27 exam-style questions on Gene expression — topic D2.2 of Continuity and change in the IB Biology syllabus — with answers and explanations. Samples below; the full set is free with an account.
In eukaryotes, transcription of a gene is switched on when a specific regulatory protein binds a DNA control sequence. State the general name for such a protein.
Answer: Transcription factor
Transcription factors bind regulatory sequences such as promoters and enhancers to control whether RNA polymerase initiates transcription of a gene.
Which chemical modification of DNA, occurring mainly at cytosine bases in CpG islands, typically silences gene expression?
Answer: Methylation
DNA methylation adds methyl groups to cytosines in CpG islands, generally condensing chromatin and reducing transcription of the associated gene.
Acetylation of histone tails generally increases gene expression. Explain which change best accounts for this effect.
Answer: It loosens chromatin so DNA is accessible
Histone acetylation neutralises positive charges on histone tails, reducing their grip on DNA so the chromatin becomes more open (euchromatin) and more accessible to transcription factors.
During post-transcriptional processing of a eukaryotic pre-mRNA, which process removes introns and joins exons together?
Answer: Splicing
Splicing, carried out by the spliceosome, excises non-coding introns and ligates the coding exons to form mature mRNA.
Alternative splicing of a single gene's pre-mRNA increases proteome diversity. Determine the best explanation for how this occurs.
Answer: Different exons combine into different mRNAs
Alternative splicing joins different subsets of exons, so one gene can yield several distinct mRNA transcripts and therefore several different polypeptides.
The set of chemical modifications to DNA and histones that affect gene expression without altering the base sequence is collectively called the:
Answer: Epigenome
The epigenome comprises heritable chemical marks, such as DNA methylation and histone modification, that regulate gene expression without changing the DNA sequence itself.
That was 6 of 27 Gene expression questions.
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27 Gene expression questions — free with an account. Spaced repetition, streaks and full exam simulations included.
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