Biology · A Unity and diversity. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
DNA is the genetic material of all living organisms. DNA and RNA are polymers built from nucleotides. Each nucleotide has three parts: a pentose sugar, a phosphate group and a nitrogenous base.
Nucleotides join by condensation. The phosphate of one bonds to the sugar of the next, which makes a strong sugar–phosphate backbone with the bases sticking out.
DNA is a double helix of two antiparallel strands, which run in opposite directions. Hydrogen bonds between complementary base pairs hold the strands together. Because each base fits only one partner, the sequence of one strand fixes the sequence of the other, so the information can be copied exactly.
Percentages are often worked out from one strand only. The rule A = T and C = G applies to the whole double-stranded molecule, and RNA never contains thymine.
Answer: 280 thymine bases.
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