Cytoskeleton Flashcards
cytoskeleton
- Fibrous proteins found in cytoplasm, not in the nucleus
- 3 parts
1. Intermediate filament (10 nm)
2. Microtubules (25 nm) (b/c there is a hole in the center)
3. Actin filaments (7 nm)
Immunofluorescence
- technique for visualizing the cytoskeletal elements
- antibody to a specific protein target
antibody
- protein (dimer) shape of a Y, at the two top branches–> areas called antibody (Ab)
- specific binding site for antigen (target)
- part of immune system
- ex. isolate intermediate filaments- isolate major component and inject into mouse, inject into rabbit–> rabbit will have immune response to the protein; recognize it as a foreign protein
–> rabbit will start making these kinds of antibodies (millions) so in the future, they will stick to it and kill it off
Intermediate filaments
- shape & strength of cell- anchor and keep cell in place
- intermediate filaments assemble on top of each other, twisted together
- also part of the junction in epithelial cell
- ex. keratin in skin, neurofilaments in neurons, Nuclear lamin in nuclear envelope
Microtubules
- tube w/ lumen, 13 rows of filament
- made up of tubulin dimers (protein)- 3-D shape, tertiary structure
- quaternary- alpha and beta tubulin assemble to create dimers=microtubule subunit
- Dimers are assembled at one end and form tube spontaneously
- line of tubulins= protofilament (don’t assemble in line)- always 13
- (+ and - end)- alpha (-) end assembles slower than beta (+) end
Microtubule locations
- interphase cell- when not dividing- scattered throughout the cytoplasm they emanate out from centrosome
- -> MTOC (microtubule organizing center/call center) - dividing cell- mitosis- Two cell centers and microtubules are emanating out and hold onto chromosomes to pull to opposite poles
- Ciliated Cell- cilium help things beat to move past the cell/swim
- Flagellated Cell- only sperm cell
Centrosome
area near nucleus with emanating microtubules
centrosome always has a pair of centrioles (short/barrel like, right angles) at the cell center
–>9 groups of the 3 microtubules
–> arrangement is referred to as 9 + 3
–> in centriole and basal body, it is 9+0
Cilia and flagella
- work in the same way have beating motion
only in Eukaryotes–> different from in prokaryotes/bacteria where motion is rotary - both 9+2 arrangement
tubulin
protein made up of 100+ amino acids
2 types- alpha and beta
centriole
- always occur in pair- 2 centrioles at the cell center
- made of 3 microtubules fused together and then there are groups of those fused microtubules
- Always 9 groups of 3 microtubules
open space in the middle–> 9+0 - do not have dynamic instability
dynamic instability
- at ay particular moment for any particular microtubule, it may be elongating or shrinking
to establish the cell shape that it wants and to move things around in the cell - Ends- plus (grows longer faster), minus (grows slowly)
GTP
energy molecule- gunaosine triphosphate
- microtubule dimer binds with GTP molecule, GTP increases tendency to assemble dimers
- As the GTP sits around, it hydrolyses so the GTP gets broken by the tubulin molecule and becomes GDP + a free phosphate (Pi)
- once Pi is released, GDP has a tendency to disassemble
inorganic phosphate
free phosphate (Pi) from hydrolysis of GTP--> GDP + Pi
GDP Gap
when GTP bound to tubulin dimers, assembly is faster than hydrolysis –> have a GDP cap
If the process slows and goes in reverse (bc of dynamic
instability), we have paused, and a short amount of time has passed and GTP’s hydrolyze and then GDPs form and everything shrinks.
Pi comes off of GTP and it floats away in aqueous medium –> left with GDP
cilia and flagella
cilia- short and beat (don’t rotate), many (50+), on lung cells (beat out mucus to trachea–> clear throat), all over paramecium, lung infection can kill epithelial cells–> cough after because forming new epithelial cells
flagella- only on sperm in humans, organisms only have 1-3, long and thin
microtubule motors
- mechanism behind bending/beating
- each pair of MTs have one pair of motors that reach out and grab onto the next pair and try to walk along it
- when ATP present, causes motor to walk along and push other side down so it moves up (motors walk towards (-) end)
- microtubules are held together –> causes bending instead of sliding
Axoneme
- complex internal structural components of a flagellum or
cilium (not including the membrane)
basal body
- at the bottom of every flagellum or centriole
- centriole that is now being used as an anchor for the base of a flagellum or cillium
internal spokes
- connecting proteins inside the MT
- causes bending when MT begins to walk along another
bending action
With ATP:
dynein motor causes MT to slide in isolated doublet
dynein motor causes MT to bend when proteins are linked (flagella)
dunein have motor like feet
Neuron MT
-when NTs are ready to be delivered to axon
–> NT packed in cell body in a vesicle, placed on track, motor walks them down and sticks onto microtubule and moves down
– Membranes are recycled from axon and brought back to cell body
BIdirectional transport
–> Dynein motor carries things back to cell body (from + to -)
–> Kinesin motor carries things (vesicles) towards the axon (from – to +)
motor protein (dynein and kinesin)
- MT motor attaches to ATP
- hydrolysis ATP to ADP and phosphate
- back end moves, puts its foot down again, and then releases ADP–> causes front foot to pick up and now it’s back at starting condition
- As long as there are ATPs, there are feet to keep moving, which causes motor to walk along the microtubule
next
actin filament function (globular actin/g actin)
make actin, assembles into a higher order fiber
- an epithelial cell with a bunch of folds that increase areas of absorption in the gut (microvilli supported by actin)
- anchor cell into substrate and it runs actin filaments in between adhesion spots
- crawls along substrate- actin filaments depolymerize into g-actin–> increases the # of particles, water of the cell moves toward the bottom of the cell, cell will move in that direction because of osmosis
- dividing cell, we have microtubules separating chromosomes–> actin wraps around cell and pinches it
Filamentous actin
Take individual globular actins and bind it to itself to make a long strand and TWO strands wind up together
Microvilli
All of things on the side supporting fingers are actin
filaments
actin treadmilling
- different than dynamic instability
- can assemble or disassemble at either end
- adding on one end, falling off the other end at the same rate, length doesn’t change
- ATP assembles, ADP disassembles
capping actin filaments
- some drugs, like cytochalasin, cap the actin filaments and prevent them from elongating
- can prevent the growth of cancerous cells
extracellular matrix (ECM)
ECM secreted by the cell
• help cells anchor in place
• Connect with other cells
• Create an environment that the cells like to live in
• Long firs, like proteoglycan and collagen (protein structures secreted outside the cell)
• transmembrane proteins- anchor outside fiber network to inside fiber network
desmosome
- holds cells together
- intermediate filament attaches to desmosome
chemotherapy drugs
- target cell division
- can upset stomach and hair growth because lots of cell division there
- preventing tubulin polymerization
fibrous structures
- elastin- allows skin to stretch
- collagen- resists stretch
- extracellular matrix- where fibers are found
- integrin- holds together fibers
