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Biology
Francis Crick: Co-Discoverer of the DNA Double Helix
DNA structure, the Central Dogma, and the genetic code
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Francis Crick was a British scientist who helped reveal one of biology's most important ideas: the structure of DNA. In 1953, Crick and James Watson proposed the double helix model, using evidence from Rosalind Franklin, Maurice Wilkins, and others. This model explained how genetic information can be stored, copied, and passed from one generation to the next. Crick's work helped turn biology into a molecular science based on atoms, bonds, and information.
Key Facts
- Francis Crick lived from 1916 to 2004 and was a co-discoverer of the DNA double helix.
- The DNA double helix model was published by Watson and Crick in 1953.
- DNA base pairing follows A pairs with T and C pairs with G.
- Chargaff's rule for double-stranded DNA: %A = %T and %C = %G.
- Central Dogma: DNA -> RNA -> protein.
- A codon is a sequence of 3 RNA bases, so 1 codon codes for 1 amino acid or a stop signal.
Vocabulary
- DNA
- DNA is the molecule that stores genetic instructions in cells using a sequence of nucleotide bases.
- Double helix
- A double helix is the twisted ladder shape of DNA made from two strands running in opposite directions.
- Base pair
- A base pair is a matched pair of DNA bases held together by hydrogen bonds, such as A with T or C with G.
- Central Dogma
- The Central Dogma describes the usual flow of genetic information from DNA to RNA to protein.
- Genetic code
- The genetic code is the set of rules that connects RNA codons with specific amino acids or stop signals.
Common Mistakes to Avoid
- Saying Crick discovered DNA itself is wrong because DNA was identified in the 1800s, while Crick helped determine its structure in 1953.
- Forgetting Rosalind Franklin's evidence is wrong because her X-ray diffraction images were crucial for understanding DNA's helical shape.
- Pairing A with C or G with T is wrong because DNA base pairing is specific: A pairs with T and C pairs with G.
- Treating the Central Dogma as a chemical reaction is wrong because it is a model for information flow, not a single step in metabolism.
Practice Questions
- 1 A double-stranded DNA sample contains 30% adenine. What percentages of thymine, cytosine, and guanine does it contain?
- 2 A messenger RNA has 90 bases in its coding region, not counting the stop codon. How many amino acids are encoded?
- 3 Explain how the double helix structure helps DNA copy itself accurately during cell division.