Gene Control (Cambridge (CIE) A Level Biology): Flashcards
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Define structural gene.
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Define structural gene.
A gene that codes for a protein used in the cell's metabolism or structure (e.g. an enzyme or structural protein) — not involved in regulating other genes.
Define regulatory gene.
A gene that codes for a protein (such as a repressor or transcription factor) that controls the expression of other genes.
Define inducible enzyme.
An enzyme that is normally absent and is only synthesised when its substrate (inducer) is present.
Define repressible enzyme.
An enzyme that is normally produced, but whose synthesis is switched off when the end-product accumulates.
What is the key difference between structural and regulatory genes?
Structural genes code for proteins used in metabolism or structure.
Regulatory genes code for proteins that control the expression of other genes.
A gene that codes for a protein controlling the expression of other genes is a gene.
A gene that codes for a protein controlling the expression of other genes is a regulatory gene.
What is an operon?
A group of genes controlled by a single promoter and operator, which are transcribed together (found in prokaryotes).
What does the lac operon control?
The production of enzymes (including β-galactosidase) that allow E. coli to metabolise lactose.
What is the operator in the lac operon?
A region of DNA next to the structural genes where the repressor protein can bind to block transcription.
In the lac operon, what happens when lactose is absent?
The regulatory gene produces a repressor protein.
The repressor binds to the operator, blocking RNA polymerase, so the structural genes are not transcribed and no enzymes are made.
In the lac operon, what happens when lactose is present?
Lactose binds to the repressor protein, changing its shape so it can no longer bind the operator.
RNA polymerase can now transcribe the structural genes, so the enzymes to metabolise lactose are made.
Are the lactose-metabolising enzymes inducible or repressible?
Inducible — they are only made when lactose (the inducer) is present.
When lactose is absent, the protein binds to the operator and blocks transcription.
When lactose is absent, the repressor protein binds to the operator and blocks transcription.
What are transcription factors?
Proteins that bind to DNA and control gene expression in eukaryotes by increasing or decreasing the rate of transcription.
Transcription factors are proteins that bind to to control the rate of transcription.
Transcription factors are proteins that bind to DNA to control the rate of transcription.
True or False?
Transcription factors can only decrease the rate of transcription.
False.
Transcription factors can increase or decrease the rate of transcription.
What is the role of DELLA proteins?
They are repressors that inhibit the factors which promote transcription, keeping certain genes switched off.
How does gibberellin activate genes?
Gibberellin causes the breakdown of DELLA protein repressors.
This releases the transcription factors that promote transcription, so the target genes are switched on.
Gibberellin activates genes by causing the breakdown of protein repressors.
Gibberellin activates genes by causing the breakdown of DELLA protein repressors.
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