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VICBiologyQuick questions
Unit 3: How do cells maintain life?
Quick questions on Gene structure and regulation (trp operon): VCE Biology Unit 3
15short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is parts of a eukaryotic gene?Show answer
Promoter. A non-coding region upstream of the start of transcription. It contains binding sites for transcription factors and RNA polymerase, often including a TATA box. The promoter is not transcribed; it positions the polymerase.
What is regulator genes?Show answer
A regulator gene codes for a protein (often a transcription factor) that controls the expression of one or more target genes. Regulator gene products may be:
What is the trp operon (worked prokaryotic example)?Show answer
An operon is a cluster of genes under a single promoter, transcribed as one mRNA. They are common in prokaryotes such as Escherichia coli.
What is promoter?Show answer
A non-coding region upstream of the start of transcription. It contains binding sites for transcription factors and RNA polymerase, often including a TATA box. The promoter is not transcribed; it positions the polymerase.
What is exons?Show answer
The coding regions, retained in the mature mRNA and translated. The order of exons (and their alternative combinations through splicing) determines the protein sequence.
What is introns?Show answer
Non-coding regions inside the gene, transcribed into pre-mRNA but removed by the spliceosome during RNA processing.
What is terminator?Show answer
A sequence at the 3' end that signals RNA polymerase to release the transcript.
What is regulatory elements?Show answer
Enhancers and silencers (further from the gene) can be bound by transcription factors that increase or decrease the rate of transcription.
What is when tryptophan is low?Show answer
The repressor stays inactive and does not bind the operator. RNA polymerase transcribes the operon, the five enzymes are made, and tryptophan is synthesised.
What is when tryptophan is high?Show answer
Tryptophan acts as a corepressor and binds the trp repressor. The repressor changes shape and now binds the operator. RNA polymerase is blocked, transcription stops, and the cell stops making more tryptophan.
What is predicted change?Show answer
Within minutes, tryptophan binds the trp repressor; the active repressor binds the operator; RNA polymerase is blocked; trp mRNA levels fall; production of the biosynthesis enzymes (trpE through trpA) slows; tryptophan synthesis declines.
What is if a mutation deletes the operator?Show answer
The repressor has nothing to bind, so the operon is transcribed continuously regardless of tryptophan levels. Tryptophan will be over-produced.
What is saying the regulator gene is inside the operon?Show answer
It is a separate gene at a different location. The operon contains the promoter, operator and structural genes.
What is forgetting introns are in the pre-mRNA?Show answer
Introns are transcribed; they are removed during processing. Prokaryotes generally do not have introns and do not splice mRNA.
What is mixing promoter and operator?Show answer
The promoter is where RNA polymerase binds; the operator is where the repressor binds.