Q.State a functional difference between the following codons :

Here is the functional difference between the given codons and properties:

• (a) AUG and UAA:
  • AUG is a start codon that codes for the amino acid methionine and initiates the process of translation (protein synthesis).
  • UAA is a stop codon (or nonsense codon) that does not code for any amino acid and signals the termination of translation.
• (b) Specific and Degenerate:
  • The genetic code is specific because a particular codon codes for only one specific amino acid. …

The genetic code, fundamental to all life, is a set of rules by which information encoded in genetic material (DNA or RNA) is translated into proteins. This information is carried in sequences of three nucleotides, called codons, on messenger RNA (mRNA). Each codon typically specifies a particular amino acid or signals the start or end of protein synthesis. Understanding the functional differences between various types of codons is crucial for grasping how proteins are accurately made.

(a) Functional difference between AUG and UAA

The codons AUG and UAA play distinct and critical roles in the process of protein synthesis, known as translation.

• AUG (Methionine Codon / Start Codon):

  • Initiation: AUG serves as the primary start codon for protein synthesis. When the ribosome encounters an AUG codon on the mRNA, it signals the beginning of the translation process, ensuring that the protein synthesis machinery starts at the correct point.
  • Amino Acid Specification: Beyond its role in initiation, AUG also codes for the amino acid methionine (Met). Therefore, the first amino acid incorporated into a newly synthesized polypeptide chain is typically methionine, directed by this codon.

• UAA (Stop Codon):

  • Termination: UAA functions as a stop codon (also known as a nonsense codon). Unlike AUG, it does not code for any amino acid. When the ribosome reaches a UAA codon on the mRNA, it signals the termination of protein synthesis.
  • Release: Instead of recruiting an amino acid, UAA (along with other stop codons like UAG and UGA) recruits specific release factors. These factors cause the ribosome to dissociate from the mRNA and release the completed polypeptide chain, effectively ending the protein synthesis process.

(b) Functional difference between Specific and Degenerate codons

The terms "specific" and "degenerate" describe two important characteristics of the genetic code, highlighting how codons relate to the amino acids they specify.

• Specific (or Unambiguous) Codons:

  • Unique Assignment: The genetic code is considered specific or unambiguous because one codon codes for only one specific amino acid. For instance, the codon UUU always codes for Phenylalanine and never for any other amino acid. Similarly, GGU always codes for Glycine.
  • Accuracy: This specificity ensures that there is no ambiguity in the translation process. Each codon has a unique meaning, which is vital for maintaining the precise sequence of amino acids in a protein, thereby preserving its correct structure and function.

• Degenerate Codons: …