Question 1 (29 points)
Barney is an alien. On his ship, hidden in the Stata building, you find alien bacteria that
metabolize wood. You call this species
, and call your original strain BLT (for
“Barney’s little termiticus”).
You subject a sample of BLT to mutagens, and isolate a new strain that no longer metabolizes
wood. You conclude that you have succeeded in disrupting at least one gene necessary to
metabolize wood. You call the mutant strain M.
You mix a sample of M with a sample of heat-killed wild type BLT, and the resulting strain
metabolizes wood. You summarize your data in the following table:
Heat-killed BLT +M
Did the content of any of the BLT or M cells change in the experiment?
If yes, which cells
underwent the change, and what change occured? If not, explain why there was no change.
Some cells of type M underwent the change. They acquired some of the genetic material from the heat-
killed BLT cells. In particular, some part of the genetic material they acquired encoded for the gene that
was mutated in M. Having received this gene, M cells now behave like the wild-type BLT cells because
they can now produce the agent (like the Earth proteins) that restores the wood metabolism pathway.
You plan to characterize the alien genetic material. You start by breaking some
cells open to determine their molecular composition. You find that they contain various small
molecules, carbohydrates, lipids, and two other macromolecules, A and B.
In order to determine which macromolecule is the carrier of genetic information, you repeat
your previous experiment, but include test tubes where you treat the sample of the heat-killed
BLT with either an agent that destroys macromolecule A (A-ase) or macromolecule B (B-ase).
You find the following results (including the repeat of your previous experiment in the first 4
Strains and agents
Heat-killed BLT +M
A-ase treated heat-killed BLT +M
B-ase treated heat-killed BLT +M
b) Which molecule is the carrier of genetic information in
? Justify your answer.
B is the carrier of genetic information in the alien organism. This is because when the BLT cells are
treated with B-ase, no B remains in the sample, and, as a result, no transformation occurs. On the other
hand, treatment with A-ase has no bearing on the transformation ability of the heat-killed BLT cells. We,
therefore, must conclude that B is the carrier of genetic information.