What are the three main components of the cytoskeleton and what are their main functions? correct answers Microfilaments: movement microtubules: transport of cellular materials
intermediate: support
What are the main similarities and differences between the three components of the cytoskeleton...
NROS 310 Exam 3 || with 100% Accurate Solutions.
What are the three main components of the cytoskeleton and what are their main functions?
correct answers Microfilaments: movement microtubules: transport of cellular materials
intermediate: support
What are the main similarities and differences between the three components of the
cytoskeleton? correct answers all are important for cytoskeleton structure
differ in size
Describe how the assembly of actin filaments is regulated. Include both the role of associated
protein and monomer concentration. correct answers Rac/Rho/CDC43 trigger Arp2/3 to
nucleate→ capping of (+) end→ grow filament via actin-ATP monomers→ stable filaments→
cap (-) end→ ADF breaks filament to actin-ADP monomers→ profilin phosphorylates
What would be the effect of incorporating a non hydrolyzable analog of ATP in the assembly
process? correct answers You would not produce any more actin monomers to feed the actin jet
What is the rate-limiting step in actin filament assembly? correct answers nucleation
Define critical concentration. correct answers The concentration where the probability of
addition happens just as easily as falling off
How do the ends of the actin filament differ? correct answers plus end vs minus end
each have their own concentration and probability of adding or taking off monomers
Also establishes a sense of direction for motor proteins to act on
What is dynamic instability? How does the regulation of ATP hydrolysis figure into the process?
correct answers the actin-ATP monomers within the polymer eventually become hydrolyzed that
makes it very difficult to add on and an overall unstable structure to hold together
How do the properties of actin subserve both stable and dynamic functions in the cell? correct
answers the ability to be phosphorylated to make stable polymers and networks but also the
ability to be broken down
What are the main functions of the different classes of actin associated proteins? correct answers
Capping proteins= prevents assembly and disassembly at plus end
Tropomodulin= prevents assembly and disassembly at minus end
Gelsolin= severs filaments and binds to plus end
Cofilin= binds ADP-actin filaments and accelerates disassembly
Profilin= bind subunits, prevents assembly
, Thymosin= binds subunits and prevents assembly
WASP + ARP 2/3= nucleates assembly and remains associated with minus end
Why are there motor proteins associated with both actin filaments and microtubules but not
intermediate filaments? correct answers actin filaments and microtubules construct a highway for
motor proteins while intermediate filaments are used for structural support
How does the hydrolysis of ATP cause myosin to move along the actin filament? correct answers
myosin heads hydrolyze ATP and become reoriented and energized
Why is it important that each individual myosin head group is only transiently attached to the
actin filament? correct answers to allow the muscle to be relaxed/ stretch/ not be contracted all
the time
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 skeletalmuscle, could you tell if the muscle was
contracted or relaxed? What would you see ifthere was a difference? C.) Predict the functional
effects of a defect in titan correct answers Cap Z binds the plus end of actin to the Z disc,
tropomodulin binds the minus end of actin, titin binds myosin to the Z disc.
B) you could tell if a mmuscle is contracted because you would see less lighter color thin
filament sections and more darker sections where actin and myosin overlap
C) a defect in titan would make it so that if the muscle was stretched too far, myosin would be
out of reach to attach to actin and the cell would not be able to contract
Describe how an increase in calcium causes the contraction of skeletal muscle and smooth
muscle. What are the key differences? correct answers Skeletal: Calcium binds to troponin which
then pushes tropomyosin out of the way so that the binding sites on actin are exposed and
myosin attaches.
Smooth: Calcium and CaM turn MLCK active which then phosphorylates Myosin LC and
contraction takes place
You have created a new transgenic mouse in which the troponin complex is nowindependent of
calcium regulation. What would happen in the skeletal muscles of these mice if troponin was
A.) never activated or
B.) always activated. correct answers A) contraction would never occur
B) contraction would always occur given there was sufficient ATP
Rigor mortis is the stiffening of the muscles that occurs after death. It results from an increase in
the level of Ca++ and a lack of ATP in the dead muscle cells. (Assume that all of the protein
components of the muscle remain intact.)
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