Catabolite Repression

Definition

Catabolite repression is a regulatory mechanism in bacteria where the presence of a preferred carbon source, such as glucose, inhibits the expression of genes involved in the metabolism of less favorable carbon sources. This allows the bacteria to prioritize the utilization of the most energy-efficient carbon source available.

5 Must Know Facts For Your Next Test

1. Catabolite repression allows bacteria to prioritize the utilization of the most energy-efficient carbon source, such as glucose, over less favorable carbon sources.
2. The presence of a preferred carbon source triggers the activation of the cAMP receptor protein (CRP), which in turn represses the transcription of genes involved in the metabolism of alternative carbon sources.
3. Catabolite repression is mediated by the phosphorylation state of the enzyme Enzyme IIA (EIIAGlc) of the phosphotransferase system (PTS), which senses the availability of glucose.
4. When glucose is present, EIIAGlc is dephosphorylated, leading to the inhibition of adenylate cyclase and the subsequent decrease in cAMP levels.
5. The decrease in cAMP levels results in the inactivation of the CRP, which can no longer bind to and activate the promoters of genes involved in the metabolism of alternative carbon sources.

Review Questions

• Explain how catabolite repression allows bacteria to prioritize the utilization of the most energy-efficient carbon source.
  • Catabolite repression is a regulatory mechanism in bacteria that allows them to prioritize the utilization of the most energy-efficient carbon source, such as glucose, over less favorable carbon sources. When a preferred carbon source like glucose is present, it triggers the activation of the cAMP receptor protein (CRP), which in turn represses the transcription of genes involved in the metabolism of alternative carbon sources. This is mediated by the phosphorylation state of the enzyme Enzyme IIA (EIIAGlc) of the phosphotransferase system (PTS), which senses the availability of glucose. When glucose is present, EIIAGlc is dephosphorylated, leading to the inhibition of adenylate cyclase and the subsequent decrease in cAMP levels. The decrease in cAMP levels results in the inactivation of the CRP, which can no longer bind to and activate the promoters of genes involved in the metabolism of alternative carbon sources. This allows the bacteria to focus their metabolic resources on the most energy-efficient carbon source available.
• Describe the role of cyclic AMP (cAMP) and the cAMP receptor protein (CRP) in the mechanism of catabolite repression.
  • Cyclic AMP (cAMP) and the cAMP receptor protein (CRP) play a crucial role in the mechanism of catabolite repression. When a less preferred carbon source is available, cAMP levels increase, and cAMP binds to the CRP. The cAMP-CRP complex then activates the transcription of genes involved in the metabolism of the alternative carbon source. However, when a preferred carbon source like glucose is present, the phosphorylation state of the Enzyme IIA (EIIAGlc) of the phosphotransferase system (PTS) changes, leading to the inhibition of adenylate cyclase and a decrease in cAMP levels. This decrease in cAMP levels results in the inactivation of the CRP, which can no longer bind to and activate the promoters of genes involved in the metabolism of alternative carbon sources. This allows the bacteria to prioritize the utilization of the most energy-efficient carbon source available.
• Analyze how the mechanism of catabolite repression allows bacteria to adapt their metabolism to changing environmental conditions and optimize their energy production.
  • The mechanism of catabolite repression allows bacteria to adapt their metabolism to changing environmental conditions and optimize their energy production. By prioritizing the utilization of the most energy-efficient carbon source, such as glucose, over less favorable carbon sources, bacteria can maximize their energy output and conserve resources. This is achieved through the regulation of gene expression, where the presence of a preferred carbon source triggers the activation of the cAMP receptor protein (CRP), which in turn represses the transcription of genes involved in the metabolism of alternative carbon sources. The decrease in cAMP levels, mediated by the phosphorylation state of the Enzyme IIA (EIIAGlc) of the phosphotransferase system (PTS), is the key signal that allows bacteria to sense the availability of the preferred carbon source and adjust their metabolic pathways accordingly. This adaptive response ensures that bacteria can efficiently utilize the most energy-rich carbon sources, optimizing their energy production and survival in changing environmental conditions.

Related terms

Catabolic Pathways: Metabolic pathways that break down complex molecules into simpler ones, releasing energy in the process.

Operon:

A group of genes that are transcribed and regulated together as a single unit in prokaryotes.

Cyclic AMP (cAMP): A secondary messenger molecule that plays a crucial role in catabolite repression by activating the transcription of genes involved in the metabolism of less preferred carbon sources.