L18/19: Gene Regulation

Question 1

At what levels are constitutively genes expressed

Answer 1

• Expressed at low levels in the cell - but all the time

Question 2

At what levels are environmentally-regulated genes expressed?

Answer 2

• Expressed at very high or very low levels - high levels dependent on an environmental signal

Question 3

What else can be found in operons?

Answer 3

• A regulatory region called the operator (O) can be found either upstream or downstream (and sometimes overlapping) the promoter)
• the regulatory protein binds here

Question 4

What are lac and mal operons examples of?

Answer 4

• Catabolic operons

Question 5

When do the cells need to synthesize the proteins in the mal or lac operons?

Answer 5

• If maltose or lactose is present

- The proteins produced in these operons function to break down (catabolize) the sugars

Question 6

What are the 3 levels of expression and their meanings?

Answer 6

High:

• Gene/operon is transcribed at high levels
• i.e. RNA Pol (& transcription factors) bind strongly/tightly and often to the promoter to initiate transcription
• e.g. lac operon when lactose is present and mal operon when maltose is present

Basal (low):

• Gene/operon is minimally transcribed
• i.e. RNA Pol binds weakly and rarely to the promoter and transcription is not initiated very often.
• e.g. lac operon when lactose is absent and mal operon when lactose is absent

Zero:

• No transcription / not possible
• Not functional