Lecture 9

Question 1

What happens when RecA is activated?

Answer 1

It induces LexA to inactivate by self-cleavage (degradation). This derepresses the SOS system and allows DNA repair proteins to be produced.

Question 2

What is transposon mutagenesis?

Answer 2

A laboratory technique that uses transposons to create mutations. It is an enzyme-catalyzed process (DNA transposase). Because bacterial genomes contain relatively little noncoding DNA, most transposon insertions will occur in genes that encode proteins. This technique can be used to determine the function of a novel gene if a screening method is available.

Question 3

What are selectable mutations?

Answer 3

Mutations that confer some type of advantage under certain environmental conditions. They are easy to detect and isolate if you choose the right conditions.

Question 4

What are non-selectable mutations?

Answer 4

Mutations that cannot be selected for. They do not have an advantage or disadvantage under lab conditions (they might in nature). Finding these mutants in the laboratory requires a process called screening (i.e. looking for mutants within a population).