The lac Operon

Question 0

Describe the lac operon

_____——–_______________________________
I | | P | O | Z | Y |
_____——–_______________________________

Answer 0

I - A regulatory gene
↪️Codes for a regulatory PROTEINS (which are the products of regulatory genes) and repressor proteins

They control STRUCTURAL GENES by switching them on/off - Transcription factors

Z/Y - Are structural genes
↪️ Codes for PROTEINS that are used in the body (e.g. Enzymes/Hormones)

P - The promotor region
↪️ Where RNA polymerase (makes complementary strands from DNA) binds at the start of transcription

O - Is the operator region
↪️ IT affects P ( A repressor protein will bind to O)

Question 1

Explain how ecoli saves energy

Answer 1

• only produce the enzymes to metabolise lactose if they are in an environment that contains lactose
• these enzymes are B galactosidase and lactose permease
• only producing the enzymes when they are needed saves energy (ATP)

Question 2

What does lac Y code for?

Answer 2

• codes for lactose permease

* embedded in membrane to make it permeable to lactose

Question 3

What does the lac Z gene code for?

Answer 3

• codes for B - galactosidase

* lactose –> glucose + galactose (catalysed by B - galactosidase)

Question 4

How does the lac operon work when there is no lactose present

Answer 4

• the repressor protein binds to the operator region, blocking the promotor region, so RNA polymerase cannot bind
• so transcription of Lac z and Lac Y is blocked so there is no mRNA made
• therefore no B-galactosidase or lactose permease is made

Question 5

How does the lac operon work when there is lactose present

Answer 5

• lactose binds to the repressor protein causing it to change shape so it can no longer bind to the operator region
• because the repressor protein is not bound to the operator region it no longer blocks the promoter region so RNA polymerase can now bind to the promotor region and transcribe lac Z and lac Y
• mRNA copies of lac Z and lac Y are made, so translation can occur and B-galactosidase and lactose permease can be synthesised
• ecoli can now break down lactose
• once all the lactose is broken down it can no longer bind to the repressor protein
- so the repressor protein binds to the operator region, blocking RNA polymerase from binding to the promotor region - stretching the genes off again