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Gene Expression Quiz
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Which classic DNA motif in some core gene promoters is recognised by transcription factors that help to initiate transcription?
- A Enhancer sequence that increases mRNA stability You picked ✕
- B TATA box that binds TFIID and positions RNA polymerase You picked ✓
- C Splice donor site that marks the start of an intron You picked ✕
- D Start codon that signals the beginning of translation You picked ✕
- E Polyadenylation signal that directs RNA cleavage and 3′ processing You picked ✕
Correct!
Incorrect
The answer is B: TATA box that binds TFIID and positions RNA polymerase
Explanation
Why B is correct
See Transcription. Option B is correct. Before a gene can be transcribed, RNA polymerase has to find where it starts. In eukaryotic cells (cells with a nucleus), this is done by a region called the promoter, a stretch of DNA at the start of a gene. Many promoters contain a short, recurring DNA sequence called a motif, and one classic motif is the TATA box, whose sequence is TATAAA and which sits about 25 to 35 bases before the start site. Transcription factors (proteins that help to switch genes on) recognise and bind to the promoter. The core complex, TFIID, includes a TATA-binding protein, and the other factors then assemble in turn and recruit RNA polymerase II, the enzyme that makes mRNA. The TATA box is rich in adenine and thymine bases, which are held together by weaker bonds, so the DNA unwinds easily at this spot. Not every gene has a TATA box; it is found in some promoters only. A helpful way to remember the name is that it is simply the base sequence, T to A-T to A, written in the DNA.
- Promoter: a stretch of DNA at the start of a gene where RNA polymerase begins.
- TATA box: the motif TATAAA, about 25 to 35 bases before the start site.
- Role: binds transcription factors, which recruit RNA polymerase II.
Why the other options are incorrect
- A. Enhancer sequence that increases mRNA stability: Enhancers are DNA elements that bind transcription factors and increase how often a gene is transcribed. They influence transcription rate rather than mRNA stability, and they are not the core promoter motif. Your answer
- C. Splice donor site that marks the start of an intron: The splice donor site marks the start of an intron in the pre-mRNA. It is used during splicing after transcription and is not a promoter element. Your answer
- D. Start codon that signals the beginning of translation: The start codon (AUG) is found in the mRNA and signals where translation begins. It is not a DNA promoter element recognised by transcription factors. Your answer
- E. Polyadenylation signal that directs RNA cleavage and 3′ processing: The polyadenylation signal marks where the RNA is cleaved and the poly(A) tail is added at the 3′ end. It acts after transcription, on the RNA, not at the start of the gene. Your answer
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1
Which statement best explains how the correct amino acid is added to a growing polypeptide chain during translation?
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2
Which feature of mRNA ensures that the correct amino acid is added to a growing polypeptide chain during protein synthesis?
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