D2.2 Gene Expression
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What is gene expression?
The process by which information in DNA is used to produce a functional product (protein or RNA) via transcription and translation.
What does it mean when a gene is “switched on” or “off”?
On: Gene is transcribed → mRNA → protein produced Off: No transcription → no protein produced
What controls gene expression in eukaryotes?
Transcription factors that bind to DNA regulatory regions (promoters + enhancers).
What is a promoter?
A DNA sequence upstream of a gene where RNA polymerase binds to start transcription.
What is an enhancer?
A DNA region (often far from gene) where transcription factors bind to increase transcription rate.
Why are transcription factors essential in eukaryotes?
RNA polymerase cannot bind directly to DNA → transcription factors are required to recruit it.
How is gene regulation different in prokaryotes?
RNA polymerase binds directly to promoter Genes organized into operons Controlled by repressors
What is an operon?
A cluster of genes controlled together with: Promoter Operator Structural genes
What is the operator?
A DNA region acting as an on/off switch where repressors bind to block transcription.
What causes cellular differentiation?
Different genes are expressed in different cells → different proteins → different functions.
What is the transcriptome?
The full set of mRNA molecules produced in a cell.
What is the proteome?
The full set of proteins produced by a cell.
Role of transcription factors in differentiation?
They determine which genes are expressed → produce different proteins → lead to specialized cell types.
Why is mRNA degraded after use?
Prevents overproduction of proteins Allows rapid regulation of gene expression Enables dynamic response to environment
What is epigenetics?
Regulation of gene expression by modifications that do NOT change DNA sequence.
What are epigenetic tags?
Chemical modifications (e.g., methyl groups) that affect gene expression.
What are histones?
Proteins DNA wraps around to form chromatin.
Effect of histone acetylation?
Reduces positive charge Loosens DNA-histone interaction Increases transcription (gene active)
Effect of histone methylation?
Tightens chromatin Decreases transcription (gene inactive)
What is DNA methylation?
Addition of methyl groups to cytosine bases.
Effect of DNA methylation?
Prevents transcription factor binding OR Condenses chromatin → Gene silencing
Relationship between methylation and gene expression?
High methylation → low expression Low methylation → high expression
How does environment affect gene expression?
Through epigenetic changes (e.g., methylation).
(environment/epigenetics) Example: air pollution and gene expression?
Increased methylation of genes (e.g., Foxp3) → higher asthma risk.