The cytoskeleton Flashcards by Kayla Stumo

What are the 5 functions that the cytoskeleton performs

Organization of the cytoplasm
Structural support
Transport
Movement
Cellular divisiond

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Different types of proteins are involved in the different what of the cytoskeleton

Functions

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There are three main types of cytoskeletal filaments, what are they?

Intermediate filaments
Microtubule filaments
Actin filaments

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Each type of filament is a polymer of what

protein subunits

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Mutations in filaments result in what

prominent disorders

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The filaments polymerize and depolymerize as needed to perform their functions and these are processes targeted by what

specific chemotherapeutics

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7nm

(actin)

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25nm

(tubulin)

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10nm

(varies)

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Actin filaments (f-actin) are polymers of what

globular actin (g-actin)

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Actin polymerization requires

ATP

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G-actin is polar like tubulin monomers, meaning that f-actin has

plus and minus ends

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F-actin primarily grows at what end

Plus ends

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F-actin interacts with other proteins that modify the actin structure, allowing actin to do what

Perform various functions

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Actin filaments associate with the cell cortex and mediate actions related to what

The cell membrane

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What are the actions that actin filaments mediate

Membrane fusion (microvilli absorption, “hair” cell formation for hearing / balance)
Budding or Cytokinesis
Crawling of the cell
Muscle contractions

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A signal like PDGF triggers a cell to do what

crawl directionally

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Rac/Rap G-proteins are activated near this edge and create what

Create focal contacts, a loose type of cell footing

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Rho/ROCK subfamily G-proteins trigger actin polymerization and creates and triggers what

Creates more firm, focal adhesions
Triggers crawling of the cell along substrate or other cells

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Decreasing PDGF gradient away from the leading edge has multiple effects what are they

PDGF bound to the receptor is internalized behind the leading edge
GAPs become activated, shutting off actin polymerization back where the cell needs to lift up and off its prior contacts

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The head domain of myosin-I interacts with

f-actin

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The tail of myosin-I interacts with some other structures what are they

(a vesicle, a membrane, etc.)

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Myosin “walks” towards what end

The plus end

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If the myosin tail is attached to cargo, the cargo where

Along the actin

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If the myosin tail is attached to the plasma membrane, the membrane moves

along the actin to affect cell shape

Myosin-II is a dimer that forms what

myosin-II filaments

Myosin filaments are made of multiple

dimers

The myosin heads extend from the edges of the

Filaments

The middle of a myosin filament has how many heads

No heads (bare)

Sliding of f-actin across myosin-II is a

muscle contraction

Muscle cells contain bundles of actin and myosin filaments called

Sarcomeres

Plus ends of f-actin in adjacent sarcomeres are connected by

by Z discs / lines

What do T-tubules do

carry the action potential along skeletal muscle cells (after acetylcholine bound to ion-channel coupled receptor) Brings voltage change close enough to internal sarcoplasmic reticulum (SR) membrane (a specialized type of ER providing ions towards sarcomeres)) Triggers opening of Voltage-Gated Ca2+ channels Ca2+ is released from the sarcoplasmic reticulum

What does Tropomyosin do

binds actin (and troponin) and prevents myosin binding WHEN NOT in the presence of calcium Upon activation, the released Ca2+ binds troponin, which moves Tropomysin slightly along the actin filaments This shift allows myosin to bind its sites on actin

With calcium BUT in the absence of ATP, myosin is able to be bound to actin in what conformations

in the “rigor” or “post-power stroke” conformation

ATP binds myosin, causing a

conformation change in myosin

Myosin releases

F-actin

The ATP hydrolyzes to

ADP (very quickly)

ATP hydrolysis causes another conformational change to myosin, causing what conformation

“cocked” conformation

Once in the “cocked” conformation, the myosin head is positioned slightly shifted from its previous spot along actin (the next subunit) and what is released

Pi is released and myosin again binds f-actin tightly at this next actin subunit then ADP is released, and the myosin head returns to the original conformation, generating a power stroke (the “pull”)

Skeletal muscle contraction occurs multiple times and rapidly to

the actin along the myosin

Not all heads are in sync so that subsets of heads bind actin while others are in the process of what

Release

others are in the process of release Muscles can only pull but can do what

you can still resist the force of a load while slowly lengthening a muscle

Separate Ca2+ channels in the SR are continually pumping Ca2+ back into the SR, but will not be able to outcompete what

VG-Ca2+ channels while a contraction signal is sustained

Once the action potential stops, the VG-Ca2+ channels closed and the Ca2+ can now be

be fully pumped back into the SR

Loss of Ca2+ from troponin then causes tropomyosin to roll back over myosin binding sites and prevent

new myosin/actin interactions without a new signal

The lack of interaction between myosin and f-actin causes

f-actin to slide back to the original position

While mid-size in diameter, they are the STRONGEST cytoskeleton filaments

Intermediate filaments

Diseases associated with mutations in different subsets of intermediate filaments include

ALS (Lou Gerhig’s disease) Progeria (very early advanced aging)

Intermiediate filaments

Extend throughout the cell, but anchor in the plasma membrane where the cell connects to other cells

What do Desmosomes do

Desmosomes connect adjacent cells together to provide strength to epithelium

Types of intermediate filaments

Keratin filaments Vimentin filaments Neurofilaments Nuclear lamins

What is keratin

Found in all epithelial cells Distribute stress when skin (or other epithelial layers) are stretched

what is vimentin

Provides support in connective tissues (ligaments and muscles)

what is neurofilaments

Provide strength to neurons, particularly in the axon

What are nuclear lamins

Nuclear filaments (lamins) provide structure to nuclei; degrade and reform during cell division

What are microtubules involved in

Transport within the cell Cell division (Form the mitotic spindle used to separate chromatids) Locomotion (structural component of cilia and flagella)

Microtubules are a polymer of

tubulin proteins

α end referred to as

“minus end"

β referred to as

"plus end"

The ends of a microtubule are called polar because they

are different

Microtubules grow quickly through addition of subunits at what end

the plus end

Protofilaments have what type of structure

(hollow) structure

Microtubules are produced by

microtubule organizing centers (MTOC)

What is a MTOC called in an animal

Called a “centrosome” in animals

What else to MTOC contain

Contain γ-tubulin – where tubule polymerization nucleates (hard to start polymerizing on their own)

Centrosomes contain two

Centrioles

Centriole function in centrosomes during interphase remains unclear, but they are involved in the structure of what

cilia and flagella structure

Centrosomes are not present in

MOST Conifers, Flowering Plants, or Fungi

Microtubules have

dynamic instability which means what they grow and fall apart quickly

Tubules are constantly produced, but if they do not attach to something, what happens

they fall apart

Stabilizing microtubules require what

Requires GTP, which produces a cap at the plus end

If GTP is hydrolyzed before new subunits are added, the cap is lost and what happens to the tubule

It depolymerizes

Motor proteins “walk” along microtubules, requiring what

ATP hydrolysis to propel “heads”

What does Kinesin do

Moves towards the plus end of a microtubule Carriers ER towards the plasma membrane like a net; In neurons moves towards axon terminals

What does Dynein do

Moves towards the minus end of a microtubule Carries Golgi towards nucleus; In neurons moves away from axon terminals

Centrioles associate with cell membranes and form a

Basal body

structure of a basal body

9 triplet array The basal body produces microtubules inside cilia and flagella

Microtubules provide support to cilia and flagella in what type of cells

Eukaryotic

what is the array of microtubules in eukaryotic cells

9 + 2 doublet array

Prokaryotic cells do not have

Cilia

Prokaryotic flagella are the same or different than Eukaryotes

Different