Cytoskeleton:
A) 3 main components
B) main functions correct answers A) actin filaments, microtubules, and intermediate filaments
B) actin - sense the environment and direct movement
microtubules - for transport
intermediate - help keep the cell shape, to anchor organelles
What are t...
NROS 310 Exam 3 || A+ Graded Already.
Cytoskeleton:
A) 3 main components
B) main functions correct answers A) actin filaments, microtubules, and intermediate filaments
B) actin - sense the environment and direct movement
microtubules - for transport
intermediate - help keep the cell shape, to anchor organelles
What are the main similarities and differences between the three components of the
cytoskeleton? correct answers Main similarities:
- all important for cytoskeleton structure
- MT & Fila: charged ends; form a highway for motor proteins
Main differences:
-size; function
Describe how the assembly of actin filaments is regulated. Include both the role of associated
proteins and monomer concentration. correct answers Rac/Rho/CDC43 trigger Arp 2/3 to
nucleate: capping of (+) end --> grow filament via actin-ATP monomers --> stable filaments -->
cap (-) end --> ADF breaks filament to actin-ADP filaments --> profilin phosphorylates
What would be the effect of incorporating a nonhydrolyzable analog of ATP in the assembly
process? correct answers Actin filaments would grow uncontrollably, there would be no dynamic
instability
- When broken by ADF you would not produce more actin monomers to grow more filaments,
you would also have now 2 filaments b/c basically every monomer added is an ATP-cap
What is the rate-limiting step in actin filament assembly? correct answers Nucleation, the
clumping together of ATP-actin
Define critical concentration. correct answers The concentration where addition happens just as
easily as falling off
- One concentration for the (+) end and one concentration for the (-) end
How do the ends of the actin filament differ? correct answers - (+) end and (-) end
- easier to add onto (+) end than it is to add onto the (-) end
What is the dynamic instability? How does the regulation of ATP hydrolysis figure into the
process? correct answers - switching between growing and shrinking
, - ATP's attached to the individual monomers eventually hydrolyze to ADP at random
- when hydrolysis catches up to addition, it is difficult to add to the (+) end, so addition must be
ahead of the hydrolysis for addition to continue
How do the properties of actin subserve both stable and dynamic functions in the cell? correct
answers - actin-ATP cap allows temporary stability to get more stability: add capping proteins
that mimic what ATP does for
- the stability of the entire A.F.
- Arp 2/3 can cap and still allow growth
What are the main functions of the different classes of actin associate proteins? correct answers -
providing stability
- reducing stability
- hydrolyzing ATP --> ADP and vice versa
- regulating nucleation
Why are there motor proteins associated with both actin filaments and microtubules but not
intermediate filaments? correct answers Because actin filaments and microtubules provide a
polar filament for the motor protein to walk on, which is the only type of filament that they bind
to. Intermediate filaments do not form polarized filaments, causing the motor protein to not
associate with them.
How does the hydrolysis of ATP cause myosin to move along the actin filament? correct answers
Each myosin head binds/hydrolyzes ATP, using energy of ATP hydrolysis to walk toward (+)
end
Why is it important that each individual myosin head group is only transiently attached to the
actin filament? correct answers They are attached only transiently to actin filament so as not to
interfere with one another--> you don't want muscles to contract all the time
Diagram the components of a sarcomere in skeletal muscle.
A) 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 A) look at notecard
B) Yes, you would see a shorter light band and a much longer dark band
C)Titan works like a spring that keeps the muscles from being pulled apart too far apart
--If defective, muscle contraction would be negatively affected; muscles could be pulled too far
apart and unable to contract again with no actin-myosin interaction
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