Which of the Following Events Occurs During Transcription?

The answer

The event that occurs during transcription is that RNA polymerase synthesizes a complementary strand of messenger RNA (mRNA) using one DNA strand as a template. The enzyme reads the DNA template strand in the 3'→5' direction and builds the new RNA in the 5'→3' direction, inserting uracil (U) wherever the template has adenine, because RNA has no thymine.

In eukaryotes, transcription also includes RNA processing: the initial transcript (pre-mRNA) gets a 5' cap and a poly-A tail, and non-coding introns are removed by splicing while the coding exons are joined. So depending on the answer choices, both "mRNA is synthesized from a DNA template" and "introns are removed" can be correct transcription-stage events.

Why the other options are wrong

The distractors typically describe translation or DNA replication, not transcription:

• "tRNA brings amino acids to the ribosome" or "a polypeptide is assembled" — these happen during translation, after mRNA leaves the nucleus. Ribosomes, tRNA, and amino acids belong to protein synthesis, not RNA synthesis.
• "DNA polymerase copies the entire genome" or "two identical DNA molecules are produced" — that is DNA replication, which uses DNA polymerase and produces DNA, not RNA.
• "Anticodons pair with codons" — again translation, occurring at the ribosome.

The key discriminators: transcription uses RNA polymerase (not DNA polymerase), produces RNA (not protein or a second DNA copy), and occurs in the nucleus of eukaryotes (translation occurs at ribosomes in the cytoplasm).

The three stages

Transcription proceeds in three phases:

1. Initiation — RNA polymerase binds the promoter, a DNA sequence (such as the TATA box) upstream of the gene, with the help of transcription factors. The DNA unwinds.
2. Elongation — RNA polymerase moves along the template strand, adding complementary RNA nucleotides 5'→3'. Behind it, the DNA double helix re-forms.
3. Termination — the polymerase reaches a terminator sequence and releases the finished RNA transcript.

The promoter matters because it tells the polymerase where to start and which strand to read, setting the gene's orientation.

Transcription vs. translation

Keep the two central processes straight. Transcription copies a gene's DNA into mRNA inside the nucleus, using RNA polymerase; the "language" stays nucleic acid. Translation then reads that mRNA at the ribosome and builds a protein, converting the nucleotide language into an amino-acid language via tRNA and the genetic code. Transcription comes first and makes the message; translation comes second and reads it. Any answer involving ribosomes, tRNA, codon-anticodon pairing, or amino acids is describing translation, so it cannot be the transcription event.