Chapter 8 (3)

Question 1

Global control: The stringent response

Answer 1

In natural environments, nutrients appear/disappear rapidly.
Stringent response: global control mechanism triggered by amino acid starvation

Question 2

Global control: The stringent response- Alarmones

Answer 2

Triggered by (p)ppGpp
Alarmones: produced by ReIA to signal amino acid starvation
-rRNA and tRNA synthesis decreases
-amino acid synthesis increases
Achieves balance between protein production and protein catabolism

Question 3

Other global control networks

Answer 3

Responses involving lots of genes, regulons, etc...
Several other global control systems
-aerobic and anaerobic respiration
-catabolite repression
-nitrogen utilization
-oxidative stress
-SOS response
-heat shock response

Question 4

Other global control networks: Heat shock response

Answer 4

Heat shock response: largely controlled by alternative sigma factors
-heat shock proteins: counteract damage of denatured proteins and help cell recover from temperature stress
Heat shock response also occurs in archaea

Question 5

Cell differentiation: Sporulation in Bacillus

Answer 5

Regulation of development in model bacteria
-some prokaryotes display basic principle of differentiation
Endospore formation in Bacillus
-controlled by 4 sigma factors
-forms inside mother cell
-triggered by adverse external conditions

Question 6

Cell differentiation: Caulobacter

Answer 6

Two forms of cells:
-swarmer cells: dispersal role
-stalked cells: reproductive role
Controlled by three major regulatory proteins
-external stimuli and internal factors play a role in affecting life cycle

Question 7

RNA based regulation

Answer 7

Regulatory RNA molecules base pairing with mRNA

• double stranded region prevents translation
• small RNA’s called antisense
• antisense RNA can regulate multiple mRNA’s
• transcription of antisense RNA enhanced when target genes need to be turned off
• some antisense RNA’s actually enhance translation

Question 8

RNA based regulation: RNA chaperones

Answer 8

Binding of antisense RNA to targets depends on a small protein

• small proteins called RNA chaperones
• -RNA chaperone: Hfq
• -Hfq binds to both RNA molecules and to ribonuclease E
• Helps small molecules maintain correct structure

Question 9

RNA based regulation: Riboswitches

Answer 9

Riboswitches: RNA domains in an mRNA molecule that can bind small molecules to control translation of mRNA

• Located at 5’ end of mRNA
• Binding results from folding of RNA into 3D structure
• similar to a protein recognizing a substrate
• -found in some bacteria, fungi and plants

Question 10

RNA based regulation: Attenuation

Answer 10

Premature termination of mRNA synthesis
-after start of transcription, but before end
-tryptophan operon in E. coli
-mRNA stem-loop structure and synthesis of leader peptide determining factors
Genomic evidence suggests attenuation in archaea.

Question 11

Excess tryptophan

Answer 11

Transcription terminated and tryptophan structural genes not transcribed

Question 12

Limiting tryptophan

Answer 12

Transcription continues and tryptophan structural genes transcribed