Chapter 17 - Cytoskeleton Flashcards
Which of the cytoskeletal structures are made up of protein subunits that are fibrous?
intermediate filaments
In terms of structure, if cytoplasmic intermediate filaments are described as ropes, nuclear lamins could be best described as
mesh
Which of the following represents the placement of microtubules in an epithelial cell?
B (spider)
Microtubules are made up of 13 ___________ that are linear chains of ___________.
protofilaments; tubulin dimers
The end of the microtubule that has /alpha-tubulin exposed is the
(-) end.
Which of the following statements about the cytoskeleton is false?
Covalent bonds between protein monomers hold together cytoskeletal filaments.
Intermediate filaments are found mainly in cells that are subject to mechanical stress. Gene mutations that disrupt intermediate filaments cause some rare human genetic diseases. For example, the skin of people with epidermolysis bullosa simplex is very susceptible to mechanical injury; people with this disorder have mutations in their ____genes, which code for the intermediate filament found in epithelial cells. These filaments are usually connected from cell to cell through junctions called _______.
keratin; desmosomes
The main filaments found in muscle cells belong to the ____ family; people with disruptions in these intermediate filaments can have muscular dystrophy. In the nervous system, ___ help strengthen the extremely long extensions often present in nerve cell axons; disruptions in these intermediate filaments can lead to neurodegeneration.
vimentin; neurofilaments
People who carry mutations in the gene for ___, an important protein for cross-linking intermediate filaments, have a disease that combines symptoms of epidermolysis bullosa simplex, muscular dystrophy, and neurodegeneration. HUmans with progeria, a disease that causes premature aging, carry mutations in a nuclear ____.
plectin; lamin
Dynamic instability causes microtubules either to grow or to shrink rapidly. Consider an individual microtubules that is in its shrinking phase. What must happen at the end of the microtubules that is in its shrinking phase?
If enough GTP-loaded subunits are added quickly enough to cover up the GDP-containing tubulin subunits at the end, a new GTP can form and regrowth is favored.
What would happen if only GDP, but no GTP, were present in the solution?
Microtubules would continue to shrink and eventually disappear, because tubulin dimers with GDP have very low affinity for each other.
What would happen if the solution contained an analog of GTP that cannot be hydrolyzed?
Microtubules continue to grow until all free tubulin subunits have been used up
Compared to the normal situation, in which actin monomers carry ATP, what do predict would happen if actin monomers that bind a nonhydrolyzable form of ATP were incorporated into actin filaments?
That means ATP can hydrolyze to ADP. Hence, it would stabilize the interactions between the monomers of a filament, stabilizing the filament and inhibiting depolymerization, resulting in longer actin filaments.
Even though these drugs have opposite effects on actin polymerization, the addition of either of these drugs instantaneously freezes the cell movements that depends on actin filaments. Explain why drugs that have opposite effects on actin filaments can have a similar effect on cell movements.
So these drugs both stop cell movements because actin polymerization and depolymerization are both required for this process.
As cells move forward, the the growth of ____ filaments near the plasma membrane helps push out the membrane. As this occurs, continuous ____ of actin filaments occurs at the actin filaments away from the plasma membrane.
actin; depolymerization
