Cellular movement Flashcards
modul 2
what is cellular movement?
motility and contractility
what does cell motility involve?
- movement of a cell or organism through the environment
- movement of environment past or through a cell
- movement of components in the cell
what does contractility describe?
shortening of muscle cells, is a specialized form of motility
where does motility occur?
at tissue, cellular and sub cellular level
what are the intracellular components move?
micro tubular based motility
microfilament based motility
what is microtubuler based motility?
sliding of MTs in cilia and flagella
mitotic spindles in separation of chromosomes
what do microtubules and microfilaments provide?
provide scaffold for motor proteins that produce motion at then molecular level
what are molecular motors common features?
- couple ATP hydrolysis to change in shape and attachment
- cycles of ATP hydrolysis, ADP release and acquisition of new ATP
- common structure
- can move along cytoskeletal filaments
what are the microtubule based motility proteins?
dynens and kinesins
what are microfilament based motility motor proteins?
myosins
what do Mts provide?
ridged tracts for transport of organelles and vesicles
what is traffic towards the minus end considered?
inbound
what is the traffic towards the plus end considered?
outbound
what do kinesis and dyneins do?
walk along MT and provide force needed for movement
what side of the MT does dyneins go towards?
the minus end
what end of the MT does kinesin go towards?
the plus end
what kinesin only goes to the minus end?
kinesin 14
what is fast axonal transport?
when proteins produced in the cell are transported to nerve endings
what are the 2 parts of fast axonal transport?
- kinesin-1 involved in AYP dependent transport to the plus end (anterograde axonal transport)
- cytoplasmic dynein moves cargo to minus end (retrograde axonal transport)
what do kinesins consist of?
2 dimerized heavy chains and 2 light chains
what does the heavy chain of a kinesin contain?
globular domains, attach to MT
coiled-coil stalk
lever like neck
tail
what does the light chain associate with?
the tail
how do kinesins move along the MTs?
looks like walking
2 globular heads are like feet
what does each kinesin molecule exhibit?
processivity
what is processivity?
can move long distances along MTs before detaching the ADP and get new ATP
where are dyneins found?
found in axonmes and the cytosol
what are cytoplasmic dyneins?
associated with a protein complex called dynactin
what does dynactin do?
help link dyneins to cargo
what are axonemal dyneins?
activate MT sliding in cilia and flagella
what are characteristic of cilia?
2-10um long
occur in large numbers in surface
occur in both unicellular and multicellular eukaryotes
has oarlike pattern of beating generating force
what are characteristics of flagella?
same diameter as cilia, usually longer
one or a few per cell
move with propagated bending motion which generates force
what do cilia and flagella consist of?
axoneme connected to a Basel body
what structure do cilia and flagellas share?
axoneme
what is the axoneme and the Basel body surrounded by?
extension of the cell membrane
what is between the axoneme and the Basel body?
a transition zone
what pattern characteristic does the transition zone take of?
the axoneme
what is the structure of the Basel body?
looks like centriole
nine sets of triplets stricter around the circumference
what is the structure of the axoneme?
9+2 pattern
outer doublets has one complete MT and on incomplete MT
all tubules of centre pair are both complete
what is a 9+2 pattern?
9 outer doublets and 2 MT in the centre (centre pair)
what are primary cilia?
used in sensory structures
what structure do primary cilia have?
9+0 structure (no central pair)
why are primary cilia important in development?
defects in them can result in deafness and lift right asymmetry reversal
what is the tubule structure?
all tubules contain both tubulin and tektin
what is Tektin?
related to intermediate filaments proteins
A and B tubules share wall in which it is major component
what dies each A tubule have a set of?
set of side arms
what do the side arms do that are on the A tubule?
project from each of the outer doubles
what do the side arms on the A tubule consist of?
axonemal dynein
what are axonemal dyneins involved in?
the sliding of MTs against each other
what does the sliding do when the axonemal dyneins are present?
creates bending of the axoneme
what do syneins arm occur in?
occur in pars of one inner arm and one outer arm
what are adjacent doubles less frequent joined by?
interdoublet links
what do interdoublet links do?
limit extent of relative movement of doublets, link to each other by protein called nexin
what are radial spokes?
project inward towards the central pair at regular intervals
what are radial spokes important for?
translating the sliding of MTs into the bending of the axoneme
what are radial spokes secondary to?
the bending of the MT when sliding
what does the doublet sliding in the axoneme cause?
the flagella and cilia to bend
what slide relative to one another when bending occurs?
adjacent outer doublets
what are crosslinks and spokes responsible for?
bending
what do radial and circumferential connections do?
restrain sliding and lead to bending
what causes doublets to slide past each other?
cleavage of nexin linkages and treatment with ATP
when does the axoneme bend?
when linkages are left intact and traced with ATP
what are dynein sidearms responsible for?
doublet sliding
what do dynein arms provide?
driving force for axonemal bending
what does the removal of dynein from isolated axonemes lead to?
leads to loss of capacity for axonemes to beat (reversible effect)
what does intraflagellsr transport adds to?
adds components to growing flagella and cilia
when does intraflagellar transport occur?
when tubulin subunits are shuttled to and from growing flagellum tip by both + and - end motor proteins
where do kiesins move material to in the flagella?
the tip
where do dyneins bring materials in the flagella?
from tip of flagella to the base
what is the ATP-dependent motor superfamily called?
myosins
what do myosin do?
interact with and exert force on actin microfilaments
how many classes of myosin are known?
24
what direction does myosin generally move towards on a microfilament?
towards the plus end
what myosin only moves towards the minus end?
myosin VI
what are the functions of myosin?
muscel contractions
cell movement
endocytosis
vesicle transport
what myosin is best understood?
type 2 myosins
what is the structure of the 2 heavy chains in myosin 2?
gobbler head, hinge region and rodlike tail
what do the globular domains do?
bind to actin and use ATP hydrolysis for energy to move along the actin filament
what is the light chain for on myosin 2?
one is essential light chain and one is regulatory light chain
play role in regulating the ATPase
what are the efficient motor proteins?
myosin 2 and classic kinesin
what are the 2 similarities in myosin 2 and kinesin?
- both have globular domains that walk along protein filaments and use ATP hydrolysis to change shape
- the forces exerted are simular
what makes myosin different from kinesins?
- microfilament motors
- move short distances
- opperate in large arrays (need many myosins to do function)
what is the most familiar example of mechanical work mediated by intracellular filaments?
muscle contractions
what are the 3 muscles that mammals have?
skeletal
cardiac
smooth
what are skeletal muscles responsible for?
voluntary movement
what do skeletal muscles consist of?
parallel muscle fibers joined by tendons to the bone
what are some features of muscle fibres?
each is a long, thin, highly specialized, multinucleate cell
what does each muscle fibre contain?
numerous myofibrils
what are myofibrils?
each divided along its lengths into units called sarcomeres
what do sarcomeres contain?
bundles of thin filaments (actin) and thick filaments (myosin)
what are the 2 types of muscles that are striated?
skeletal muscles and cardiac muscles
what makes muscles striated?
in myofibrils a pattern of alternating dark and light bands
what are the dark bands in striated muscles?
A bands (has both thick and thin filament)
what Is the light bands in striated muscles?
I bands (only actin and z line)
what is the lighter region in the middle of the A band?
H zone (M line runs down the centre)
what does the M line contain?
myomesin
what are myomesin?
a protein that links myosin filaments together
what is in the middle of each I band?
Z line
what does the Z line defines?
define the length of a sarcomere
hat do thick filaments consist of?
hundreds of myosin
how are myosin’s orientated in the thick filament?
in opposite directions in 2 halves of the filament
how are the myosins arranged in the thick filament?
in a staggered fashion
what do the heads of the myosins do?
contact the adjacent thin filaments forming cross-bridges
what does the thine filament contain?
F-actin, tropomyosin and troponin
what does one troponin complex associate with?
tropomyosin
what does each troponin constitute as?
calcium-sensitive switch that activates contractions in striated muscles
how are the actin in thin filaments oriented?
orientated so all the plus ends are anchored at Z lines
what direction does myosin 2 moves towards?
towards the plus end
what happens when myosin 2 moves towards the plus end in striated muscles?
thick filaments move towards the z lines during contraction
what contributes to the architecture of muscle cells?
structural proteins
what are the structural proteins with thin filaments?
alfa actin
Cap Z
Tropomodulin
Nebulin
what is alfa actin?
keeps actin filaments bundled into parallel arrays
what is Cap Z?
maintains the attachment of plus ends of the Z line and caps the actin in the filaments
what is tropoodulin?
binds the minus end of the filaments to maintain stability
what is nebulin?
stabilizes the thin filament organization
what are the structural proteins associated with thick filaments?
myomesin
titin
what is myomesin?
present at the H zoned bundles the myosin molecules
what os titin?
attaches think filaments to Z lines
keeps it in correct position during contraction
what explains muscle contractions?
the sliding filament theory
what is muscle contraction due to?
thin filament sliding past thick filaments
does the length of the thin and thick filaments change?
no
what narrows during a contraction?
the I band
what is the amount of force depended on?
depends on the number of actin binding domains that makes contact with the thin filaments
what powers cross bridge movement?
ATP
what makes the cross bridge?
links btwn F-actin of thin filaments and myosin heads of thick filaments
what is the first step of the contraction cycle?
- in high energy state “cocked” configuration
myosin globular domain contains an ADP and an Pi molecule
what is the second step of the contraction cycle?
myosin in more tightly bound state triggers a conformational change in ,myosin cherry chain
release of Pi
what is the third step of the contraction cycle?
conformational change associated with power stroke, movement causes thick filament to pull against the thin filament
what is the fourth step of the contraction cycle
myosin heavy chain remains attached to thin filament while ADP is released
what is the 5th step in the contraction cycle?
cross bridge dissociation required new ATP binding. causes heavy chain to change conformation, weakens binding to actin and triggers detachment
why is the 6th step in the contraction cycle?
ATP hydrolysis returns the myosin head to the high energy state
what does the regulation of muscle contraction depends on?
calcium
what regulates the ability of myosin binding sites?
tropomyosin and troponin
what are the actin normally blocked by?
tropomyosin
what just tropomyosin do to allow the cross bridge to form?
must move off of the myosin binding sites on the actin
what does low calcium do?
tropomyosin blocks myosin binding sites preventing interaction with myosin
what happens if calcium is high?
calcium binds to TnC causing tropomyosin to shift allowing myosin to bind
what is the role of neurons in the regulation of calcium levels in skeletal muscles?
nerve impulses from motor neurons activate appropriate muscles
when nerve impulses stop, calcium levels declines and muscle relaxes
what is a neuromuscular junction?
where a nerve contracts a muscle cell, conveying a single to contract in the for of an AP
what do the terminals of the neuron in the neuromuscular junction store?
acetylcholine
why is acetylcholine released?
it is released in response to an action potential
what is the motor end plate?
area of muscle cell membrane under the axon terminal where acetylcholine receptors are
what happens when acetylcholine binds to the receptors on the motor w=end plate?
it opens voltage gated channel for inward Na+ flow
what happens when sodium flows into the muscle fibre?
causes depolarization to be transmitted away from the motor end plate (into the fibre)
How does the depolarization spread through the sarcomere?
through the transverse (T) tubule system
what does the T tubule system contact?
the sarcoplasmic reticulum
what does the SR do when the depolarization reaches it?
releases calcium ions and then quickly remove them as needed
what are the 2 elements of the SR?
- medial element
- terminal cisternae
where are terminal cisternae generally found?
near a T tubule forming a structure called a triad
what does the AP activate while it travels down the T tubule?
voltage gated calcium channels
what are the voltage gated calcium channels next to?
ryanodine receptors in the terminal cisternae
what do the ryanodine receptors do?
opens and releases calcium into the sarcoplasm, causing contraction
what needs to happen for a muscle to relax?
calcium levels must decrease
how do the calcium levels decrease for a muscle to relax?
SR has calcium ATPase to pump calcium back into the SR cisternae
what is the actual name for the calcium ATPase?
SERCAs (sarco/endoplasmic reticulum Ca2+ - ATPase
what are cardiac muscles responsible for?
beating of the heart
what does the coordinated contraction of cardiac muscle cells involve?
electrical coupling
what are some characteristics of cardiac muscles?
not multinucleate, joined end to end by intercalated discs
what do the intercalated discs have?
has many gap junctions so waves of depolarization spread easily from one cell to the next
what is the heart controlled by?
pacemaker regain in the heart
how does the pacemaker work?
wave of depolarization initiated by it speaks to the rest of the heart
how do cottage gated calcium channels work in the heart?
releases a small amount of calcium that indirectly leads to a large calcium release from the ryanodine receptors
what are smooth muscles responsible for?
involuntary contractions in various tissues
what are the characteristics of smooth muscle contractions?
relatively slow and greater duration
what are characteristics of smooth muscle cells?
long and thin with pointed ends
no striations
instead of Z lines, has dense bodies
what are dense bodies in smooth muscle cells?
plaque like structures composed of intermediate filaments
allows slow and long contractions
where ar the bundles of actin and myosin bundled to?
at both ends, they are bundled to the dense bodies
how are the contractions of smooth muscle cells regulated?
when Ca2+ increases, a cascade if events take place
what are the events in the regulation of contractions on smooth muscle cells?
1activation of myosin light-chain kinase (MLCK) phosphorylates a regulatory light chain of myosin
2. leads to myosin conformational change, promoting filament assembly
3. activates myosin so that it can interact with actin filaments to undergo the cross bridge cycle
what are the steps of smooth muscle contraction?
- response to signal, EC Ca2+ enters muscle cell
- increase calcium concentrations inside activates protein calmodulin
- resulting calcium calmodulin complex binds to MLCK
- activates MLCK and triggers myosin light chain phosphorylation
how does a smooth muscle relax?
Ca2+ levels fall and MLCK is inactivated
light chain phosphates removes Pi from myosin light chain
what are other actin based motility?
- cell crawling
- amoeboid movement
- cytoplasmic streaming
what do non muscular cells use to crawl over a substrate?
uses lamellipodia and or filopodia
how does lamellipodia work?
cycles of protrusion, attachment, translocation and detachment
what are the 4 events of cell crawling?
- extension of a protrusion
- attachment to substrate
- translocation (generation of tension which pulls cell forwards)
- detachment
what is cell protrusion and retrograde flow in cell crawling?
cells extend protrusions at their fronts other than or leading edge
what is a lamellipodium?
thin sheet of cytoplasm
what is a filopodium?
thin pointed protrusion
what happens during normal retrograde flow?
MF move towards rear of protrusion as it extends
what does retrograde flow result from in cell crawling?
- actin assembly at the growing tip of the protrusion
- reward translocation of filaments towards the base
what is necessary for cell crawling?
attachment or adhesion of cell to substrate
what are the proteins involved in attachment or adhesion in cell crawling?
- integrins on outside of cells attach to ECM proteins
- inside cell integrals are connected to actin filaments via linker proteins
what happens when a cell contracts in cell crawling?
the rear of the cell squeezes the cell body forward and releases the attachments at rear
what are the cell contractions due to in cell crawling?
actin-myosin interactions under control of Rhode Island, activates non muscle myosin 2 at rear of cell
how does movement occur in cell crawling?
new attachments must be balanced by loss of old attachments
how does directional migration occur?
through the formation of protrusions predominantly on one side of a cell
what do diffusible molecules act as?
cues for directional migration
what is it called when a cell moves in response to a chemical gradient?
chemotaxins
what does chemoattractant result in?
dramatic changes in the actin cytoskeletion
what are the receptors for chemoattractants/repellants?
G protein-linked receptors
what is the cycle of amoeboid movement?
- gelation
- solation
what is gelation?
a pseudopodium extends, more material streams forwards - congeals at the tip
what is solation?
at the rear of the cell, cytosol becomes more fluid and streams forwards
what proteins are activated in gelation?
gelsolin
how is gelsolin activated?
by Ca2+ to convert gel into more fluid state
what can streaming occur in amoeboid movement?
as long as the appropriate ions and other factors are present
what is cytoplasmic streaming?
actomyosin-dependent movement of cytoplasm in the cell
what is the process of cytoplasmic streaming called in plants?
cyclosis
what is cyclosis?
dense set of aligned microfilaments found near sites where cylosis occurs
