Lac operon mutations and partial diploids.
Supplemental Instruction
IowaStateUniversity / Leader: / Matt C.
Course: / Biol/Gen 313
Instructor: / Dr. Myers & Dr. Vollbrecht
Date: / 04/02/2017

Introduction: This worksheet discusses material covered in the twenty-eighth lecture(03/29/2017). Chapter12examines these topics.

Concepts

  1. Lac operon mutations.
  2. Partial diploids.

Material

  1. Lac operon mutations.

In this section, we’ll do some abbreviated practice with lac operon mutants.

  1. Last time, we talked about the I- knockout mutation. This produces a non-function lac repressor. If I+ is wild-type, what do you suppose an IS mutant might do? Note that this is differentiated from I-.
  1. How could mutation of the lac operator affect operon transcription?
  1. How could mutation of the CAP site affect operon transcription?
  1. In the following scenarios, decide what is transcribed in the absence and in the presence of lactose (allo-lactose).
  1. lacPI+, lacI-, lacP+, lacO+, lacZ+, lacY+
  1. lacPI+, lacI-, lacP-, lacO+, lacZ+, lacY+
  1. lacPI+, lacI+, lacP+, lacOC, lacZ-, lacY+
  1. lacPI+, lacI+, lacP+, lacOC, lacZ-, lacY-
  1. lacPI+, lacI-, lacP+, lacO+, lacZ+, lacY+
  1. lacPI-, lacI+, lacP+, lacO+, lacZ+, lacY+
  1. lacPI+, lacIS, lacP+, lacO+, lacZ+, lacY+
  1. Assume CAP is permanently bound. If the lac repressor is knocked out (made non-functional) is the operon still inducible?
  1. Partial diploids.

Here we’ll examine partial diploidy in prokariotes.

  1. How does partial diploidy arise in prokaryotes?

  1. What beneficial effects can partial diploidy bring? What negative effects could it cause?
  1. Describe the difference between trans-acting and cis-acting operon constructs.
  1. Similar to the previous section, here are some partial diploid examples. Decide what is transcribed in the presence of and in the absence of lactose. (allo-lactose).
  1. lacPI+, lacI-, lacP+, lacO+, lacZ+, lacY+

lacPI+, lacI+, lacP+, lacO+, lacZ+, lacY+

  1. lacPI+, lacI+, lacP+, lacO+, lacZ+, lacY+

lacPI-, lacI+, lacP-, lacO+, lacZ+, lacY+

  1. lacPI+, lacI+, lacP+, lacO+, lacZ+, lacY+

lacPI+, lacI-, lacP+, lacOC, lacZ+, lacY-

  1. lacPI+, lacI-, lacP+, lacOC, lacZ+, lacY+

lacPI+, lacIS, lacP+, lacO+, lacZ+, lacY+

Things to do next

  • Focus your review on things that were difficult from this worksheet. If it was really challenging, don’t worry; these are meant to be tough and push your understanding of the topics we covered.
  • The lac operon is common fare for test questions which is why we’re spending this much time with it. We’ll catch up on the material from lecture 29 next time.
  • If you have any questions, ask me in session, in class, or by email. I’m more than happy to help.
  • Next session will be on Tuesday (04/04/2017) from 6:10 to 7:00 PM in Gilman 2109. We will be covering material from Friday’s and Monday’s lectures.