Lecture Notes - Chapter 10 of Microbiology: An Evolving Science
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Course
General Microbiology (BIOM122)
Institution
University Of California - Irvine
Typed lecture notes covering chapter 10 of Microbiology: An Evolving Science, the textbook used in the "General Microbiology" course (BioM122) at UCI. Aligns with lecture 14. Skips over section on the Lac Operon.
Regulation of Bacterial Processes (skip Lac Operon
section) (Ch. 10, Lec. 14)
Saturday, November 7, 2020 6:51 PM ACTIVE LEARNING (11/9/2020)
• Cells have to be ready to give environmental responses (osmotic stress, temp change).
• Transcriptional, translational, post-translational control.
• Extracellular signal is relayed intracellularly once sensor kinase is phosphorylated (uses
• Gene regulation occurs at multiple levels: alteration of DNA sequence, control of transcription, mRNA ATP). Phosphorylation --> turns signal on.
stability, translational control, postranslational control. ○ Dephosphorylation is just as important --> turns signal off.
• Biofilms: microbes found in plaque on our teeth. Bacteria attached to surfaces exposed to
water.
○ Slow growing, but grow together to survive harsh environments. Stick together and
communicate.
•
• 16S rRNA: widely-used markers. Sequencing these will give us bacterial genomes.
○ Build primers at bacterial conserved regions. -> can build amplicons from there.
○ Need ribosomes -> cannot sequence viral genome.
• Taxonomic ranks: microbes are placed in a hierarchy where each level share a common
set of features. Domain -> phylum -> class -> order -> …
○ Genus name, species epithet. Ex. E. coli
• Control at the DNA level is the most drastic and least reversible. While at the protein level it is the most ○ The type strain can tell whether the bug is benign or ever growing.
rapid and most reversible. • Species: Collection of strains (fine-level differences b/w microbes in the same species).
10.1: Transcription Repressors and Activators • Phylogenetic trees:
• Key aspects of transcription control: (1) DNA-binding regulatory proteins that control initiation of ○ Rooted: all species has a common ancestor. Organized w/ an outgroup.
transcription at gene promoters, (2) environmental changes within/outside the cell that affect regulatory ○ Unrooted: species are not particularly related.
protein activity. ○ Distance of lines are approximates of time.
• Regulatory proteins: control initiation of bacterial transcription. Bind DNA at/near gene promoters, • The # of sequence differences b/w 2 species should be proportional to the time of
stimulate/prevent binding of RNA polymerase to promoter, contain a DNA-binding domain that interacts divergence b/w them. TRUE-- mutations accumulate over time.
w/ major groove of DNA.
○ Bind at sites that usually exhibit a sequence symmetry that involves an inverted repeat.
(palindromes?)
○ Each subunit of the regulatory protein dimer binds to half the symmetrical DNA sequence.
○ *Sequence of DNA affects the binding affinity of the regulatory proteins.
• Cells use different mechanisms to sense and respond to changes in intercellular and extracellular
conditions.
• Once ligands are bound to regulatory proteins, ligands alter the DNA-binding affinities of the regulatory
proteins, and thus their ability to stimulate/prevent transcription initiation at gene promoters.
• (plasma) Membrane-embedded signaling molecules detect extracellular conditions and inform the cell.
○ Extracellular conditions: osmotic stress, temp, sugars, amino acids, chemicals.
• Most microbes possess a 2-component signal transduction systems; each system regulates a
different set of genes.
• Many microbes are unicellular-- each cell needs an efficient system to detect extracellular conditions.
• The 2-component systems are based on protein phosphorylation:
○ Sensor kinase: membrane-bound enzyme; binding (to) an environmental signal causes kinase to
transfer a phosphate group from ATP to itself (or another target protein). Phosphorylated =
activated.
○ Response regulator: a cytosolic (in cytoplasm) protein stimulated by an activated sensor kinase;
binds to DNA and alters gene expression.
• Controlled by COVALENT modifications.
○
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