Module 4: Section 3C

Question 1

Signal transduction in eukaryotic cells

Answer 1

A ligand binds to a cell surface receptor, triggering phosphorylation cascades that activate transcription factors, which then enter the nucleus to turn genes on or off

Question 2

Signal transduction in bacterial cells

Answer 2

• Bacteria detect external signals like ligands, which are interpreted by cell machinery to influence gene expression
• Signals must cross membranes to reach DNA, and since bacteria lack nuclei, their pathways are simpler than in eukaryotes

Question 3

Steps in the GAC System (P. aeruginosa gene regulation) - 1

Answer 3

• Host signals interact with the cytoplasmic membrane protein (GacS)
• Becomes activated via phosphorylation to form GacS-P

Question 4

Steps in the GAC System (P. aeruginosa gene regulation) - 2

Answer 4

• GacS-P transfers its phosphate to GacA which becomes GacA-P
• GacA-P is now an activated transcription factor and enhances transcription of microRNAs

Question 5

Steps in the GAC System (P. aeruginosa gene regulation) - 3

Answer 5

These microRNAs control whether or not RsmA binds to its target promoter regions

Question 6

Steps in the GAC System (P. aeruginosa gene regulation) - 4

Answer 6

In absence of GAC activity, RsmA enhances transcription of acute virulence genes and suppresses genes linked to chronic infections

Question 7

Steps in the GAC System (P. aeruginosa gene regulation) - 5

Answer 7

• Activated GAC causes microRNAs to bind RsmA, blocking it from gene promoters
• This allows chronic infection virulence factors to be expressed while acute ones are repressed

Question 8

What is quorum sensing in P. aeruginosa?

Answer 8

It’s a gene regulation system using signaling molecules called homoserine lactones (HSLs) that control virulence based on cell density

Question 9

What are the two main HSLs in P. aeruginosa and what do they do?

Answer 9

• 3-oxo-C12-HSL (made by LasI) and C4-HSL (made by RhlI)
• They are transported out of the cell but re-enter once external high concentrations are reached to activate transcriptional regulators LasR or RhlR, turning on virulence genes

Question 10

What happens when LasR and RhlR bind HSL molecules?

Answer 10

HSL-bound LasR and RhlR activate their own transcription, increasing their levels and promoting expression of multiple virulence factors

Question 11

Autoinduction

Answer 11

Both HSLs can up regulate the expression of their own genes

Question 12

Hierarchical regulatory network

Answer 12

• The LasR network “primes” the cell by controlling expression of the C4-HSL system
• Allows for apid activation of many virulence factors when C4-HSL re-enters the cell

Question 13

Virulence factors regulated via LasR

Answer 13

Regulated by LasR, Exotoxin A inhibits protein synthesis in host cells, causing severe tissue and organ damage

Question 14

Virulence factors regulated via RhIR

Answer 14

• Pyocyanin creates reactive oxygen species that damage host cells and help form biofilms
• It can lyse some bacterial cells in CF lungs, and the released DNA further strengthens biofilm formation

Question 15

HIV genome - gag, pol and env genes

Answer 15

3 major genes that code for structural and enzymatic proteins

Question 16

HIV genome - tat and rev genes

Answer 16

Encode important regulatory proteins

Question 17

HIV genome - remaning genes

Answer 17

Contribute estrutural and regulatory functions

Question 18

HIV genome - 5’-LTR and 3’-LTR

Answer 18

• regions at either end of the genome
• Important for regulation of gene expression

Question 19

Tat protein

Answer 19

• Viral protein
• Tat binds to a stem-loop at the 5′ end of viral RNA and activates transcription by promoting elongation from the viral long terminal repeat (LTR)

Question 20

Rev protein

Answer 20

Rev transports mRNAs for viral structural proteins from the nucleus to the cytoplasm, increasing how quickly viral proteins are made

Question 21

How does HIV control translation of its proteins?

Answer 21

• HIV uses multicistronic transcripts (like pol) to encode multiple proteins from one RNA and produces large amounts of viral mRNA to outcompete host mRN
• It can also make proteases that block host protein translation