Read How RNA Becomes a Message
Gene expression depends on DNA control sequences, RNA processing and the template requirements of each enzyme.
RNA Processing and Gene Expression is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Process RNA correctly
Eukaryotic pre-mRNA splicing removes introns and joins exons; snRNA is part of the nuclear spliceosome. Mature bacterial mRNA aligns continuously with its generally uninterrupted gene, so intron loops are absent. In bacteria, translation can begin while transcription continues.
Distinguish regulatory sequences and enzymes
Promoters and operators are DNA control sites, usually noncoding, that bind regulatory proteins. DNA polymerase and RNA polymerase require DNA templates; reverse transcriptase can copy RNA, while polynucleotide phosphorylase and poly-A polymerase do not require DNA. Replication and transcription both use DNA templates and complementary pairing, but transcription copies only a gene/region.
Why protein diversity exceeds gene count
Alternative RNA splicing allows one gene to produce different transcripts, and post-translational processing can yield different mature polypeptides. Mutation and meiotic recombination change inherited sequences or combinations but do not by themselves explain the systematic excess of polypeptide products over gene number.
Understand cooperative transcription activation
A transcription factor that binds a promoter or upstream regulatory sequence can recruit a second factor. If protein Q binds DNA only when protein P is present, P is the DNA-binding recruiter; Q can still be required for activation. Binding evidence and activation evidence are related but distinct.
Expression and operon control
Mature-mRNA-derived cDNA represents genes expressed in the sampled cells and lacks introns. In the trp operon, tryptophan acts as a corepressor: the activated repressor binds the operator and stops transcription.
OlympIQ exam lens
- ✓Splicing removes introns and joins exons.
- ✓snRNA acts in the nuclear spliceosome.
- ✓Bacterial transcription and translation can be coupled.
- ✓Promoter/operator are regulatory DNA sequences.
- ✓Alternative splicing expands transcript/protein possibilities per gene.
- ✓Post-translational processing can create distinct mature proteins.
Do not reverse the terms: introns are removed; exons remain in mature RNA.
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