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39 Cards in this Set

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Components of the cytoskeleton
Microtubules, intermediate filaments, and actin microfilaments
Functions of the Cytoskeleton
structural support, cell motility, cell division, translocation of subcellular organelles, regulation of protein synthesis
T or F: The cytoskeleton is a statis entity
FALSE
What support structure is under the plasma membrane? What is this entity composed of?
The membrane cytoskeleton. It is composed of microfilaments, cross linking proteins and transmembrane proteins.
Where are microtubules and intermediate filaments located in a cell?
Distributed throughout the cytoplasm.
What is the major component of microfilaments?
Actin
Size of Actin filaments
7nm
Energy source for actin polymerization
ATP hydrolysis
3 phases of actin polymerization
Nucleation, elongation, steady state
What is required for actin nucleation to initiate?
3 monomers of Actin bound together to form a nucleation seed
What is the rate limiting step for polymerization of microfilaments and microtubules?
Nucleation
Which side of a microfilament polymer does actin add to?
Both! The + end is faster growing, though.
Describe the structure of Actin.
Globular protein, 41000 molecular weight
T or F: Actin polymerization also depends on the presence of K+ and Mg++ salts.
TRUE
Why is polarity important in a microfilament?
It is important in structures that produce movement.
Give 2 examples of actin arrays.
Thin filaments of contractile muscles. Microvilli
T or F: Actin filaments generally polymerize in a similar fashion.
False. Different Actin Binding Proteins generate a host of differing structures.
What are myosins and what do they do?
Actin Binding Proteins that produce movement through the hydrolysis of ATP.
T or F Actin filaments are extremely important for cell motility.
TRUE
List the following Actin Polymers in increasing order of stability: Microvilli, Contractile Ring, Lemellipodia, Thin Fillments of Contractile Muscles
Contractile Ring < Lemellipodia < Microvilli < Contractile Muscle thin filament
How do myosin and actin work together for muscle contraction?
Power stroke of myosin when attached to actin. Energy comes from hydrolysis of ATP.
Microtubule size
24nm
What protein makes up microtubules and what do they look like?
Tubulin, a dimer. Long hollow rod with 13 dimers per turn.
What provides the energy for microtubule polymerization?
GTP
What are MAPs?
Microtubule Associated Proteins that can stabilize or crosslink the structure.
T or F: Microtubules are stable, rigid structures.
False, they are labile.
What is the MTOC and what does it do?
Microtubule Organizing Center. Contains two centrioles and forms mitotic spindle apparatus.
How do microtubules play an important structural role?
Help maintain the cell's shape.
What reinforces the shape of dendrides in neurons?
Microtubules
What is cilia made of and describe it's structure?
The core (axoneme) consists of a circle of 9 microtubule doublets (each with a complete and incomplete microtubule). In addition 2 microtules are in the center of the structure.
How does a cilia move?
Dyneins located on the completed microtubule reach out to adjacent doublet and "walk". ATP is hydrolized for the motion.
Flagella vs. Cilia
Flagella are longer and usually are found one per cell. Mainly for motion while cilia function to move fluids past a surface. Made of the same complex.
Kinesins vs. Dyneins: Motion along microtubules?
Kinesins travel away from the nucleus while Dyneins trael toward the nucleus on microtubules.
What are the major fibers of the mitotic spindle?
Microtubules
Size of intermediate filaments
10nm
T or F: Intermediate filaments are polar.
False. Unlike microtubules and actin, they are non-polar.
T or F: Polymerization of intermediate fibers does not require hydrolysis of ATP or GTP.
TRUE
Are intermediate filaments stable or labile?
They can be either.
What intermediate filament proteins are in epithelial cells? The membrane cytoskeleton? In muscles?
Keritins in epithelial. Lamins in the membrane. Desmin in the muscles. Others include vimentin in fibroblasts, spetins in contractile ring, and neurofillaments in glial fibrillary.