Chapter 18
Test Hints

The College Board loves to test on the operon so 30% of this test will involve the operon (to help you get in shape for the AP test in May). Therefore, you must know the operon very, very well. Remember- it is a way to control gene expression. This chapter illustrates operons in prokaryotes- not Eukaryotes. Operons exist in eukaryotes but the trp operon and the lac operon are only found in bacteria.
•Be able to distinguish between an inducible and a repressible operon. How are they fundamentally different from one another? Make sure you clearly understand this.

Repressible Operon (Know the trp operon as an example)
What is the overall purpose of a repressible operon?
Know the function of the regulatory gene.
Know what an inactive repressor is, know how it is made active.
Know what a corepressor is and how it works (in this case it is tryptophan).
Know the function of a promoter.
Know the function of an operator.
Know that the operon includes the promoter, operator, and the genes of the operon.
Know what the genes of the trp operon do (i.e. what is their function?)

Inducible Operon (Know the lac operon as an example)
What is the overall purpose of an inducible operon?
Know the function of the regulatory gene.
Know what an active repressor is, know how it is made inactive.
Know what an inducer is and how it works (in this case it is allolactose).
Know the function of a promoter.
Know the function of an operator.
Know that the operon includes the promoter, operator, and the genes of the operon.
Know what the genes of the lac operon do (i.e. what is their function?)


The way in which prokaryotes recombine DNA is very different from eukaryotes. Remember crossing-over during meiosis? Remember independent assortment during meiosis? Remember fertilization (recombining DNA from the female and the male)? These are the ways eukaryotes recombine their DNA in new ways. This is how they “mix it up”. Bacteria, because they are asexual, have found different ways to recombine DNA, i.e. “mix it up”. They do it in four different ways: transformation, transduction, conjugation, transposition. Make sure you can clearly distinguish between the different processes. 30% of the questions will be on these four concepts.

1. Know what transformation is.

2. Know what transduction is. (see figure 18.12)
•Know the difference between the two types: generalized and specialized (I’ve decided you need to be aware of specialized transduction- it isn’t hard, just check out figure 18.12 and you will see how it differs from generalized transduction)
•Know what a prophage is.

3. Know what conjugation is. (see figure 18.14)
•Know what the F factor is.
•Know what an episome is.
•Know about plasmids. Know what an F plasmid is.
•Know what an F+ cell is and what an F- cell is.
•Know what an Hfr cell is.
•Know what an R plasmid is.

4. Know what a transposon is. (be familiar with the basics- look at figures 18.15, 18.16, 18.17)
•Realize that a transposon is simply a way of moving genes around within a single organism- not between organisms.
•Transposons can move around within the main chromosome of a bacteria or between the main chromosome and the same bacteria’s plasmids (or vice versa).


The remaining 30% of the test will be on the following material.

Know the difference between the lytic and lysogenic cycles. Study figures 18.4 and 18.5 well. Know the difference between a temperate and a virulent virus. What is meant by a “temperate virus”?
Know what a prophage is. Oh, I already reminded you about this. Better know it well!

Know the life cycle of the Human Immunodeficiency Virus (HIV)
Know that it is a retrovirus. Know what is meant by retrovirus.
Remember what the “Central Dogma” is and why it is no longer true!

Know what a prion is.

Know what a viroid is.

According to EO Wilson, what is the best species on earth? (answer is in the reading in the HW section- read it (it is a very short reading)!)

The free response could be any of the questions but since the College Board loves to test you on the operon I would study that question very, very carefully!

Good luck to you all.