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DNA and the genome
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DNA holds the instructions for building every protein in your body. Its structure explains how it can be copied so accurately.
The double helix
DNA is a polymer made of two strands twisted into a double helix.
Each unit is a nucleotide: a sugar, a phosphate group and one of four bases.
Each unit is a nucleotide: a sugar, a phosphate group and one of four bases.
Complementary base pairs
The bases pair up across the two strands:
A pairs with T, C pairs with G.
The pairs are held together by weak hydrogen bonds.
A pairs with T, C pairs with G.
The pairs are held together by weak hydrogen bonds.
Genes and the genome
A gene is a section of DNA that codes for a specific protein.
The genome is all the genetic material of an organism.
DNA is found in chromosomes in the nucleus.
The genome is all the genetic material of an organism.
DNA is found in chromosomes in the nucleus.
In a DNA sample, 20% of the bases are A. What percentage are C?
- A pairs with T, so T is also 20%.
- A + T = 40%, so C + G = 60%.
- C pairs with G, so they are equal: 60 ÷ 2 = 30%.
Answer: 30%
DNA is a double helix of nucleotides. A pairs with T and C pairs with G. A gene codes for one protein; the genome is all of an organism's DNA.
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