Certain genes or parts of genes can be turned on and off to achieve a very specific output.

• Transcription factors can bind to specific gene sequences and either activate or repress transcription.
• The regions of DNA are bound by transcription factors are either called promoters, enhancers, or silencers.
• Promoters are regions where RNA polymerase binds to initiate transcription.
• Enhancers are regions where the rate of transcription is increased.
• Silencers are able to slow down the rate of transcription.

Increased transcription rates = more gene expression = more of the desired protein.

Everything discussed above with regards to gene regulation has to do with eukaryotic cells.

Regulation of genes in prokaryotes:

• Related prokaryotes are typically grouped together into operons, which are transcribed together under the control of one promoter.
• Positive regulation: Repressorproteins bind to operators, preventing RNA polymerase from initiating transcription.
• Negative regulation: Activator proteins bind to operators, enhancing RNA polymerase binding, increasing transcription.

Classic Olympiad Gene Regulation Example:

• Lac operon in bacteria functions with 3 structural genes (lacZ, lacY, and lacA).
• When lactose is present, it binds to the lac repressor, preventing it from binding to the operator, allowing for transcription.
• When lactose is absent, there is nothing to block the repressor from binding to the operator, so transcription is stopped (no enzymes are produced to digest lactose).
• Note: Bacteria prefer glucose as opposed to lactose!

Written by Josephine Ankomah