MCB 150 Lecture 33 Flashcards

Regulation in Bacteria

• Levels of β-gal, permease, and transacetylase can be adjusted post-transcriptionally.

  • The actual ratio of protein products is 10:5:2.

Adjustments from a Single mRNA

1. mRNA Stability:

   • Bacterial mRNAs have rapid turnover with a half-life of approximately 2 minutes, which allows for a quick response to environmental changes.

   • The degradation of lac mRNA from the 3′ end partly explains the protein ratio.

2. Translation Initiation:

   • The "strength" of the Shine-Dalgarno sequence affects the amount of protein produced from that gene.

   • β-gal > permease > transacetylase, which partly explains the ratio.

   • The availability of the Shine-Dalgarno sequence can be affected by proteins or secondary structures that block it.

The Tryptophan (trp) Operon

• The trp operon is on by default and is referred to as repressible because it can be turned off when tryptophan is abundant.

Other Examples of Regulation of Overall Protein Activity

• Allosteric regulation or feedback inhibition of proteins, exemplified by the regulation of PFK in glycolysis.

Reminders

• Regulation at the transcriptional level saves the most energy.

• Regulation at the post-translational level takes effect faster.

• These methods are balanced with regulation "in the middle" to produce the correct amount of functional protein under the given conditions.

Transcriptional Control in Eukaryotes

• Regulatory elements are key for transcriptional control in eukaryotes.