Regulating Gene Expression (College Board AP® Biology): Flashcards
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Define regulatory proteins.
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Define regulatory proteins.
Regulatory proteins are proteins that bind to specific base sequences in DNA to switch gene expression on or off, e.g. transcription factors.
Define regulatory sequences.
Regulatory sequences are stretches of DNA that regulatory proteins bind to in order to control transcription, e.g. promoters.
What is the difference between constitutive and inducible genes?
Constitutive genes are always expressed (e.g. housekeeping genes needed for basic cell function)
Inducible genes are expressed only when required (e.g. enzymes for digesting lactose)
Define epigenetic changes.
Epigenetic changes are reversible modifications to DNA or histones that affect gene expression without changing the DNA base sequence, e.g. DNA methylation and histone acetylation.
True or False?
Methylation of DNA increases the rate of transcription.
False.
Adding methyl groups to DNA reduces transcription rates, lowering gene expression.
Adding acetyl groups to histones is called and increases the rate of transcription.
Adding acetyl groups to histones is called acetylation and increases the rate of transcription.
How does the regulation of gene expression lead to cell differentiation?
Differentiation occurs when the genes for tissue-specific proteins are expressed, so that different cell types (e.g. muscle vs nerve cells) arise from the same genome.
Which two factors about gene products determine an organism's phenotype?
The function of the gene products
The amount of gene product produced
Define operon.
An operon is a cluster of genes controlled by a single promoter and operator, so that genes needed for the same function are transcribed together as one mRNA.
What is the difference between an inducible and a repressible operon?
Inducible operons are normally off and are switched on by an inducer
Repressible operons are normally on and are switched off when the end product is abundant
In an inducible operon such as the lac operon, how does the presence of lactose switch the structural genes on?
Lactose binds to the repressor, preventing it from binding to the operator.
This allows RNA polymerase to transcribe the structural genes, so the enzymes are produced.
How can eukaryotic genes that are dispersed across different chromosomes be coordinately regulated?
They share regulatory sequences that bind the same transcription factor, so a single transcription factor can activate them together (e.g. heat-shock genes during stress).
Define transcription factors.
Transcription factors are proteins that bind to regulatory DNA sequences (such as promoters or enhancers) to control whether a gene is transcribed.
How do activator and repressor transcription factors differ in their effect on transcription?
Activators help recruit or stabilize RNA polymerase binding, increasing transcription
Repressors block RNA polymerase from binding or moving along the DNA, reducing transcription
True or False?
Enhancers must be located directly next to the promoter to increase transcription.
False.
Enhancers can lie far upstream, downstream, or within introns; the DNA loops around so bound transcription factors contact the promoter and stabilize RNA polymerase.
What determines the phenotype of a cell or organism at the molecular level?
Which genes are expressed and at what levels, because expressed genes are transcribed and translated into proteins that determine the cell's structure, function, and behavior.
True or False?
All cells in a multicellular organism contain the same DNA but express different sets of genes.
True.
Every cell carries the full genome, but differential gene expression activates different genes in different cell types, producing distinct proteins.
Define differential gene expression.
Differential gene expression is the process by which different sets of genes are switched on or off in different cells, so that each cell type makes its own specific proteins despite sharing the same DNA.
How does selective gene expression lead to cell differentiation?
In a stem cell, some genes are activated and others inactivated. Only active genes are transcribed into mRNA and translated into proteins.
These proteins are specific to the cell type, giving the cell its specialized structure and function.
During differentiation, mRNA is transcribed only from genes within a cell.
During differentiation, mRNA is transcribed only from active genes within a cell.
Define development.
Development is the process by which a fertilized egg develops into a multicellular organism, requiring expression of the right genes at the right time, place, and sequence.
What role do transcription factors play in development?
Transcription factors coordinate development by turning sets of genes on or off in the correct sequence, controlling when and where genes are expressed.
genes encode transcription factors that control body plan development.
Hox genes encode transcription factors that control body plan development.
Where do RNA polymerase and transcription factors bind to initiate transcription?
To promoter or enhancer DNA sequences, which can lie either upstream or downstream of the transcription start site.
How do negative regulatory molecules inhibit gene expression?
They bind to DNA and block transcription, preventing the gene from being expressed.
How do small RNA molecules such as microRNAs and siRNAs regulate gene expression?
They act post-transcriptionally by binding to complementary mRNA sequences, leading to:
mRNA degradation, preventing translation
blocking ribosome binding, reducing protein synthesis
True or False?
Small RNA molecules regulate gene expression before transcription begins.
False.
Small RNAs act post-transcriptionally, binding to mRNA to trigger its degradation or block ribosome binding, adding another layer of control over protein amounts.
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