapidly in alkaline environment due to that hydroxyl.. The result is a mixture of 2' ribonucleotide monophosphate and 3' ribonucleotide monophosphate.
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