GCSE Biology · Edexcel 1BI0 · Topic 3C
DNA and protein synthesis
Key points
- DNA is a polymer made of two strands twisted into a double helix. Each unit is a nucleotide: a sugar, a phosphate and one of four bases (A, T, C, G).
- Complementary base pairing: A pairs with T, C pairs with G, joined by weak hydrogen bonds.
- A gene is a section of DNA that codes for one protein. The genome is all the DNA of an organism.
- Practical: DNA can be extracted from fruit using detergent, salt and cold ethanol.
- Transcription (in the nucleus): RNA polymerase makes mRNA from the DNA of a gene. Translation (at a ribosome): each three-base codon is matched by tRNA, which brings a specific amino acid; the amino acids join to form a protein.
- Higher tier: a mutation in the non-coding DNA before a gene can affect how much RNA polymerase binds, changing how much protein is made.
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DNA carries the instructions to build every protein in an organism. This sub-topic covers DNA's structure, how to extract it and, in detail, how cells read a gene to make a protein.
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