Defining the Genetic Code
The genetic code is the set of rules by which information encoded in genetic material (DNA or mRNA sequences) is translated into proteins by living cells. This code specifies the correspondence between sequences of three nucleotides, called codons, and specific amino acids, which are the building blocks of proteins.
Key Principles and Components
Each codon consists of three consecutive nucleotide bases (e.g., A, U, G, C in mRNA). There are 64 possible codons, but only 20 common amino acids. This redundancy means multiple codons can specify the same amino acid, a property known as degeneracy. The code also includes start codons (usually AUG, coding for methionine) that initiate protein synthesis, and stop codons (UAA, UAG, UGA) that signal its termination.
A Practical Example of Translation
For instance, the mRNA sequence 'AUG-UGC-GGA-UAA' would be read as three-nucleotide codons. AUG signals the start of translation and codes for the amino acid Methionine. UGC codes for Cysteine, and GGA codes for Glycine. The UAA codon is a stop signal, indicating the end of the protein chain, at which point the ribosome disassembles, releasing the newly formed protein.
Importance in Biological Systems
The genetic code is universal, meaning it is largely the same across almost all organisms, from bacteria to humans, highlighting its fundamental role in life. Understanding the genetic code is crucial for comprehending how genetic information flows from genes to functional proteins, influencing everything from cell structure to metabolism. It is also vital for genetic engineering, diagnostics, and understanding hereditary diseases caused by mutations.