Chapter 9: Cytoskeleton Cell Motility Flashcards
3 main filamentous structures
1) microtubules
2) microfilaments
3) intermediate filaments
microtubules monomers
alpha/beta tubulin dimer
microfilaments monomers
actin
intermdeiate filament monomers
variety of proteins including LAMINS
main functions of the cytoskeleton
1) provide structural support for the cells and organelles
2) serves an internal framework to organize organelles
3) directs cellular locomotion (cilia and flagella)
4) aids in karyokinesis and cytokinesis.
2 ways to study live cell cytoskeleton movement
1) fluorescence speckle microscopy
2) FRAP
____ microscopy can measure the mechnical properties of cytoskeletal elements
atomic force
_____ microscopy allows to detect tha activity of an individual protein in real time
video microscopy
_______ forms mitotic spindles and the core of cilia and flagella
microtubules
a microtubule is composed of 13 ______, and each _____ is made of alternating ______
a microtubule is composed of 13 PROTOFILAMENTS, and each PROTOFILAMENT is made of alternating Alpha/Beta Tubulin dimers
T/F: a microtubule has polarity
true, one end contains a + Beta tubulin and the other end is a - alpha tubulin
polymerization of tubulin/monomers are linked ______, allowing for quick assembly and take down
non covalently
MAPS stand for
microtubule associated proteins
purpose of MAPS, how are they regulated?
attach to the surface of microtubules to increase their stability and promote their assembly. ex MAP2
regulated by phosphorlation of Ser/Tyr/Thr residues
What type of MAP is associated with Alzheimers?
accumulation of phosphorylated TAU map can cause buildup resulting in neurofibrillary plaques
How do microtubules help maintain plant cell shapes?
microtubules congregate around the edges of the cell and also push cellulose forming enzymes near the plasma membrane, allowing them to form a cell wall.
How do microtubules help neurons?
they function in axonal support and play a role in axonal growth during embryogenesis
microtubules can act as ____ for motoproteins that can carry vesicles
they act as tracks
In axonal transport, where does anterograde movement go? retrograde?
anterograde: away from the cell body
retrograde: movement towards the cell body
T/F motor proteins can travel back and forth along the microtubule
false. a motor protein can only move UNIdirectionally. you need separate different types of motor proteins to move vesicles/cargo back and forth
3 main types of microtubules and the type of cytoskeletal element they move on
1) kinesin -MTS
2) dynein- MT
3) Myosin - Actin/microfilament
which motor proteins use the intermediate filmaent?
none. IF’s are predominantly used for nuclear support (made of lamins)
How are motor proteins mechanical changes coupled to chemical changes?
motor proteins need chemical energy to convert to mechanical energy.
1) bind atp to motor protein
2) atp hydrolysis results in power stroke (mechanical)
Kinesin motor proteins is a _____ constructed of 2 identical heavy chains and 2 light chains
tetramer
which part of kinesin is attached to the micro tubule? what is its other functions?
globular head of kinesin is attached to the track. It is also an ATP-ase and generates force to move along the track.
What part of kinesin is where the cargo is held? How does it know to pick up what type of cargo?
cargo is held by the rod like stalk and tail. Type of cargo hauled is dependent on amino acid sequence on the Tail and neck end of Kinesin.
T/F: the amino acid sequence in the head of kinesin is the same for all types of kinesin motor proteins
true. they all have the same head even if they carry different cargo on their tails because they are all bound by the head to the same type of track
Kinesin motor proteins move towards the____ end of the microtubule. this is aka _____
positive, anterograde movement
how does the head of the kinesin motor protein move along the microtubule?
it is attached to a SINGLE protofilament of a microtubule. uses power stroke
speed of kinesin is dependent on _____
concentration of ATP
the method that kinesin moves is often known as _____
hand over hand model. the two heads (heavy chains) take turns alternatingly binding to the MT protofilmanet
processive movement
doesn’t stop or move in a different direction until the cargo reaches the destination. Kinesin and Dynein are processive motor proteins
Type of kinesin protein that is doesn’t move
kinesin 13; it doesn’t move. it’s involved in the depolymerization of microtubules. (depolymerase)
Type of motor protein responsible for the movement of cilia and flagella
cytoplasmic dynein
which portion of dyein contains the microtubule binding sites? which portion acts as the ATP-ase engine?
the dynein stalk is the portion that connects dynein to the MT. the heavy chain heads contain ATPase function and act as an engine
dynein moves to the _____ end of the microtubule track, aka _____ movement
moves to the negative end of the track, aka RETROGRADE transmission
Which portion of dynein holds the cargo?
trick question. Dynein does not hold any cargo directly. The Tail of dynein (light chains) actually attaches to an ADAPTOR protein called DYNACTIN, which then holds the cargo.
3 main roles of dynein
1) position the spindle and move the chromosomes during mitosis
2) position the centrosome and golgi complex to move vesicles and particles through the cytoplasm
3) cilia and flagella movement
MTOC
microtubule organizing centers
Nucleation
process where tubulin dimers polymerize to form initial chains of microtubule
Where is the starting point of nucleation?
at the MTOC. microtubules begin to form at the MTOC
two types of MTOCS
1) centrosome
2) basa body
the centrosome centrioles are surrounded by negatively charged ____-
pericentriolar material.
relative to the microtubule, where would you find the MTOC?
at the negative side of the microtubules, successive microtubule monomer dimers are added to the positive end.
T/F: microtubules stem from the centrioles
false. MTs penetrate and terminate in the pericentriolar material, they do not touch the centriole
structure of a centriol
9 evenly spaced FIBRILS made of 3 microtubules each. 9+3 organization around to form a ring. each tubule is named A, B and C tubule.
Which microtubule of the three microtubules in the 9+3 circulat structure is responsible for giving a centriole the pin wheel appearance?
A tubule is connected to the center of the centriole by a spoke, giving the centriole a characteristic pin-wheel appearance.
which tubulin dimer would be facing the MTOC?
the alpha tubulin dimer. it is the negatively charged dimer.
how does alpha tubulin stabilize and initiate microtubule formation?
alpha tubulin becomes incorporated with another protein to form the ALPHA TURC complex (at the negative/MTOC end). there is an ALPHA TURC complex for each of the 13 protofilaments, forming a heavy ring complex “tubulin ring complex”
Alpha beta tubulin dimers bind onto the 13 ALPHA TURC ring template, growing outwards at the positive end.
what does TURC stand for
tubulin ring complex
Methods you could change the environment to promote microtubule disassembly
1) decrease temperature
2) hydrostatic pressure
3) increase Ca2+ concentrations
4) addition of cholchicine
what attributes to microtubules ability to assemble rapidly?
the dimers are bound together non-covalently, making it easy to take them apart and put them together.
What type of molecule is required for microtubule assembly besides tubulin?
GTP. GTP must be bound to BETA tubulin before it can be incorporated into the growing protofilament chain. incorporation into the chain results in GTP hydrolysis, leaving GDP-tubulin residue IN the microtubule.
After incorporating a tubulin dimer onto a growing MT chain, why must the GDP-tubulin be recharged with GTP? Why does this prevent breakdown?
GDP-tublin needs to be recharged to GTP in order to form a “structural cap” for the microtubule. GDP provides a lot of strained because it is kinked, and if you didn’t have a GTP cap on the growing end of the chain, the GDP tubulins would break down from the chain again.
GTP-tubulin cap is important to maintain the structure of the MT, and fast GTP-hydrolysis is salient to allow for fast dynamic state.
catastrophe in terms of MTs
rapid breakdown via the removal of GDP-tubulin dimers
two ways that the microtubule protofilament strucutre is maintained
1) microtubule associating proteins help stabilize the structure
2) GTP- cap
where would you find microtubules in a plant cell that was in interphase? during Prophase? Metaphase? Telophase?
1) distributed around the cell
2) MTs arranged in a pre-prophase band to mark where cell division will occur
3) MTs rearrange to form mitotic spindle
4) spindles breakdown and MTs are found in phragmoplast, which aids in separation of daughter cells.
Dynamic instability. What end of the microtubules is this propert seen? What protein helps out with dynamic instability? what does dynamic instability allow a cell to do?
Dynamic instabiltiy: the growing and shrinking of microtubules can coexist in the same region of a cell.
this occurs in the POSITIVE end of the microtubules, where dimers are added and taken off.
TIP+ protein binds to the + end of the MT to regulate growth and shrinkage
Dynamic instability allows for rapid exploration of a cell.
Specific organelles with LOW dynamic activity are relatively stable and do not grow
T/F Basal bodies are like centrioles
TRUE. BBs have the same structure as centrioles and can even turn into centrioles if need be
the beating patterns of flagella is dependent on:
the amount of calcium concentration
the core of a flagellas/cilia is ___
axoneme; and array of microtubules that run LONGITUDINALLY through the entire organelle
structure of an axoneme
9+2 arrangement in a circle (unlike the 9+3 arrangement in the centriole). Positive end of axoneme are at the TIP of the flagella and the NEGATIVE end is at the BASAL body.
in an axoneme, the 9 doublets consist of 2 microtubules, the ___ and the ___. What’re the differences between them?
alpha tubule: complete and larger tubule. Dynein is connected to the alpha tubule
beta tubule: smaller tubule. Only has 11 protofilaments instead of 13.
there are 9 doublets that form a circle of the axoneme. what is in the center of an axoneme?
another double with alpha and beta tubules as well.
the center doublet in an axoneme is coated by a _____ and is connected to the peripheral 9 doublets by ______
the center doublet in an axoneme is coated by a CENTRAL SHEATH and is connected to the peripheral 9 doublets by RADIAL SPOKES
how are the peripheral 9 doublets of an axoneme connected to each otehr?
via NEXIN proteins, that form a bridge.
how many dynein proteins are attached to each of the 9 peripheral doublets on an axoneme?
five dynein arms are connected to the A tubule of each axoneme doublet; 3 on the outside of the tubule and 2 on the inside of the tubule.
cilia and flagella stem from the ____ MTOC, which is located on the ____ end of a flagella/cilia
cilia and flagella stem from the BASAL BODY MTOC, which is located on the NEGATIVE end of a flagella/cilia
growth of axoneme occurs at the ____ end of its microtubules to form flagella
axoneme growth occurs on the positive end
the process responsible for assembling and maintaininf flagella. What motor protein is associated with this process to allow for flagellar growth?
intraflagellar transport. IFT proteins are moved by KINESIN 2 motor proteins along protofilaments to the assembly site at the TIP (+) of the growing axoneme, and moved back to the BASAL BODY by DYNEIN
how does dynein help flagella or cilia move? What about nexin?
dynein is connected to the A tubules of an axoneme and moves via ATP hydrolysis and can create a power stroke that would curve the flagella.
Nexin connects the peripheral doublets of the axoneme together and limits how much the doublets can slide past each other.
this is called the sliding microtubule theory
T/F: plant cells have intermediate filaments for structural support
false. Intermediate filaments are only seen in animal cells
T/F; intermediate filaments have a positive and negative end
false. they have no polarity. individual fibrils (tetramers) of the IF have polarity, but they cancel each other out.
main role of intermediate filaments
provide structural support from physical stress on the cell. Ex/ Type 5 lamin, present as part of hte nuclear envelope lining
how are intermediate filaments interconnected to one another?
via cross bridges made out of PLECTIN
T/F: Intermediate filaments are hollow like microtubules
false. they are rod shaped alpha helices.
Keratins
intermediate filaments in the epithelia
Vimentin
IFs in the connective tissue and glial cells
Neurofilaments
IF in nerve cells
Lamns
IFs in all nuclear cells
basic building block of intermediate filaments
rod-like tetramer formed by 2 antiparallel dimers, which is why the polarity cancels out
why does the IF have no polarity?
because the building blocks of intermediate filaments associate into antiparallel tetramers, cancelling out the charges.
T/F: like microtubules, IF need GTP to bind together
false. assembly does not require ATP
which end of IFs does polymerization occur
there are no positive or negative ends on an IF. units of filaments are added in an end-to end fashion. In fact, units can even be added in the middle of the IF.
how are IFs disassembled
via phosphorylation and dephosphorylation of subunits.
What type of cytoskeletal element do plants use as transport tracks?
actin. microfilament
what does actin need to polymerize into a microfilament?
needs ATP.
a single actin subunit is known as ____. polymerization of the units form ____, which is 2 stranded with helical grooves.
a single actin subunit is known as G ACTIN. polymerization of the units form F ACTIN, which is 2 stranded with helical grooves.
T/F: actin has polarity
true. +/- end like microtubules
which end of actin is the positive end? negative?
negative end: POINTED
pos end: BARBED
what protein is actin assembled onto? how is ATP utilized in the process?
Actin is build onto a SEED protein. Actin is an ATPase like microtubule. ATP needs to be bound onto G actin before it can be incorporated (like beta tubulin), and incorporation leads to the hydrolysis of ATP into ADP. There is a build up ADP-actin subunits in the actin chain, like how there is a build of GDP-tubulin subunits in the MT chain
where does polymerization occur when there are HIGH amounts of ATP-actin? Low amounts of ATP actin? Extremely low amounts of ATP actin?
HIGH amounts of ATP-actin: polymerization occurs at both the positive(barb) and negative (point) end of the actin subunits, but the positive end polymerizes way faster than the negative end
Low amounts of ATP actin: polymerization stops at the negative end of actin and continues at the positive end.
Extremely low amounts of ATP actin: actin monomers are taken from the negative end of actin and put on the positive end of actin, resulting in actin staying the same length—> TREADMILLING
Actin steady state
when the net length of filmaent is the same. there is no growth of the actin chain
actin treadmilling
occurs when there is a very low concentration of Atp-G actin. to maintain the length (steady state) of the microfilaments (2 actin helices), actin subunits are taken fro the nregative end of actin and put on the positive end of actin. there is no new growth.
Main motor protein associated with microfilaments
myosin
is myosin an ATpase?
yes, it is how it creates energy for the power stroke
T/F the myosin heads share the same amino acids sequences
true, all myosin heads are atpases but myosin tails may be divergent
2 groups of myosin
1) conventional (type II)
2) unconventional (type 1, 3,4,5)
Conventional myosins can be found in:
muscle tissue. they are the primary motors for muscle contration
which protein is associated with muscle contraction
Myosin 2!!
HOw many chains comprise myosin 2:
6 poly peptide chains:
2 heavy head ATpase chains
2 PAIRS of light chains that are wrapped around the neck of the heavy chains
what structure of the mysoin two allows it to form filaments?
the braided alpha helices that make up the tail (part of the heavy chains)
Filaments are formed in a ______, overlapping of heavy chains in the ____ region of myosin two.
Filaments are formed in a BIPOLAR MANNER, overlapping of heavy chains in the TAIL region of myosin two.
Purpose of filament bi-polarity
allows myosin to pull actin filaments towards each other, like in a muscle cell.
main difference between conventional and unconventional myosin
unconventional myosin only has a single head ( thus only a single helix structure) and cannot form filaments.
purpose of myosin 1
serves as a cross link between actin filaments of the cytoskeleton
myosin5
an unconvenstional myosin that is actually double stranded with two heavy chain heads that moves processively on an actin filament. Like kinesin but is much bigger and can take bigger steps.
the head of myosin 5 is attached to ____, while the tail of myosin five is attached to ______
the head of myosin 5 is attached to the actin filament, while the tail of myosin five is attached to MELANOPHILIN AND RAB27a Adaptor proteins.
T/F: cargo can bind directly to myosin 5
false. they need to get attached via the adaptor proteins such as rab27a or melanophilin
myosin 6
is also a myosin protein transporter but moves in the NEGATIVE direction, unlike myosin 5 which moves in a positive direction.
where in the endomembrane system would you find mysoin 6?
it is involved with bringing clathrin coated vesicles INTO the plasma membrane, and it helps transport uncoated vesicles to the endosome.
a skeletal cell is aka
muscle fiber
why is a muscle fiber/skeletal cell multinucleated?
because one cell is made up of fusion of MYOBLASTS; embryonic pre-muscle cells.
each muscle fiber is made up of _____
myofibrils
each myofibril is made up of linear _____, which give a striated appearance because of the _____
each myofibril is made up of linear SARCOMERE, which give a striated appearance because of the BANDING PATTERNS OF MICROFILAMENTS
the ___ band is thin filaments. what are the thin filaments made of?
I band= thin filaments. mainly made of actin, also made of troponin and tropomyosin
the ___ and ___ bands are thick filaments. what are thick filmanets made of?
the A and H bands are thick filaments. made of mainly myosin with various other proteins
where is the M zone located?
in the middle of the H band in the center of the sarcomere
were is the H band located?
in the center of the A band; thick filaments where there are no myosin heads, only tails.
how is a sarcomere measured?
from one Z band to the next
In the sliding filament model, skeletal muscles operate by shortening. how does each band move?
I band shortens
Z lines come together
A band stays the same length.
H bands (myosin tail regions )decreased in length
which end of the actin filaments are connected to the Z line?
the actin filaments are aligned with each Z line by its positive BARBED end.
tropomyosin is a constituent of the ___ filaments and are located on the _____ of the actin filaments.
tropomyosin is a constituent of the THIN filaments and are located on the GROOVES of the actin filaments.
____ is a protein that is also present in muscle fibers. they extend from the M line to the Z line but are not apart of the thin or thick filaments. what is the purpose of this protein?
Titin. Responsible for acting as a molecular spring to prvent muscles from being pulled apart when being stretched. It also maintains the myosin filament structure and keeps it in the middle.
Is muscle myosin processive in their movements?
no
during a muscle contraction, the muscle heads bend, and ____ filaments slide over the ____ filaments.
during a muscle contraction, the muscle heads bend, and THIN filaments slide over the THICK filaments.
during muscle contraction. the elongated myosin II neck acts as a ____ allowing the actin filament to slide a greater distance
acts as a lever arm
length of a myosin II (muscle myosin) power stroke is proportional to _____
the length of the myosin neck
purpose of the two light chains that are wrapped around the heavy chain neck of myosin II
to provide more rigidity to the neck.
steps of the energetics of filament sliding
1) the myosin starts already bound to actin. ATP is bound to myosin and the head is released from actin.
2) ATP is hydrolyzed, causing myosin to bind weakly to the actin
3) Pi is released from the myosin head, causing the myosin to bind tighter to the actin filament, triggering a power stroke, where the thin filament moves towards the center of the sarcomere.
5) release of ADP is followed by the binding of a new ATP, starting the cycle again.
How does rigor mortis occur?
stiffness in muscles after death caused by the inability of myosin to detach from the actin because there is no ATP.
sarcoplasm
cytoplasm of a muscle cell
sarcolemme
plasma membrane in muscle cell
sarcoplasmic reticulum
ER in muscle cells (SR)
T Tubules
invaginations of the sarcolemma that extend into the cytoplasm, allowing for NERVE IMPULSE propagation to terminate close to the SR, where the Ca2+ ions are stored.
Neuromuscular junction
contact between nerve and muscle fibers. muscle fibers are organized into groups of motor units; allows for joint innervation
muscle fibers are organized into groups of _____ allows for ______ at a neuromuscular junction
muscle fibers are organized into groups of MOTOR UNITS allows for JOINT INNERVaTION at a neuromuscular junction
Excitation-contraction coupling:
the linking of nerve impulse to the shortening of a sarcomere
process of excitation contration coupling
- motor neuron impuse carried along the interior of the fiber to the transverse tubules, to the SR.
- Ca2+ gates in the SR open, releasing Ca2+ into the cytosol.
- when cytosolic Ca2+ increases, Ca2+ binds to the troponin on the thin filament and triggers troponin to move near tropomyosin
- tropomyson is activated and exposes the myosin binding sites on actin molecules, allowing the ADP-myosin heads to attach to the thin filament, whre filament sliding takes place.
5 Ion channels that are needed to facilitate muscle contraction
1) voltage gated Ca2+ channels on the motor neuron
- action potential opens up these channels and triggers the exocytosis of ACh vessicles into the neuromuscular juntion
2) Ach gated cation channel
- Ach binds to the receptors on a muscle cell, and sodium ions flow into the muscle cell
3) Voltage gated Na+ channel
- Na+ ions flow in due to the Ach channel and excites the cell, making it open ANOTHER Na+ channel due to increasing charge,resulting in further depolarization
4) voltage gated Ca2+ channel on Muscle cell
- influx of Na+ triggers positive depolarization, causing the opening of voltage gated calcium channels. Ca2+ enters the muscle cell from the extracellular space.
5) Calcium-gated calcium receptors
- located on the smooth endoplasmic reticulum, activated by Ca2+ in the cytosol, which opens up the ca2+ channels in the SER. (ex/ Rynodine channels).
- Even more Ca2+ rushes out of the SR, and now Ca2+ can bind to troponin on the actin filaments, triggering excitation-contraction coupling.
What are integrins? what type of cytoskeleton component does it work with to enhance cell motility?
Integrins: TRANSMEMBRANE PROTEINS in the plasma membrane that interacts with ACTIN microfilaments inside the cell.
responsible for anchoring cells to a specific spot on the basal membrane. without integrins, the cells would freely float.
usually, intagrins are located in the ____ of a cell
lamellipodium, extensions of a cell that adheres to the substrate and provides temporary anchorage via integrins for the cell to crawl
