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Final Exam- BIO 251 Quiz Questions with Verified Solutions
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Final Exam- BIO 251 Quiz Questions with VerifiedSolutions
1) Actin is one of the most evolutionarily conserved proteins. What does this tell you about
the structure and function of this protein in eukaryotic cells? Correct Answer-
Evolutionarily conserved-hasn't undergone much change since existence of eukaryotes.
Tells us that this protein is vital for cellular function. Tells us it can do a variety of functions in
cells.
Its so conserved because it is very important for cells. Multifunctional makes it more well-
conserved because monomers that make it. Up are very simple, and are able to combine in. a
complex way to perform its many functions. It has to be something to do with the fact that so
many other proteins can bind to it. G-actin has lots of aa side chains that stick out. Sequence
of aa side chains make it multifunctional. Every different protein that binds to actin has to
bind to a specific place on actin. Mutation in aa side chains could negatively impact the
binding.
1) I mentioned phalloidin is a toxic produced by the deathcap mushroom. It is toxic because it
binds across two actin monomers and holds them together. In contrast, latrunculin, another
toxin - this one is made in sponges - tightly binds to G-actin monomers. Describe the effect
each drug would have on actin treadmilling. Correct Answer-Phalloidin-filaments will
continue to elongate, unable to take filaments off of chain. Prevents depolymerization.
Polymerization would stop for this when the cell reaches below some threshold of free G-
actin.
, Final Exam- BIO 251 Quiz Questions with Verified
Solutions
Latrunculin- would bind. To. G-actin, prevent polymerization, stop force against PM, length of.
F-actin would get shorter because there would be depolymerization but not polymerization.
Level of monomers in cell may make depolymerization slow down
1) Let's think about the stages of death. If you were a crime scene investigator and you were
examining a body at ambient temperature, you'd probably know the following:
If the body feels warm and no rigor is present, death occurred under 3 hours before.
If the body feels warm and stiff, death occurred 3-8 hours earlier.
If the body feels cold and stiff, death occurred 8-36 hours earlier.
If the body is cold and not stiff, death occurred more than 36 hours earlier.
Rigor refers to rigor mortis, which is the stiffening of a body after it dies. Knowing what you
know about cellular respiration and myosin's ATPase cycle and muscle function, please
answer the following questions: What is the basis of rigor mortis? Why is it referred to as
stiffening and not contracting? Why does it take 3 hours for stiffening to occur? Why does the
rigor retreat? Correct Answer-Basis of rigor mortis- after ATP hydrolyzed, and after
everything else takes place, ATP stops. In death, ATP runs out, causes muscles to be stiff
because no ATP to release myosin head from actin.
Stiffening instead of contracting-myosin is not moving actin filaments along, myosin is. Bound
to actin and is immovable. No cycle of contraction, so will only be stiff
, Final Exam- BIO 251 Quiz Questions with Verified
Solutions
Why 3 hours-there will still be some ATP left over which will be used up until it is gone.
Why does rigor finally go away?- the body begins to decay so the proteins will be degraded,
releasing the myosin from the actin. actin fibers fall apart, myosin heads degrade, becomes
pliable again
1) You know that cancer cell migration is a key part of metastasis, which is the deadliest
aspect of cancer. So, you want to develop a drug that can inhibit cancer cell migration. You
know that myosin-2-based contraction is required for cell migration and so you specifically
want to develop a drug to inhibit it, myosin-2. (Note: the myosin-2 that promotes migration is
very similar to but ultimately a different isoform from muscle myosin-2. The non-muscle
myosin-2 forms smaller filaments that are more dynamic, whereas the myosin-2 thick
filaments in muscles are very stable and larger structures.)
a) What aspect of migration is myosin-2 involved in. Think about the steps of migration
discussed in lecture (and see figure 17-33 in your text). Where is the force being produced
that involves myosin-2? Correct Answer-Myosin-2 is involved in retraction (back end of
cell). Force being produced is where actin brings up end of cell back into middle
a) You develop a drug that seems to inhibit myosin-2, but you are unsure of its mechanism of
action. In general, how might you know whether the drug blocks ATP from binding to myosin
, Final Exam- BIO 251 Quiz Questions with Verified
Solutions
versus allowing ATP to bind but blocking hydrolysis? Can you think of a way to test this in a
biochemical assay with purified actin and myosin-2? Correct Answer-You could track the
amount of free ATP, if there was a comparatively low amt it would be binding and if there was
a high amount, it wouldn't be. If ATP cannot bind, youd have the same amount of ATP in your
solution as you started with. Control-without drug
Your control, the ATP would decrease after going through the cycle
Experimental-ATP levels would stay higher if ATP binding was prevented by the drug.
If you carried out the same experiment, could you tell whether it was able to bind but not
able to hydrolyze? No- ATP levels would stay the same as compared to when you first put it in.
depends on ratio concentration of ATP to actin and myosin.
Another experiment- generate michaelis menten curve-keep myosin levels the same, change
levels of ATP, see if drug competitively inhibits it. Kd value would increase if it affected ATP
binding. But cannot analyze whether atp was bound or not to myosin
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