Gene Structure and RNA Processing Components

Steps:

• Recall that eukaryotic genes contain exons (coding regions) and introns (non-coding regions removed during splicing).
• Identify primary transcript as the initial RNA copy (pre-mRNA) including both exons and introns before processing.
• Examine diagram labels: P likely marks coding areas, Q the unprocessed RNA, R non-coding parts, S intervening sequences.
• Match labels to definitions: only S aligns with non-coding sequences like introns.

Why D is correct:

• Non-coding sequences are DNA/RNA regions without protein-coding function, such as introns, per central dogma of molecular biology.

Why the others are wrong:

• A: Introns are specifically non-coding regions spliced out, but P labels exons or other coding parts.
• B: Primary transcript is pre-mRNA with introns; Q labels mature mRNA or DNA template.
• C: Exons are coding regions retained in mRNA; R labels introns or untranslated regions.

Final answer: D