Chapter 14 - The Cytoskeleton and Cell Movement

_____________________ polymerize to form filaments with distinct plus and minus ends.

Actin monomers

The _______ end of actin filaments elongates by the addition of ATP-actin monomers.

plus

Am I dying making all these flashcards?

ye

Actin-binding proteins can stablize and organize filaments into ___________ or ____________.

bundles; networks

no seriously i choked on my fkljsing shell noodles

like jfc i eat some soup from a cup and suddenly i need to be put down

Bundles of ___________________ anchor cells at sites of attachment to the ECM.

actin filaments

____________ are also anchored to regions of cell-cell contact.

Actin bundles

______________ are projections of the plasma membrane supported by bundles of actin filaments.

Microvilli

The movement of cells involves __________________of the plasma membrane.

local extensions

Extensions of the plasma membrane are driven by _________________ and _________________ of underlying actin filaments.

branching; polymerization

Why do actin filaments have a distinct polarity?

Actin monomers are asymmetrical and they associate in a head-to-tail fashion. Since all monomers face the same way, it creates a distinct polarity.

Cytochalasin is a drug that binds to the plus end of actin filaments and inhibits their elongation. How would cytochalasin affect treadmilling?

Since filament elongation would be blocked, cytochalasin would lead to depolymerization of treadmilling filaments.

How do the actin-binding proteins that form bundles differ from those that form networks?

Bundling proteins are small proteins that align actin filaments closely with one another. Actin-binding proteins that form networks are large flexible proteins that cross-link perpendicular filaments.

What types of cell adhesions would be affected by siRNA against vinculin? How about siRNA against beta-catenin?

siRNA against vinculin would affect both focal adhesions and adherens junctions, whereas siRNA against beta-cetenin would specifically affect adherens junctions.

What role do actin networks play in microvili?

They anchor the base of microvilli.

How would cytochalasin affect cell locomotion?

Since cell locomotion is driven by actin filament elongation, it would be inhibited bt cytochalasin.

Muscle contraction results from _________ and ___________ filaments sliding past one another.

actin; myosin

______________ is a motor protein powered by hydrolysis of ATP.

Myosin

Distinct types of _____________ transport cargo in nonmuscle cells.

myosin

Microtubules are formed by polymerization of _________ and ___________ tubulin. They are ______________ with distinct ends.

alpha; beta; polar

__________________ can undergo rapid assembly and disassembly.

Microtubules

_________________ allows rapid remodeling of microtubules within cells.

Dynamic instability

Assembly of microtubules is initiated within _______________, with anchor microtubule minus ends.

centrosomes

_________________ of most animal cells contain centrioles.

Centrosomes

The organization of microtubules within cells is regulated by ______________.

MAPs

Why is the dynamic instability of microtubules critical for mitosis?

Dynamic instability of microtubules is responsible for formation of the mitotic spindle.

What is the cellular function of gamma-tubulin?

It associates with other proteins to form the gamma-tubulin ring complex, which functions as a seed for the nucleation of new microtubules.

How would the loss of centrioles affect formation of the mitotic spindle?

The growth of microtubules that form the spindle is initiated in centrioles, although the pericentriolar material rather than the centrioles themselves initiates microtubule growth.

What effect would siRNAagainst MAP2 have on nerve cells? How about on fibroblasts?

siRNA against MAP2 would disrupt microtubules in dendrites. It would not affect microtubules in fibroblasts, since MAP2 is neuron-specific.

How many types of motor proteins are responsible for movement along microtubules?

Two

_______________ move towards the minus end of microtubules.

Dyneins

Most ______________ move towards the plus end of microtubules.

kinesins

Microtubule ________ ends are usually anchored in the centrosome, with _________ ends extending to the cell periphery.

minus; plus

Different members of the kinesin family and cytoplasmic dyneins and transport cargo in __________________ directions through the ____________.

opposite; cytoplasm

__________ cilia act to sense extracellular signals; _________ cilia are responsible for cell movements.

Primary; motile

Cilia are anchored in centrioles known as ____________________.

basal bodies

Movement of cilia is driven by _______________.

microtubule sliding

Why was the isolation of axonemal dynein more straightforward than the isolation of kinesin?

Axonemal dynein was relatively easy to isolate because it is present in large amounts in cilia.

You are studying the transport of secretory vesicles containing insulin along microtubules in cultured pancreatic cells. Which microtubule motor proteins do you think are involved?

The transport vesicles carry insulin toward the cell periphery, so the motor protein involved is expected to be kinesin 1 or other plus-end-directed kinesin family members.

How would a mutation inactivating nexin affect primary cilia? What about motile cilia?

The loss of nexin would abolish the movement of motile cilia. It would not affect primary cilia.

How do microtubule depolymerases contribute to chromosome movement during mitosis?

They shorten the kinetochore microtubules as chromosomes move to the opposite centrosome during anaphase.

Intermediate filaments are composed of several different types of ______________.

protein

Intermediate filaments form dimers, which associate to form ____________, ____________________, and _________________ filaments.

tetrameres; protofilaments; ropelike

In contrast to actin filaments and microtubules, intermediate filaments are ____________.

apolar

Intermediate filaments are required for _________ of cells in tissues but not for many cells in culture.

stability

How do the nuclear lamins differ from cytoplasmic intermediate filaments?

The lamins form a meshwork that underlies the nuclear membrane, rather than forming ropelike filaments.

You introduce a gene encoding a type 1 keratin into fibroblasts. Would this lead to formation of keratin filaments?

The formation of keratin filaments requires the copolymerization of one type 1 and one type 2 keratin, so introduction of a type 1 keratin alone would not lead to filament formation.

Why are intermediate filaments apolar, even though they are assembled from monomers that have distinct ends?

Intermediate filaments are apolar because they are assembled from subunits (tetraments) that are aligned in opposite directions from each other. Thus, the ends of assembled filaments are indistinguishable.

Why are intermediate filaments particularly important in nerve cells?

Intermediate filaments play a major role in supporting the long appendages (axons) of motor neurons.

How would expression of siRNAs targeted against vimentin affect the growth of fibroblasts in culture?

Intermediate filaments are not required for the growth of cells in culture, so siRNA against vimentin would have no effect.