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MCBG EXAM 3 FINAL > 9-5 Cytoskeleton > Flashcards

Flashcards in 9-5 Cytoskeleton Deck (52):

What are the sizes of Actin Filaments

2)These are sometimes called what and where are they usually located?

5-9 nm
2)AKA "microfilaments"-->usually located under the Plasma membrane as Cortical Actin


Size of Microtubules?

25 nm


What is the size of Intermediate Filaments?
2)What are these primarily used for?

10 nm
2)IF are known for their "physical strength" and are used mechanically often


What Filaments are the Cytoskeleton system composed of?

-Highly regulated and dynamic Actin, Microtubules and Intermediate Filaments


What are the 6 Jobs of ACtin (AKA _____)

1. MAJOR: MUSCLE CONTRACTION (light bands are made of Actin)
2. Cell Migration/Movement with lamellipodium foot
3. Cell Adhesion [Adherens junction vs. Focal Contact]
4. Polarization cell-to-cell
5. Phagocytosis


Explain why Actin is involved with cell Polarization

epithelial cells are polarized within due to Actin anchorage between apical and basolateral membrane compartments


Which filament mediates Phagosome capabilities during Phagocytosis?



What is the process of Cell migration/movement using the ____filament? [2]
B: What r the 3 big uses of this movement?

ACTIN FILAMENTS enable cell migration
*cell polymerizes Actin to the PLUS + end and lamellipodium/cell foot protrudes forward---> foot attaches with focal contact Actin adhesion.
2)there is then contraction on the myosin II end and cell moves forward along substratum

B: Development / Wound Healing / Cancer Metastasis


*Actin Filaments have ___subunits assembled in a highly ___process.
*Explain What Actin Monomers look like and how they're related to F-actin?

*Actin Filaments have SOLUBLE subunits assembled in highly regulated process.
*Actn monomer= Globular Actin (G-actin) tht binds to cytoplasmic ATP when free floating.

*Asymmetrical polarized Globular actin (in ATP form) assemble head to tail --forms--> protofilament...2 of these protofilaments wrap around each other--forms--->twisted double helix F-ACTIN FILAMENT


What is the "Ant-Trail" Analogy?

B: why is this important to the overall cell?

Filament stick DISassembly into soluble monomers at 1 place and Reassembly of those monomers into a Filament stick in new place
-->looks like moving "ant trail"

B: ULTIMATELY ALLOWS CELL to repolarmerize filaments to diff areas of the cell"such as the lamellipodium foot -->Cell movement!


1)Explain the "lag" / rate determining step of ACtin polymerization?

2)What does the cell do to address this problem?

1) There is INITIAL lag for oligomers to bind free Actin soluble monomer subunits into a filament stick via polymerization= rate limiting step

2)Cell overcomes by using
Actin Related Protein Complex(ARP or Nuclei) to mimic oligomers and INSTANTLY start Actin polymerization when/where ever you want


Why is there never NO actual NET change in LENGTH of F-Actin filament sticks?

Filament sticks eventually reach EQUILIBRIUM with the concentration of free soluble actin monomers (= Critical Concentration) and is constantly assembling [on +end] and disassembling[- end] together at same time (treadmilling)


Critical Concentration
2)What happens if you go below the CC?

the concentration of free Actin soluble monomer subunits at which Filament sticks have stopped growing in length and are at equilibrium!
**Different for each filament**

2)Going below the CC = SHRINKAGE of the Filament Stick


ARP (___ ____ _______) AKA [ __] allows the cell to....
2) Where can it do this?

ARP2 and 3 (ACtin Related ProteinComplex / Nuclei) allows cell to bypass initial polymerization "lag" and start when/where it wants

2) usually activates Actin polymerization at CELL SURFACE but can do it anywhere in cell!


How does [+] and [-] polarization play a role in Actin polymerization?
2) What is CapZ?

3)WHat is Cofilin?

Actin polymerization occurs on F-actin [+] end since it is more dynamic AND since [ - ]is more sluggish with higher critcal concentration

2) CapZ caps [+] end of actin filament and prevents premature shrinkage

3)destabilize the [-] GDP end and induces DEpolymerization. Monomers released are RECYCLED on the + end during treadmilling.


What's the "alternative"/2nd way to carry out Actin polymerization?

Thymosin[- end] and Profilin [+ end] binds to free subunits monomers and also carry out F-actin polymerization but this process is LESS EFFICIENT


Which end of F-actin filament has higher Critical Concentration THRESHOLD and why?

2)Why is this even important?

[- end] of F-actin filament has "slightly" HIGHER Critcal concentration THRESHOLD-->means it takes more free actin monomers (than what's actually present) to reach CC for the [- end]----leads to--> [-] end shrinkage/disassembly becuz it won't reach CC as fast as +

2)THIS IS WHY YOU HAVE TREADMILLING (+ end assembly and [-] end disassembly)


WHat is the Gel-Actin in the Lamellipodia cell foot?

multiple F-actin filament sticks "gel'd" togethr by either
ARP2/3 or [Filament-binding-complexes] (like Filamen dimer) binding the sticks in different angles to form a GEL


What is Fimbrin?
2) why is this a disadvantage for motor proteins?
3)What is an example of this?

Monomer w/2 Actin binding domains RIGHT next to each other in same direction/orientation = VERY CLOSE TIGHT PARALLEL BUNDLE

2)Motor proteins like Myosin CAN'T get in becuz it's too tight!

ex. Microvilli, Filopodium


1) A-Actinin/contractile bundles

3)How is this related to myosin?

Dimer that spaces out F-actin filament binding domains AND orients them in OPPOSITE directions of one another=ANTIPARALLEL--> (contractile bundle)

2) Found in Stress Fibers(which crosses cytoplasm and surface area) AND MUSCLES

3)space is needed so motor proteins like myosin can move along the spaced out F-actin filament sticks


Terminal Web

Location where [actin gel-arrays] join w/cortical actin under PM and help anchor membrane protrusion into the cell

(how microvilli is planted into the cell)


How does Actin-based drugs work?
2)What is an example of this drug and does it have a positive usage?

TOXIC drugs bind to F- filaments in multiple places and STABILIZE
F-ACTIN FILAMENT STICKS-->disrupts normal polymerization!

(ex. Phalloidin from the DEATH CAP MUSHROOM)
-also are powerful tools in lab to stain and understand ] Actin
--->reduces the Critical Concentration threshold to zero! -->Actin will always keep growing and growing and growing at ANY free actin monomer concentration


Global Actin Rearrangement includes these. Describe:
1) Rho - GTPase

2)Rac Rho
3) Cdc42 Rho

1) fibrin biochemical switch that creates AnTi-Parallel Actin stress Fiber organization in active (GTP form)

2)GTPase that creates Lamellipodia/Membrane Ruffles or "curtains" and is often seen a lot in migrating cells

3)makes TIGHT Parallel bundles of ACtin like Filopodia or MICROSPIKES


How do Bacterial toxins target actin polymerization?

disrupt actin polymerization by messing with Rho GTPase Family---->
-cell death
-tight junction problems/diarrhea
-DEC in cell integrity


What happens if you INC the free actin monomer concentration ABOVE the critical concentration threshold?

The F-filament stick will began to grow!


What does Phalloidin drug do when you DEC free actin monomer subunits to low low number?

Even if you dilute out all the free actin monomer subunits to low # the F-actin filament stick IS STILL STABILIZD[Critcal concentration threshold=0] due to Phalloidin and WONT DISASSEMBLE like normal F-actin would


Describe Myosin II

Myosin II dimer motor protein
(2 Long coiled helix tails with N-terminal power head)
*a-helix tails overlap in the bear zone and ultimately form bipolar (head pointing in diff directions) THICK Filament

*Move toward the + end (more common) or move toward [-] end


how do you get muscle contraction?

ATP DEtaches myosin bipolar THICK heads from ACtin and then ATP hydrolysis causes myosin 2 "cock back"
---(Phophate release)-->myosin rebinds stronger to actin
----ADP release--->power stroke moving multiple actin toward [+ end] of other opposite pointed actin!=Rigorous state

These myosin bipolar thick heads work rapidly and independently!


Rigorous State
2) How is ATP related to the Rigorous state and muscle contrction?

Rigorous=ATP is ABSENT and all myosin heads are bound to Actin thin filament contracted


Familial Hypertrophic Cardiomyopathy

Myosin Beta heavy chain mutations can cause Enlarged Heart, Cardiac arrhythmia and Sudden Death of young athletes!


2)What are 5 big functions?

can be near nucleus (Microtuble organizing centers)
1. positioning organelles
2. cell anaphase division [mitotic spindles]
3. enable inner cell vesicle movement (from ER->Golgi, etc. )
4. Cell motility [sperm,protozoa via flagella]
5. Cilia in respiratory tract

(ex. Golgi kept near Nucleus)


Describe the structure of Microtubules

1. soluble subunits are a-tubulin and b-tubulin dimers binds to GTP
2. 13 protofilaments in a hollow straw "slurpy straw"
3. Rigid and highly polar
4. [-] end burried in microtubule organizing center(centrosome most common) STABILIZES IT and so this is why no addition or subtraction going on at the [- end]


Microtubule Organizing Center

in centrosome there are gamma-tubulin ring complexes (similar to ARP2/3 or nuclei of the Actin filaments)that ultimately pushes centrosome toward center of cell near nucleus because it polymerizes microtubules in a spherical pattern outward. [-] ends are burried within.


1) What happens if you hydrolyze the GTP cap on microtubules?
2) How does the cell "Rescue" this?
3) Why doesn't this affect the [-] end of microtubules?

hydrolyzing [+ end] GTP cap (mistakenly happens over time)-->
GDP tubulin dimers alone --(changes)-->normally stable microtubule subunit
into a CATASTROPHE! with rapid depolymerization @ the [+ end]

2)GTP bound subunits will add on to subunits and have growth which will lead to growth and shrinkage back-and-forth over time=Dynamic Instability

3) won't affect [-] end because it is protected within the centrosome sphere


MAPs? [ 2functions]
2) How is tau related to Alzheimers Dz?

A. Give spacing between microtubules
[BIGGR SPACED MAP2 vs. shrtr tau]
B. Stabilize microtubules

2) tau MAP protein when hyperphosphorylated--(leads to)--> Neurofibrillary Tangles--(causes)-->Alzheimers Dz [neuron death]


Is shutting off Dynamic Instability ok?

NO! Interfering with Microtubule Dynamic Instability (ability of filament to grow and shrink) is BAD! it needs this!


What is the negative side of using Microtubule-targeted cancer drugs?

it targets ANY rapidly proliferating cell using microtubules to grow (skin, hair) and has many side effects

-they are MORE clinically used than actin drugs though
Ex. Taxol = stabilizes microtubules and prevents mitosis


1)Kinesins vs. Dyenin?
2) What is axonemal dyenin?

Kinesis move stuff toward the + end of microtubules-->involved in carrying out ER--->X transport

Dyenins retrograde move toward [-] end microtubules
[axonemal dyenin move specifically in cilia and flagella]


How is microTUBULE motor movement diff. than microfilament?

MCT dimers have Each bipolar head in contact with the ACtin filament 50% of the time [not rapid or independent] and work with each other = SLOWER but more stable long-acting movement-->HIGH PROCESSISIVITY


What is the internal structure of Flagella & Cilia [2]

Cilia and Flagella have axonemal dyenin
1 WHOLE dublet with 9 Microtubule Dublets inside each surrounded by 2 microtubule singlets

2)FLagella=SPerm and PRotozoa=WAVE-LIKE MOTION
Cilia= Respiratory Epithelium= whip-like motion


Basal Body structure [purpose and structure]
2) where is this typically located?

Anchors Flagella and cilia into cytoplasm and consist of 9 microtubule triplets with no center pair of singlets microtubule (VERY similar to what is in a centriole of a centrosome)


Kartagener's Syndrome

defect in ciliary dyenin motor protein RESPONSIBLE FOR cilia and flagella to move
2) Male sterility and Respiratory infections


Intermediate Filaments (AKA ___ filaments)
2) where are they common

Intermediate Filaments (AKA Kerotinocytes)= Express a lot of Keratin and important for giving mechanical strength to cells. Are abundant in tissue tht withstand a lot of physical beat down (heart, muscles, skin)
1. Cell strength
2. cell-to-cell adhesion brtween cytoskeleton and adjacent cells via desmosomes that connect them


Neurofilaments purpose and it's relation to ALS?

Intermediate Filament tht Determines Axon diameter and if unregulated can become clustered in brain-->Leu Garrets dz / ALS [ Amyotropic Lateral Sclerosis]


Nuclear Lamina

Beneath nuclear envelope, this intermediate filament structure gives nucleus its shape


What are some KEY characteristics to note regarding Intermediate Filaments? [4]

1. 2 dimers of bipair coiled protofilaments come together in an anti-parallel fashion to make SYMMETRICAL soluble tetramer subunit.
2. Non-Polar Filament! [very diff from the other filaments!]
3. VERY strong structure
4. Very Heterogenous [HUGE gene family-DIVERSITY w/TISSUE SPECIFIC expression]


2. Where could this be found?
3. What helps it

Bundle of cytokertain Intermediate Filaments tht interact at
C-terminal domains with each other
2. Skin
3. Plectin and Filaggrin[Filament Aggregation] accessory proteins bind to this bundle


1. Musculary Dystrophy with Epidermolysis Bullosa Symplex Cause?
2. What is Plectin?
3. [ 3] associated sx?

Caused by Dz in Plectin [universal linker dimer connecting
Vilmentin IF, Actin &Microtubules --> maintains mechanical cell integrity] .

-EBS (blistering dz due to defect in Intermediate Filaments)
-Neurodegeneration (defect in neurofilaments)
-Muscular Dystrophy (defect in Desmin)
Pt have ALL 3 SX!


What are the 4 TYPES of Intermediate Filaments being that IF is extremely _____ (list Name, polypeptide and cell location)

Intermediate Filaments are HETEROGENOUS(Huge Gene diversity)!
1. Nuclear=Lamins/Nuclear Lamina--if DFcT--->Progeria

2. Vimentin-like= Desmin/Vimentin--loctd in->muscle and glial cells
3. Epithelial= Kertain IF--loctd in--> hair, nail and epithelial
4. Axonal=Neurofilament--loctd in--> Neurons


How can we Use Intermediate Filaments to determine origin of cancer?

Intermediate Filaments gene DNA is soo specific to a specific tissue that if cancer cell metastasized/transloctd and you stain for the IF in it you will know where it came from




Intermediate filaments used in Cell-Cell Adhesion

2)HEMI-desmosomes=Cell-MATRIX Adhesion


Flagella & Cilia both have ____singlets surrounded by ___ doublets.
2) These two connect to a cell body via the [basal body] which itself is made of ___ ______

Flagella & Cilia both have 2 singlets that are SURROUNDED by 9 doublets.
2)They connect to cell body via [basal body] which itself is made of 9 TRIPLETS! smh