Which of the following statements best describes protein synthesis?

Analyzing the question: We need the statement that correctly describes protein synthesis (transcription and translation).

Key concept: Protein synthesis has two stages:

1. Transcription (in the nucleus): DNA is copied into mRNA.
2. Translation (at the ribosome): mRNA is read in codons (triplets). Each tRNA has an anticodon that pairs with a matching codon and carries a specific amino acid. The ribosome then translocates (moves) along the mRNA by one codon, exposing the next codon for a new tRNA to bind.

Evaluating each option:

• A. DNA is directly involved in translation. False. DNA stays in the nucleus. mRNA, tRNA and rRNA carry out translation.
• B. Translocation of the ribosomes exposes a new codon for base pairing with an amino acid (tRNA's anticodon). True. After each peptide bond forms, the ribosome shifts along the mRNA by one codon. This exposes the next codon so that the matching tRNA, carrying its amino acid, can pair with it. (Strictly, the codon pairs with the tRNA anticodon, but this is the intended meaning.)
• C. Each tRNA with a particular anticodon always carries a different protein. False. tRNA carries an amino acid, not a protein, and each anticodon is linked to one specific amino acid.
• D. One amino acid is always carried by more than one... The option is incomplete. It likely refers to more than one tRNA. Many amino acids do have several tRNAs because the genetic code is degenerate, but "always" is wrong, since some amino acids (such as methionine and tryptophan) have only one codon. The statement is also cut off.

Exam tip: Remember the order "Transcription → Translation → Translocation". In translation, the ribosome moves one codon at a time, and the tRNA anticodon is always complementary to the mRNA codon. Watch for words like "always" and "directly" in options, because they often signal a false statement.