What are the three main components of the cytoskeleton and what are their main functions? correct answers Microtubules, microfilaments and intermediate filaments that help form the cytoskeleton to create stability, structure, and allow movement
What are the main similarities and differences betw...
NROS 310 Exam 3 FINAL || very Flawless.
What are the three main components of the cytoskeleton and what are their main functions?
correct answers Microtubules, microfilaments and intermediate filaments that help form the
cytoskeleton to create stability, structure, and allow movement
What are the main similarities and differences between the three components of the
cytoskeleton? correct answers Microfilaments: flexible, smallest, regulate motion, help stabilize,
polymerized from monomers to polymers
Microtubules: less flexible, wider, hallow, important for movement, more organized pattern,
Intermediate filament: less dynamic, many cells don't need them, specialized structures, good for
strength
Describe how the assembly of actin filaments is regulated. Include both the role of associated
proteins and monomer concentration. correct answers It is regulated by concentration of actin
monomers bumping into the filament and its a lot easier for a filament to build once there are
already some oligomers
The cell can regulate nucleation to make the filament grow or fall apart
The filament also has polarity and it is easier to add onto the plus end than the minus end
Describe how actin filaments bind and fall apart correct answers Actin binds together in the ATP
form and fall off in the ADP form
What would be the effect of incorporating a nonhydrolyzable analog of ATP in the assembly
process? correct answers The filaments would grow until it ran out of monomers
What is the rate-limiting step in actin filament assembly? correct answers Going from monomers
to oligomers, also called nucleation
Define critical concentration. correct answers The amount of actin in an ATP form that keeps the
actin from neither shrinking nor growing (i think)
How do the ends of the actin filament differ? correct answers One is positive, one is negative,
monomers will add faster to the positive end
What is dynamic instability? How does the regulation of ATP hydrolysis figure into the process?
correct answers The actin filament will grow when there are more ATP monomers and shrink
when they switch to ADP and they begin to fall off
As long as the filament has ATP on the ends, it stays stable, but once hydrolysis catches up and
the ends are in the ADP form, it begins to shrink
, If actin is so dynamically unstable, how can it function in a stable structure like skeletal muscle?
correct answers ARP 2/3 binds onto the minus end and covers it so actin monomers cannot fall
off and exposes the plus end so it can grow
A different capping protein binds onto the plus end to stabilize it
How do the properties of actin subserve both stable and dynamic functions in the cell? correct
answers It can be stable by putting caps on the ends but can change into dynamic structure if it is
cut in the middle and the ADP ends are exposed
What are the main functions of the different classes of actin associated proteins? correct answers
ARP 2/3: binds onto actin on the minus end and nucleates
Profilin: puts monomers in GTP form
Tropomyosin: stabilizes filament
Formin: binds onto actin on the plus end and nucleates
Thymosin: binds subunits to prevent assembly
Tropomodulin: Prevents assembly and disassembly at the minus end
Cofilin: Binds ADP actin filaments and accelerates disassembly
Gelsolin: severs filaments and binds to plus end
Capping protein: prevents assembly and disassembly at minus end
How does the hydrolysis of ATP cause myosin to move along the actin filament? correct answers
Myosin heads have bound phosphate and ADP, once it binds to actin, phosphate is released and
the power stroke happens, then ATP replaces ADP, causing the myosin head to detach, ATP is
hydrolyzed and re-cocks into the start position
Why is it important that each individual myosin head group is only transiently attached to the
actin filament? correct answers Because it needs to detach once it moves the filament forward so
it can grab onto another part of the actin and drag it forward
Diagram the components of a sarcomere in skeletal muscle. Identify the proteins involved
including actin, myosin, titin, CapZ, and tropomodulin. B.) If you looked at an electron
micrograph of skeletal muscle, could you tell if the muscle was contracted or relaxed? What
would you see if there was a difference? C.) Predict the functional effects of a defect in titan.
correct answers B. Yes, if there is a lot of overlap, the muscle is contracted
C. If titin was defective, the muscle could stretch too far and become damaged
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