Genetic code
Groups of three bases on mRNA (codons) specify an amino acid. 64 codons cover 20 amino acids, plus start (AUG) and stop signals. The code is redundant: several codons can code for the same amino acid.
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Analogy
A dictionary where each three-letter word means one building block.
Example
mRNA: AUG GCU UAAMet - Ala - STOP
In practice
AUG means methionine and start. UAA, UAG and UGA mean stop.
Practice
Flashcards
- What is a codon?A group of three mRNA bases that codes for one amino acid or a stop signal.
Interview questions
- Compare silent, missense and nonsense mutations and say which is likely to be most harmful.
- Silent: same amino acid
- Missense: different amino acid
- Nonsense: premature stop
- Nonsense usually most damaging
Questions people ask
Why is the genetic code called redundant?
With 64 codons but only 20 amino acids, most amino acids have more than one codon. For example, leucine has six. This is useful because many mutations, particularly in the third base of a codon, change nothing in the protein. It protects cells from some damage.
Is the genetic code the same in all organisms?
Nearly. Bacteria, plants and humans read the same codons as the same amino acids, which is strong evidence of shared ancestry and what makes genetic engineering possible. A few small variants exist, for example in mitochondria and some single-celled organisms.