Biology AS · Nucleic acids and protein synthesis. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
A nucleotide has three parts: a pentose sugar, a phosphate group and a nitrogenous base. DNA nucleotides contain deoxyribose and the bases A, T, C and G. RNA nucleotides contain ribose and have uracil in place of thymine. ATP is also a nucleotide: adenine, ribose and three phosphate groups.
DNA is a double helix of two polynucleotide strands. In each strand the nucleotides are joined by phosphodiester bonds. The two strands run in opposite directions (antiparallel) and are held together by hydrogen bonds between complementary bases.
In semi-conservative replication the strands separate and each one is a template, so every new molecule has one old strand and one new strand. mRNA is a single, unpaired strand.
Using %A = %T for a single strand or for RNA. The pairing rule gives equal amounts only in a double-stranded molecule, so check for uracil and unequal percentages first.
Answer: 110 thymine bases.
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