Bacterial Nutrition, Genomes and Regulation of Gene Expression

Question 1

Prototrophs:

Answer 1

Organisms that have no growth requirements beyond simple C, N and S sources.

Question 2

Auxotrophs:

Answer 2

Organisms that require added molecules to the growth medium.

Question 3

General Secretory System:

Answer 3

GSS

• Transports proteins to the gram+ extracellular space or to the gram- periplasm.
• Located in cytoplasmic membrane and recognizes precursor proteins with signal peptide.

Question 4

Glycerol transport in gram-:

Answer 4

Mediated by glycerol facilitator protein found in cytoplasmic membrane.
- Once inside kinase phosphorylates glycerol, trapping it.

Question 5

Galactose transport in gram-:

Answer 5

• ATP-dependent active transport.
• Uses more energy than group translocation.
• Shock sensitive because gal binding protein is in the perplasmic space.

Question 6

Group translocation:

Answer 6

• Works by trapping a sugar-phosphate within the cell.
• Complex of phosphotransferases which transfer phosphate groups from PEP to sugar as it crosses the cytoplasmic membrane.

Question 7

Pathogenicity islands:

Answer 7

Cluster of genes encoding proteins involved in pathogenesis.

Question 8

Types of RNA (4):

Answer 8

1. rRNA
2. tRNA
3. mRNA
4. microRNA (sRNA)

Question 9

Consensus sequence:

Answer 9

The sequence found most frequently in a survey of a large number of sequences.
- For promoters, the more similar a sequence is to the consensus, the stronger the promoter.

Question 10

Shine-Dalgarno sequence:

Answer 10

• Ribosome binding site

- Present in the 5’ nontranslated region of all prokaryotic mRNA’s.

Question 11

Streptomycin:

Answer 11

1. Blocks assembly of 70s initiation complex.

2. Causes misreading by ribosomes that have passed through initiation stage.

Question 12

Tetracyclines:

Answer 12

Block the binding of charged tRNAs to the acceptor site.

Question 13

Chloramphenicol:

Answer 13

Binds peptidyltransferase and blocks the peptidyltransferase reaction.

Question 14

Erythromycin:

Answer 14

Blocks the translocation step of translation.

Question 15

Negative inducible transcriptional control:

Answer 15

Operon normally turned off until an inducer molecule binds to the represser and inactivates it.

Question 16

Negative repressible transcriptional control:

Answer 16

Operon normally turned on since the repressor is inactive; a co-repressor must bind to repressor to yield a functional repressor which turns off transcription.

Question 17

Positive inducible transcriptional control:

Answer 17

No transcription because activator is inactive; co-activator binds to activator to yield a functional complex.

Question 18

Positive repressible transcriptional control:

Answer 18

Activator protein is functional in the absence of inhibitor and transcription occurs; in the presence of an inhibitor, the activator is inactivated and no expression occurs.