What is the start codon and its role?

What is the start codon and its role?

• A. UAA; signals termination
• B. GGU; codes for glycine
• C. AUG; codes for methionine and signals start of translation
• D. UCU; codes for serine

Answer: (C)

The start codon is AUG, and it has two important roles: it specifies where the ribosome begins translating the mRNA and it encodes the amino acid methionine. When the ribosome recognizes AUG, initiator tRNA carrying methionine pairs with it, assembling the initiation complex and establishing the reading frame for all downstream codons. In bacteria, the initiator carries a formyl group (formyl-methionine) but the AUG signal remains the start cue. From there, synthesis proceeds with methionine at the N-terminus (often removed later) and elongation follows codon-by-codon. The other options don’t fit because UAA is a stop codon that ends translation, not a start signal; GGU codes for glycine; UCU codes for serine.

The start codon is AUG, and it has two important roles: it specifies where the ribosome begins translating the mRNA and it encodes the amino acid methionine. When the ribosome recognizes AUG, initiator tRNA carrying methionine pairs with it, assembling the initiation complex and establishing the reading frame for all downstream codons. In bacteria, the initiator carries a formyl group (formyl-methionine) but the AUG signal remains the start cue. From there, synthesis proceeds with methionine at the N-terminus (often removed later) and elongation follows codon-by-codon.

The other options don’t fit because UAA is a stop codon that ends translation, not a start signal; GGU codes for glycine; UCU codes for serine.