Unit 3--Lecture 16 (Microbial Regulatory Systems P2)

Question 1

Sigma Factor Regulation

Answer 1

Bacteria often use alternative sigma factors

These can be controlled by:
–altered transcription
–translation
–proteolysis
–anti-sigma factors

Examples: heat shock, sporulation, flagella synthesis

Question 2

Endospore Formation

Answer 2

Sigma cascade

Pro-sigma processing

Anti-sigma factors

2 components expressing different genes
—-use different strategies
—-talk using sigma factors

Mother cell uses pro-sigma factors released by endospore

Endospore uses anti-sigma factors provided by mother cell

Question 3

Small Regulatory RNA

Answer 3

Found within bacterial intergenic regions and regulate the transcription or stability of mRNA

The antisense nature of sRNA allows these molecules to bind mRNA

Can either stabilize the target mRNA or make it susceptible to degradation

Question 4

DNA Rearrangement

Answer 4

Some microbes use gene regulation to periodically change their appearance in a process called phase variation

Occurs by gene inversion

Invertible promoter switch regulates two genes encoding different flagellin types

H1 & H2: flagellin antigen

Question 5

Integrated Control Circuits

Answer 5

Chemotaxis is a behavior in which motile bacteria swim toward favorable environments (chemo attractants) or away from unfavorable environments (chemorepellents)

Question 6

Bacterial Motility

Answer 6

The direction of flagellar motor rotation determines the type of movement:
—-CCW rotation: results in smooth swimming
—-CW rotation: produces tumbling

Methyl-accepting chemotaxis proteins (MCPs)

Sensitivity set by methylation

Question 7

Mechanism of Chemotaxis

Answer 7

Red: CCW
Green: CW

Mutation in green:
–will never be able to switch
–always run red

Mutation in red:
–will not stop switching

Either way = non-motile
–broke chemotaxis

Question 8

Nitrogen Regulation

Answer 8

Nitrogen is often a limiting factor

Glutamine synthase (GlnA) uses nitrogen (NH4+) to convert glutamate into glutamine

Glutamine in excess: cell has lots of nitrogen

Glutamate in excess: cell is nitrogen-starved

Question 9

GlnA Regulation

Answer 9

Genetic control
—-transcription control

Two component
—-turn on when starving (glutamate in excess)

Biochemical control

Post-translational

Question 10

Quorum Sensing

Answer 10

Bacteria respond to cell density

It was discovered in Vibrio fischeri, a bioluminescent bacterium that colonizes the light organ of the Hawaiian squid

Question 11

Quorum Sensing Mechanism

Answer 11

Induction requires the accumulation of a secreted small molecule called an autoinducer
—-Gram (-): homoserine lactones
—-Gram (+): small peptides

Question 12

Genomics and Proteomics

Answer 12

Transcriptome: constitute all of a cell’s mRNA molecules

Proteome: constitute all of a cell’s proteins

Question 13

Gene Arrays

Answer 13

DNA microarray technology can simultaneously examine the expression of every gene in the cell

Uses a tool called a DNA microchip
—-DNA fragments from every ORF in genome are affixed on a solid support
—-DNA microchip can be used to analyze RNA extracted from microbes grown under different environmental conditions
—-first, complementary DNA (cDNA) is made

Question 14

Gene Chips

Answer 14

Label cDNA 1 red
Label cDNA 2 green

Mix and anneal to chip

Red + Green = Yellow (mix)
Dark = not expressed by either

Quantitate

Question 15

Two Dimensional Gels

Answer 15

Two-dimensional gel electrophoresis is used to view and capture fluctuations in the proteome
—-the first dimension separates proteins by their isoelectric point (charge)
—-the second dimension further separates them by molecular weights