Genetic Code
- Definition: The genetic code transfers information from nucleic acids to proteins using codons (triplets of nucleotides).
- Codons: 64 total; 61 code for amino acids, 3 are stop signals (UAA, UAG, UGA). Most amino acids have multiple codons (degeneracy), typically differing at the third position. AUG codes for methionine and serves as the start codon.
- Features:
- Codons are non-overlapping and continuous (no "commas").
- The code was deciphered using synthetic mRNA and in vitro translation.
- Universality: Mostly conserved across life, with minor variations (e.g., mitochondrial codes) that reduce tRNA requirements.
- Reading Frames: Each way to divide DNA or RNA into codons is called a reading frame. A reading frame starts with an AUG codon and ends with a stop codon. RNA has 3 possible reading frames, and DNA has 6 frames (3 for each strand).
2 Types: Closed(After each start codon, a stop codon will soon come) and Open(there will be no stop codons for a good length, because natural selection keeps them away).
- Point Mutations:
- Substitution: Can be silent (no change), missense (different amino acid), or nonsense (premature stop).
- Insertion/Deletion: Cause frameshift mutations, drastically altering downstream protein sequence.