Biology (university) · Part 05
Gene regulation and biotechnology
How cells switch genes on and off, and the lab tools that cut, copy and edit DNA.
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- Lac operonA group of bacterial genes switched on together to digest lactose. A repressor protein blocks the genes unless lactose is present. When lactose is there, it binds the repressor, which lets go, and the genes turn on.
- Transcription factorA protein that binds DNA near a gene and helps or blocks RNA polymerase. Activators raise transcription. Repressors lower it. Enhancers are DNA sites where activators bind, often far from the gene.
- Epigenetic modificationChemical tags on DNA or on the histone proteins it wraps around that change how active a gene is, without changing the DNA letters. DNA methylation usually switches genes off.
- Restriction enzymeA bacterial enzyme that cuts DNA at a specific short sequence. Many leave overhanging single-strand ends ('sticky ends') that can pair with matching ends from other DNA.
- Recombinant DNADNA made by joining pieces from different sources. A gene is cut out, joined into a plasmid (a small circle of bacterial DNA) with DNA ligase, and put into bacteria, which copy it and make the protein.
- Polymerase chain reactionPCR copies a chosen stretch of DNA millions of times. Repeated cycles of heating (to separate strands), cooling (so primers bind) and warming (so heat-stable polymerase copies the DNA) double the amount each time.
- Gel electrophoresisA method to sort DNA pieces by size. DNA is negatively charged, so in an electric field it moves through a gel toward the positive end. Small pieces move faster and further.
- CRISPR-Cas9A gene-editing tool taken from bacterial defence against viruses. A guide RNA leads the Cas9 enzyme to a matching DNA sequence, where it cuts both strands. The cell's repair then disables or changes the gene.