The first amino acid inserted into a new polypeptide chain in eukaryotic cells is usually __________.

• A. glycine
• B. serine
• C. alanine
• D. methionine

Answer: (D)

Verified step by step guidance

1. Understand that protein synthesis in eukaryotic cells begins with the process of translation, where mRNA is decoded to build a polypeptide chain.
2. Recognize that the start codon for translation in eukaryotic cells is AUG, which codes for the amino acid methionine.
3. Recall that the ribosome binds to the mRNA and identifies the start codon AUG to initiate the translation process.
4. Note that the initiator tRNA, which carries methionine, pairs with the start codon AUG on the mRNA, marking the beginning of the polypeptide chain.
5. Conclude that methionine is the first amino acid incorporated into the new polypeptide chain during protein synthesis in eukaryotic cells.