HELP ME 1
As a struggling premedical student, worried about tip-top performance
on the MCAT so that you have a chance of attending some podunk medical
school, you are concerned about taking standardized multiple choice
tests and especially about the problem that, even when you know the
correct answer, in a multiple-choice testing situation the incorrect
answer is chosen. (By the way, there is no medical school in Podunk.
Podunk is a small town about 70 miles south of Des Moines that has a
single gas station/general store.) You have decided to investigate the
biological basis of the ability to properly choose answers on
multiple-choice exams. After months of laborious effort, you have
discovered a microscopic structure that seems to be implicated in this
process, buried deep in the cerebral cortex, shaped like a roulette
wheel, which you have dubbed the "intellisome". When given a multiple
choice question, the intellisome spins, selects an answer directed by
various neural inputs, then dissociates and needs to be reconstructed
for the next question. The trouble, it seems, is that the intellisome
can assemble in two ways, such that it spins either clockwise or
counterclockwise. When the intellisome is assembled to spin clockwise,
it then selects the appropriate answer. But when the intellisome is
assembled to spin counterclockwise, it selects the opposite and
inappropriate answer. So you've decided to do a molecular analysis of
the intellisome assembly, in hopes of assuring that the intellisome
always assembles in the correct, clockwise configuration. (And then
maybe you'll get into medical school.)
By culturing cells from the cerebral cortex of human cadavers, you
have found that an individual clone of cells will always produce
either clockwise or counterclockwise intellisomes, but not both. You
have isolated the DNA encoding one of the protein components of the
intellisome, gene ismF. Remarkably, while the DNA of the ismF gene is
the same in the cells (CCW cells) producing counterclockwise
intellisomes as in all the other tissues of the body, DNA of the ismF
gene isolated from cells (CW cells) producing clockwise intellisomes
has a different structure. The restriction enzyme maps of the ismF
genes isolated from these two cells is shown below.
(diagram available at this website/the second question towards the
bottom of the page)
http://biohelpme.blogspot.com/
Under most circumstances, the orientation of intellisome produced by a
clone of cells is fixed. However, if you give a brief pulse of
dopamine, a proportion of the clockwise intellisome cells will start
producing counterclockwise intellisomes and vice versa. This altered
intellisome assembly is stable until another pulse of dopamine is
administered. You, of course, decide to investigate this switching
phenomenon more critically, hoping that you can figure out how to lock
the cells in the clockwise synthetic mode. (And you drop the thought
of going to medical school. After all, if this works and you patent
it, you can make a mint selling it to future premeds.)
You have isolated RNA for the ismF gene from CW and CCW cells and
hybridized each RNA to the DNA for ismF genomic DNA isolated both from
CW and CCW cells. The hybridization was done under conditions where
both RNA/DNA and DNA/DNA form, but RNA/DNA hybrids are favored. You
have taken resultant hybrids and spread them on EM grids for analysis
in the electron microscope. Shown on the next page are representive
images of the hybrids seen in these conditions (thick lines represent
double-stranded nucleic acid; thin is single-stranded; the numbers
indicate the length of the corresponding stretch of double-stranded
nucleic acid.)
From this data, hypothesize what happens to the ismF gene when the
intellisome orientation switches and explain how the presumed protein
product of the ismF gene differs between clockwise and
counterclockwise intellisomes |
