Question

The start codon for protein synthesis is

• A. UAA
• B. UGA
• C. UAG
• D. AUG

Hint:

Remember the genetic code: \[ \boxed{\text{Start Codon} = AUG} \] \[ \boxed{\text{Stop Codons} = UAA,\ UAG,\ UGA} \] AUG always establishes the reading frame during translation.

Answer 1

The Correct Option is D

Concept: Protein synthesis begins with the process of translation, where the ribosome reads the mRNA sequence in groups of three nucleotides called codons. The first codon recognized by the ribosome is known as the start codon. In almost all organisms, the universal start codon is AUG, which codes for the amino acid methionine (or formyl methionine in prokaryotes).

Step 1: Understand the role of the start codon.
The start codon signals the ribosome where protein synthesis should begin. It determines the correct reading frame for translation. \[ \boxed{\text{mRNA} \longrightarrow \text{AUG} \longrightarrow \text{Translation Begins}} \]

Step 2: Role of AUG.
The codon AUG:
• Initiates protein synthesis.
• Codes for Methionine (Met) in eukaryotes.
• Codes for N-formyl methionine (fMet) in prokaryotes. Every newly synthesized protein begins with this codon unless special exceptions occur.

Step 3: Eliminate the incorrect options.

• UAA, UAG and UGA are stop codons.
• They terminate protein synthesis rather than initiate it.
• AUG is the universal initiation codon. Final Answer: \[ \boxed{Option (D) is correct \]