A codon sequence of three nucleotides (triplet) in messenger RNA (mRNA) that specifies a single amino acid to be added during protein synthesisstart or stop of translation. Codons are the fundamental units of the genetic code .
Key Features:
Each codon consists of three RNA bases (A, U, C, G).
The genetic code is read in triplets , with no overlap .
Codons are read by ribosomes translation .
There are 64 possible codons (4³ combinations of A, U, C, G).
Types of Codons: Type Description Sense codons Code for the 20 standard amino acids (61 codons) Start codon Begins translation; AUG codes for methionine Stop codons Signal the end of translation: UAA, UAG, UGA (do not code for amino acids)
Examples of Codons and Their Amino Acids: Codon Amino Acid AUG Methionine (Start) UUU Phenylalanine GGC Glycine UAA Stop CGA Arginine
Important Properties of the Genetic Code: Property Description Universal Nearly all organisms use the same codon-to-amino acid assignments Redundant Multiple codons can code for the same amino acid (e.g., Leucine has 6 codons) Unambiguous Each codon specifies only one amino acid Non-overlapping Codons are read one after another in sets of three
Codons vs. Anticodons: Term Location Function Codon mRNA Encodes an amino acid Anticodon tRNA Complementary triplet that binds to codon during translation
Biological Importance:
Protein synthesis : Codons determine the sequence of amino acids in a protein.Gene expression : Start and stop codons define the open reading frame.Mutations : Codon changes can lead to:
Silent mutations (no change in amino acid)Missense mutations (changes one amino acid)Nonsense mutations (introduces a premature stop)
Summary Table: Feature Description Definition 3-nucleotide sequence in mRNA Function Specifies amino acids or signals translation start/stop Number 64 total (61 for amino acids, 3 stop codons) Start Codon AUG (methionine) Stop Codons UAA, UAG, UGA Location In mRNA, read during translation
