Question

Discuss the nature of genetic code.

Hint:

Mnemonic for Stop Codons:
{U} {A}re {A}way (UAA)
{U} {A}re {G}one (UAG)
{U} {G}o {A}way (UGA)

Answer 1

Step 1: Understanding the Concept:
The genetic code is the "dictionary" used by the ribosome during translation.
Since there are 4 nucleotides and 20 amino acids, a single (4) or doublet (16) code is insufficient; a triplet code ($4^{3} = 64$) provides more than enough combinations.
Step 2: Detailed Explanation:
The "nature" of the code is defined by several unique properties:
1. The Triplet Codon: Each "word" in mRNA is a sequence of three bases. Of the 64 codons, 61 code for amino acids.
2. Unambiguous: A specific codon always codes for the same amino acid (e.g., GUG always codes for Valine). There is no confusion.
3. Degenerate: Many amino acids are coded by more than one codon (e.g., Serine is coded by 6 different codons). This provides a buffer against mutations.
4. Comma-less: The code is read sequentially without any gaps or overlapping of bases. If one base is deleted, the entire "reading frame" shifts.
5. Universal: The code is nearly identical across all life forms, from a simple E. coli to a complex Human. This is strong evidence for a common ancestor.
6. Start and Stop Signals:
- AUG is the start codon (it also codes for Methionine).
- UAA, UAG, UGA are stop codons (nonsense codons) that do not code for any amino acid and signal the end of translation.
Step 3: Final Answer:
The genetic code is a highly organized, universal system that ensures the accurate translation of genetic information into functional proteins.