KAL - Transcriptional Control in Prokaryotes

Question 1

What is gene density?

Answer 1

The number of genes per MB

Question 2

What is the major way protein expression is controlled?

Answer 2

Transcriptional Control

Question 3

What is the difference between constitutive expressed genes and regulated genes (in bacteria)?

Answer 3

Constitutive expressed genes

• Genes which are continuously expressed, also known as housekeeping genes

Regulated genes

• Genes which can be turned on or off based on demands and the environment

Question 4

How are bacterial promoters recognised?

Answer 4

Binding of RNA polymerase to sequences around -35 and -10

Question 5

What 4 subunits are present in bacterial RNA polymerase?

Answer 5

1. Ɑ subunits (x2)
2. β subunit
3. β’ subunit
4. σ subunit

Question 6

Which subunit ensures promoter specificity?

Answer 6

σ subunit

Question 7

What are the 2 main methods of transcriptional control in bacteria?

Answer 7

1. Alternative sigma factors
2. Transcriptional regulators

Question 8

When are the use of alternative sigma factors used in control?

Answer 8

During extreme conditions

Question 9

What does negative regulation involve?

Answer 9

Transcriptional repressors

• Bind to the operator sites and prevent the binding of RNA polymerase

Question 10

What does positive regulation involve?

Answer 10

Transcriptional activators

• Bind to specific regions which helps RNA polymerase binding

Question 11

What are operons?

Answer 11

Regions of DNA that contain clusters of related genes

Question 12

What do the 3 structural genes do in the lac operon?

Answer 12

• β Galactosidase cleaves lactose into its component sugars
• Permease transports lactose into cells
• Transacetylase covalently modifies lactose

Question 13

What is the function of the Catabolite Activator Protein (CAP) in the lac operon?

Answer 13

Factilitates the binding of RNA polymerase to the promoter region

• Active at low glucose, high lactose levels