L2: Genome to Phenotype

Question 1

Some signals are ‘tangible’. What does this mean?

Answer 1

Perceptible by touch, e.g. nutrients.

Question 2

What does catabolite repression mean?

Answer 2

Preferential utilisation of the best carbon and energy source.

Question 3

In E. coli, catabolite repression is performed in diauxic growth. What does this mean?

Answer 3

It represses the enzymes needed for lactose utilisation whilst glucose is being used.

Question 4

Does E.coli use glucose or lactose first?

Answer 4

Glucose

Question 5

What does CRP stand for?

Answer 5

cAMP Receptor Protein.

Question 6

What does CAP stand for?

Answer 6

Catabolite Activator Protein.

Question 7

What is the difference between CAP and CRP?

Answer 7

They are the same thing.

Question 8

Describe the molecular mechanism that uses glucose as an energy source.

Answer 8

1. Glucose is transported into the cytoplasm by EII Glc and is phosphorylated by cytoplasmic IIA Glc, forming glucose-6-phosphate.
2. Molecule can enter metabolism.
3. Dephosphorylated IIA Glc binds to LacY on the membrane - blocks lactose transport.
4. LacI is a repressor protein that binds to the lac operon and prevents the transcription + translation of lac Z, Y and A.
5. cAMP not synthesised; CRP not used.

Question 9

Describe the molecular mechanism that uses lactose as an energy source, when glucose has been used.

Answer 9

1. IIA Glc remains phosphorylated - activates adenylate cyclase - synthesises cAMP from ATP.
2. cAMP interacts with CRP and binds to the promoter region of the lac operon. Allows transcription + translation of the lactose metabolising enzymes.
3. Lactose enters the cell via LacY and binds LacI to prevent it from repressing the operon.

Question 10

Define the term ‘operon’.

Answer 10

A segment of DNA with a set of genes that will always be transcribed under the control of an operator.

Question 11

Define a ‘local regulator’.

Answer 11

Controls the expression of one operon/ gene.

Question 12

Define a ‘global regulator’.

Answer 12

Many targets.

Question 13

Define the term ‘regulon’.

Answer 13

Set of operons that fall under the control of a specific (global) regulatory protein.

Question 14

What is a receptor gene?

Answer 14

A gene that can detect and measure the levels of gene expression.

Question 15

Define the term ‘quorum sensing’.

Answer 15

The regulation of gene expression in response to population density.

Question 16

Why do many bacteria use quorum sensing?

Answer 16

The system ensures sufficient numbers before initiating activities that are cell density dependent. For example, the production of a toxin.

Question 17

Species that employ QS produce a signal-specific molecule called an?

Answer 17

Autoinducer.

Most common form = Acyl Homoserine Lactones.

Question 18

QS promotes biofilm formation, in which?

Answer 18

Bacteria attach to a surface and aggregate to form a colony.

Question 19

What is the QS system used by EHEC called? What does it control?

Answer 19

QseCB. Controls many genes include Ler, which is a local regulator that in turn controls 4 lee operons, which in turn result in type III secretions.

Question 20

What type of regulatory response system is QS?

Answer 20

Two component regulatory system.