GCSE Biology Revision — DNA & Genetics
Revise DNA & Genetics for GCSE Biology with a topic explanation, worked example and common mistakes. Check the board notes for specification differences.
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What is DNA & Genetics?
DNA (deoxyribonucleic acid) is the molecule that carries the genetic instructions for the development, functioning, growth and reproduction of all known organisms and many viruses. It is a double helix structure, made of two strands of nucleotides. A gene is a short section of DNA that codes for a specific protein.
Board notes: A fundamental topic for all major boards (AQA, Edexcel, OCR). The structure of DNA and the concept of the genome are key.
Step-by-step explanationWorked examples
Worked example
A short section of one DNA strand has the base sequence A-T-T-C-G. The complementary strand that pairs with it would have the sequence T-A-A-G-C. This complementary base pairing is fundamental to DNA's structure and replication.
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Common mistakes
- 1Confusing DNA, genes, and chromosomes. DNA is the molecule itself. A gene is a segment of DNA that codes for a protein. A chromosome is a long, coiled structure made of DNA and proteins found in the nucleus.
- 2Thinking that DNA is only in the nucleus. In eukaryotes, most DNA is in the nucleus, but mitochondria also contain their own small loop of DNA.
- 3Forgetting the four bases. The four nucleotide bases in DNA are Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). Remember A always pairs with T, and C always pairs with G.
DNA & Genetics exam questions
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Frequently asked questions
What is the structure of DNA?
DNA has a double helix structure, often described as a twisted ladder. The two sides of the ladder are made of alternating sugar and phosphate groups, and the rungs are made of pairs of nitrogenous bases (A with T, C with G).
What is the genome?
The genome is the entire set of genetic material in an organism. The Human Genome Project was a major international research effort to map the entire human genome.