Cytoskeleton I and II (Cell Bio) Flashcards
CYTOSKELETON
The cytoskeleton determines cellular * ? * and * ? *
A detailed network of protein filaments (intermediate, microtubules, actin) that extends throughout the ?.
All three cytoskeleton filament systems must normally function collectively to give a cell its ?, ?, and ability to ?
Importance
Cells need proper ? in space
Need to interact with ?
Need to interact with their ?
apical is the top or bottom part?
CYTOSKELETON
The cytoskeleton determines cellular * ORGANIZATION * and * POLARITY *
A detailed network of protein filaments (intermediate, microtubules, actin) that extends throughout the cytoplasm.
All three cytoskeleton filament systems must normally function collectively to give a cell its strength, shape, and ability to move
Importance
Cells need proper organization in space
Need to interact with each other
Need to interact with their environment
apical is the top PART as seen in pic and basal lamina the bottom part
CYTOSKELETON
Facilitates the existence of special structures:
- ? - cellular membrane protrusion, increase surface area
- ? - special adhesive protein complexes that help maintain mechanical integrity
- ? Junctions - protein complexes that occur at cell-cell junctions
- ? and ? Membranes - Apical (towards the lumen) Basolateral (away from lumen)
The ? that make up the ? of the ? can form polarized and self- organized structures that can be ?, allowing the cell to rapidly modify its ? and ? under different conditions.
CYTOSKELETON
Facilitates the existence of special structures:
- microvilli - cellular membrane protrusion, increase surface area
(prebiotics help increase the microvilli SA)
- desmosomes - special adhesive protein complexes that help maintain mechanical integrity
- adherens Junctions - protein complexes that occur at cell-cell junctions
- apical and basal Membranes - Apical (towards the lumen) Basolateral (away from lumen)
The proteins that make up the filaments of the cytoskeleton can form polarized and self-organized structures that can be highly dynamic, allowing the cell to rapidly modify its structure and function under different conditions.
CYTOSKELETON
THE CYTOSKELETON ENABLES A CELL:
- To organize and maintain its correct ? and ? (external/internal)
- To resist ? deformation
- To stabilize ? and its ? (by associating the cell to other ? and to its surrounding extracellular tissues)
- To change its shape for ? and ?
THREE DIFFERENT TYPES OF FILAMENTS COMPOSE THE CYTOSKELETON:
which are?
CYTOSKELETON
THE CYTOSKELETON ENABLES A CELL:
- To organize and maintain its correct shape and structure (external/internal)
- To resist mechanical deformation
- To stabilize itself and its environment (by associating the cell to other cells and to its surrounding extracellular tissues)
- To change its shape for movement and migration
THREE DIFFERENT TYPES OF FILAMENTS COMPOSE THE CYTOSKELETON:
which are: actin filaments, intermediate filaments, microtubules
(AF and IF responsible for mechanical resistance of cell)
CLASSIFICATION OF CYTOSKELETON COMPONENTS
IMMUNOFLUORESCENCE STAINING DETECTION OF * IMP ? FILAMENTS (MICROFILAMENTS) & *
- immunoflu.. attached to actin filaments
** Actin filaments determine the ? of a cell and are necessary for cell ? **
Microtubules determine the ? of membrane-enclosed organelles, direct ? transport, and form the ? spindle
Intermediate filaments provide ? strength
** Actin filaments determine the shape of a cell and are necessary for cell locomotion **
Microtubules determine the position of membrane-enclosed organelles, direct intracellular transport, and form the mitotic spindle
Intermediate filaments provide mechanical strength
CYTOSKELETON
Actin filaments and microtubules are built from subunits that are ? and ?.
Intermediate filaments are made up of smaller subunits that are ? and ?
All three filaments form ? assemblies of subunits that ?-associate, using a combination of ? and ? protein contacts.
CYTOSKELETON
Actin filaments and microtubules are built from subunits that are compact and globular
Intermediate filaments are made up of smaller subunits that are elongated and fibrous
All three filaments form helical assemblies of subunits that self-associate, using a combination of end-to-end and side-to-side protein contacts.
** MICROFILAMENTS - ACTIN STRUCTURE & FUNCTION **
Found in eukaryote cells, actin performs a ? range of ? in cells
Essential for:
? support
? → cell crawling, engulfing, migrate, muscle movement
Cell ?, ? → microvilli
ACTIN- STRUCTURE & FUNCTION
Form a tough, but flexible framework
-> G-Actin subunits are ? and ?. Form a tight, right-handed helix called filamentous actin (F-actin)
* Actin-Filament (F-Actin) consists of 2 parallel ?
* rigid or flexible? structure
* Usually shorter than ?
** MICROFILAMENTS - ACTIN STRUCTURE & FUNCTION **
Found in eukaryote cells, actin performs a wide range of functions in cells
Essential for:
mechanical support
movements: cell crawling, engulfing, migrate, muscle movement
Cell shape and structure → microvilli
ACTIN- STRUCTURE & FUNCTION
Form a tough, but flexible framework
-> G-Actin subunits (basic parts) are compact and globular. Form a tight, right-handed helix called filamentous actin (F-actin)
* Actin-Filament (F-Actin) consists of 2 parallel protofilaments
* flexible structure
* Usually shorter than microtubules
ACTIN- POLYMERIZATION
Actin filaments can grow by adding more actin monomers at either end (-) or (+):
o Nucleation
o Elongation
o Steady State
Each free actin monomer carries a tightly bound ?
o ATP bound actin has a higher affinity for the ? subunits and remains ? in the filament
o ADP bound actin can ? from the filament
Hydrolysis of ATP->ADP
- Reduces strength of binding b/t monomers
- Decreases polymer ?
Accessory proteins regulate actin ?
? – inhibits nucleation
? – accelerate depolymerization
ACTIN- POLYMERIZATION
Actin filaments can grow by adding more actin monomers at either end (-) or (+):
o Nucleation
o Elongation
o Steady State
Each free actin monomer carries a tightly bound ATP
o ATP bound actin has a higher affinity for the neighbouring subunits and remains stable in the filament
o ADP bound actin can dissociate easily from the filament
Hydrolysis of ATP->ADP
- Reduces strength of binding b/t monomers
- Decreases polymer stability
Accessory proteins regulate actin dynamics
profilin – inhibits nucleation
cofilin – accelerates depolymerization
ACTIN – Polymerization and depolymerization
Actin filaments can polymerize to ? or ?
ATP bound actin has a higher affinity for the ? subunit and remains ? in the filament
? bound actin can more easily dissociate from the filament
ACTIN – STRUCTURE (Cell shape):
?-forming crosslinker: (more ?)
?-forming crosslinker: (?)
Actin filaments exist in different ? in cell
Formation depends on actin ? (actin- binding proteins)
examples of cross-linking proteins
o Fascin: ? bundles
o Filamin: 3D ?-forming networks (At 90 degree angle)
ACTIN – Polymerization and depolymerization
Actin filaments can polymerize to grow or depolymerize (break down into polymers)
ATP bound actin has a higher affinity for the neighbouring subunit and remains stable in the filament
ADP bound actin can more easily dissociate from the filament
ACTIN – STRUCTURE (Cell shape):
bundle-forming crosslinker: (more rigid)
gel-forming crosslinker: (networks)
Actin filaments exist in different spatial arrays in cell
Formation depends on actin crosslinking proteins (actin-binding proteins)
examples of cross-linking proteins
o Fascin: linear bundles
o Filamin: 3D gel-forming networks (At 90-degree angle)
ACTIN – Microvilli support
- Actin filaments are cross-linked by
o ? packed ? arrays - Proteins involved in crosslink:
o are big or small? flexible or rigid?
o Force filaments to align closely Example: ?, fimbrin - Can support the way ? project
- Can also ? (associated with myosin I and calmodulin)
Gel-forming crosslinker
? crosslinked in a 3D-like meshwork with ? gel-like properties
Proteins involved in the network:
o small or large? and rigid or flexible?
o Crosslink more parallel or perpendicular?
o I.e., ?
ACTIN – Microvilli support
- Actin filaments are cross-linked by
o closely packed parallel arrays - Proteins involved in crosslink:
o are small and rigid
o Force filaments to align closely Example: villin, fimbrin - Can support the way microvilli project
- Can also contract (associated with myosin I and calmodulin)
Gel-forming crosslinker
loosely crosslinked in a 3D-like meshwork with semisolid gel-like properties
Proteins involved in the network:
o large and flexible
o Crosslink more perpendicular
o I.e., Filamin
ACTIN – Cell movement
Actin crosslink and cell movement:
stress fiber: ? bundle
cell cortex: ? network
filopodium: ? bundle
stress fiber: contractile bundle
cell cortex: gel-like network
filopodium: tight parallel bundle
ACTIN – Cell movement
Three main processes are known to be essential for movement and all involve ACTIN
- The cell pushes out its protrusion at its ”?” or “? edge”
- These protrusions stick to the ? over which the cell crawls
- The rest of the cell drags itself ? by traction
- IMP Examples of cells that do this:
1. Carnivorous ?
2. ? (WBC)
3. ? axons in response to
growth factors
4. ?
ACTIN – Cell movement
Three main processes are known to be essential for movement and all involve ACTIN
- The cell pushes out its protrusion at its ”front” or “leading edge”
- These protrusions stick to the surface over which the cell crawls
- The rest of the cell drags itself forward by traction
- IMP Examples of cells that do this:
1. Carnivorous amoeba
2. neutrophils (WBC)
3. developing axons in response to
growth factors
4. fibroblasts
ACTIN - CELL DIVISION
CYTOKINESIS:
The part of cell division when the ? cell divides into 2 daughter cells
Following the completion of ? (nuclear division), a ? ring consisting of actin filaments and myosin (II) divides the cell in two:
* Cell membrane will grow inward (cleavage) and ? off
ACTIN - ASSOCIATED PROTEINS → MOTOR PROTEINS
Myosin, Kinesin & Dynein
* ? proteins that cause motion inside ? in association with parts of the ?
* All are ?
* ATP → ? energy (transport, muscle movement, beating of cilia and flagella)
** Actin associates with myosin to form ? structures
All ?-dependent motor proteins belong to the myosin family **
ACTIN - CELL DIVISION
CYTOKINESIS:
The part of cell division when the eukaryotic cell divides into 2 daughter cells
Following the completion of mitosis (nuclear division), a contractile ring consisting of actin filaments and myosin (II) divides the cell in two:
* Cell membrane will grow inward (cleavage) and pinches off
ACTIN - ASSOCIATED PROTEINS → MOTOR PROTEINS
Myosin, Kinesin & Dynein
* Motor proteins that cause motion inside cells in association with parts of the cytoskeleton
* All are ?
* ATP → ? energy (transport, muscle movement, beating of cilia and flagella)
** Actin associates with myosin to form contractile structures
All antin-dependent motor proteins belong to the myosin family (and not to the kinesin and dynein) **
ACTIN – Motor proteins: Myosin family
Myosin I
o #? head and a ?
o ? vesicles (tail can bind to)
Myosin II - MOST COMMON
o #? globular (ATPase) heads and ? tail
o Produces muscle contraction in some or most animal cells?
o In non-muscle cells: contractile ?-stress fibers
Myosin V
o ? transporter (i.e. RNA, Vesicles, Organelles, Mitochondria)
o ? keeping vesicles and organelles in the
?-rich ? of cells
ACTIN – Motor proteins: Myosin family
Myosin I
o 1 head and a tail
o transporting vesicles (tail can bind to)
Myosin II - MOST COMMON
o two globular (ATPase) heads and coiled tail
o Produces muscle contraction in most animal cells
o In non-muscle cells: contractile bundle-stress fibers
Myosin V
o Cargo transporter (i.e. RNA, Vesicles, Organelles, Mitochondria)
o Tether like keeping vesicles and organelles in the actin-rich periphery (outer limits of an area) of cells
ACTIN & MYOSIN IN MUSCLE
?: contractile elements of the muscle cell
- Consists of a chain of tiny identical contractile units called ?
- Sarcomeres- highly organized assembly of 2 types: ? and ?
Actin and Myosin - Muscle contraction
Sarcomeres:
Highly organized assembly of 2 types: actin and myosin II filaments
→it’s a ? unit
Contraction is caused by a * ? * shortening of all the sarcomeres
Caused by * ? * sliding past the myosin filaments
ACTIN & MYOSIN IN MUSCLE
myofibril: contractile elements of the muscle cell
- Consists of a chain of tiny identical contractile units called sarcomeres
- Sarcomeres- highly organized assembly of 2 types: actin and myosin II filaments
Actin and Myosin - Muscle contraction
Sarcomeres:
Highly organized assembly of 2 types: actin and myosin II filaments
→it’s a functional unit
Contraction is caused by a * simultaneous * shortening of all the sarcomeres
Caused by * actin filaments * sliding past the myosin filaments
Muscle contraction
Sliding Filament Model:
A process used by muscles to ?
Myosin ? interact with the actin filaments
The thin (actin) filament slides over the thick filament to cause ?
Depends on sequence of molecular events: ?
Muscle stimulated → ? → ? walks along the ?
This happens over and over again (repeated cycles of attachment and detachment)
THUS, Sarcomere contracts
Muscle contraction
Sliding Filament Model:
A process used by muscles to contract
Myosin heads interact with the actin filaments
The thin (actin) filament slides over the thick filament (myosin) to cause tension
Depends on sequence of molecular events: cross-bridge cycling
Muscle stimulated → contraction → myosin heads walk along the actin filament
This happens over and over again (repeated cycles of attachment and detachment)
THUS, Sarcomere contracts
ACTIN - muscle contraction
- The myosin head has ATPase on it so when ATP binds to myosin head it hydrolyzyes into ADP and Pi
- The phosphorylated myosin head now attaches to thin (actin) filament and a power stroke occurs and ADP and Pi are released
- new ? then attaches to myosin and myosin head detaches
- ? of myosin head occurs
ACTIN - muscle contraction
- The myosin head has ATPase on it so when ATP binds to myosin head it hydrolyzyes into ADP and Pi
- The phosphorylated myosin head now attaches to thin (actin) filament and a power stroke occurs and ADP and Pi are released
- new ATP then attaches to myosin and myosin head detaches
- cocking of myosin head occurs
ASSOCIATION OF TROPOMYOSIN AND TROPONINS WITH ACTIN FILAMENTS – Striated muscle
Tropomyosin binds lengthwise along * ? * filaments and is associated with a complex of three troponins:
* troponin I (TnI) - inhibitory
* troponin C (TnC) - calcium
* troponin T (TnT) - tropomyosin
In the absence of ?, the tropomyosin-troponin complex ? the binding of myosin to actin
Binding of ? to which Tn? moves the complex, freeing the myosin-acting binding site, and allowing ? to proceed
ACTIN AND MYOSIN- MUSCLE CONTRACTION
Signal from the ? system -> Triggers an ?
Then the following steps occur:
1. Electrical impulse → depolarize each
? → sarcoplasmic reticulum (main function is to store ? Ions)
- Release ?
- Ca+ + interacts with → ? complex- ?
ASSOCIATION OF TROPOMYOSIN AND TROPONINS WITH ACTIN FILAMENTS – Striated muscle
Tropomyosin binds lengthwise along * actin * filaments and is associated with a complex of three troponins:
* troponin I (TnI) - inhibitory
* troponin C (TnC) - calcium
* troponin T (TnT) - tropomyosin
In the absence of Ca+, the tropomyosin-troponin complex blocks the binding of myosin to actin
Binding of calcium to which TnC moves the complex, freeing the myosin-acting binding site, and allowing contraction to proceed
ACTIN AND MYOSIN- MUSCLE CONTRACTION
Signal from the nervous system -> Triggers an AP
Then the following steps occur:
1. Electrical impulse → depolarize each
myofibril → sarcoplasmic reticulum (main function is to store calcium Ions)
- Release calcium ions
- Ca+ + interacts with → troponin complex- tropomyosin
Drugs that affect actin filaments and microtubules:
ACTIN-SPECIFIC DRUGS (know that these drugs will affect the cytoskeleton)
Phalloidin: binds and ? filaments
the ones below will have a strong impact on actin filament (shape and func. will be compromised)
Cytochalasin: caps filament plus ends
Swinholide: severs filament
Latrunculin: binds subunits and prevents their polymerization
Chemical compounds that stabilize or destabilize actin filaments are important tools in studies of the filaments’ dynamic ? and ? in cells.
PHALLOIDIN (from mushroom)
It can be used for staining ? filaments
-> Binds to all ? of actin filaments in many
different species of animals and plants (very specific)
-> Binds actin filaments and blocks ?
ALPHA-AMANITIN (not related to cytoskeleton)
The main toxic component of the death cap mushroom
-> inhibits RNA-polymerase II
Drugs that affect actin filaments and microtubules:
ACTIN-SPECIFIC DRUGS (know that these drugs will affect the cytoskeleton)
Phalloidin: binds and stabilizes filaments
the ones below will have a strong impact on actin filament (shape and func. will be compromised)
Cytochalasin: caps filament plus ends
Swinholide: severs filament
Latrunculin: binds subunits and prevents their polymerization
Chemical compounds that stabilize or destabilize actin filaments are important tools in studies of the filaments’ dynamic behavior and function in cells.
PHALLOIDIN (from mushroom)
It can be used for staining actin filaments
-> Binds to all variants of actin filaments in many
different species of animals and plants (very specific)
-> Binds actin filaments and blocks depolymerization
ALPHA-AMANITIN (not related to cytoskeleton)
The main toxic component of the death cap mushroom
-> inhibits RNA-polymerase II
MICROTUBULES
Microtubules are polymers of the protein ?
The tubulin subunit is itself a ? formed from two closely related globular proteins called ?- tubulin and ? (each 445-450 amino acids length)
- Each tubulin has a binding site for one ? molecule:
** IMP the GTP that is bound to ?-tubulin is trapped and is never ? neither ?; **
the GTP in beta-tubulin may be in either the ? or the ? form and is ?
MICROTUBULES
Microtubules are polymers of the protein tubulin
The tubulin subunit is itself a heterodimer formed from two closely related globular proteins called alpha-tubulin and beta-tubulin (each 445-450 amino acids length)
- Each tubulin has a binding site for one GTP molecule:
** IMP the GTP that is bound to alpha-tubulin is trapped and is never hydrolyzed nor exchanged **
the GTP in beta-tubulin may be in either the GTP or the GDP form and is exchangeable
Microtubules are hollow cylindrical structures built from ?.
Each composed of alpha- beta ? heterodimers (as it has both alpha and beta; its subunit is a microtubule) stacked head to tail and then folded into a ?
MICROTUBULES
How can microtubules grow and shrink?
By a process called ?
Dynamic instability refers to the ? and ? at the ends of a ?.
The microtubule can dynamically switch between ? and ? phases
Microtubules are hollow cylindrical structures built from protofilaments.
Each composed of alpha- beta tubulin heterodimers stacked head to tail and then folded into a tube
MICROTUBULES
How can microtubules grow and shrink?
By a process called “dynamic instability”
Dynamic instability refers to the coexistence of assembly and disassembly at the ends of a microtubule.
The microtubule can dynamically switch between growing and shrinking phases
DYNAMIC INSTABILITY
Dynamics are influenced by the ? and ? of GTP which occurs only within the alpha or beta?-
subunit of the tubulin ?:
- The addition of GTP - containing ?, to the end of a ? causes the end to ?
- If GTP hydrolysis proceeds more rapidly than the addition of new subunits, the microtubule begins to shrink or grow?
DYNAMIC INSTABILITY
Dynamics are influenced by the addition and hydrolysis of GTP which occurs only within the alpha or beta subunits of the tubulin dimer:
- The addition of GTP - containing tubulin, to the end of a protofilament causes the end to grow
- If GTP hydrolysis proceeds more rapidly than the addition of new subunits, the microtubule begins to shrink
MICROTUBULES- MAPs
Microtubule-associated ? (MAPs) move along ? bringing transport vesicles to target organelles in the cell:
- ?, travels (normally) towards (+) end
- ?, travels towards (-) end
ATP hydrolysis occurs in the ?
Generates movement along the microtubule via the microtubule-binding domains
Dynein is composed of two identical ? chains, which make up two large ? head domains, and a variable number of ? and ? chains.
Transport of intracellular cargos towards the + or - end of the microtubule?
Kinesin has a ? structure to dynein.
Transport of a variety of intracellular ?, including vesicles, organelles, protein complexes, and mRNAs toward the microtubule’s (+ or -) end
MICROTUBULES- MAPs
Microtubule-associated proteins (MAPs) move along microtubules bringing transport vesicles to target organelles in the cell:
- Kinesin, travels (normally) towards (+) end
- Dynein, travels towards (-) end
(pic: atp bind to the myosin heads (which are ATPaes) and then they walk on the microtubules
ATP hydrolysis occurs in the globular head domains
Generates movement along the microtubule via the microtubule-binding domains
Dynein is composed of two identical heavy chains, which make up two large globular head domains, and a variable number of intermediate and light chains.
Transport of intracellular cargos towards the (-) end of the microtubule
Kinesin has a similar structure to dynein.
Transport of a variety of intracellular cargoes, including vesicles, organelles, protein complexes, and mRNAs toward the microtubule’s (+) end
MICROTUBULES -MAPs
The selective stabilization of the microtubules can ? a cell
MAPs (microtubule-associated proteins) can move ? and ? within the cell
Cell polarity refers to ? differences in ?, ?, and ? within a cell.
MICROTUBULES
MAPs can move vesicles with ? (melanosomes) in the skin
(melanin: pigment can be of diff. colors so animals that are rlly good at camoflage - have good VARIETY of melanin and melanosomes will be travelling at microtubules (..dimer?)
changes color quickly, so travels REALLY FAST on microtubles (millisenconds))
MICROTUBULES - MTOC
Microtubules originate from a specific cellular location known as ? (short form?)
* In animal cells, the ? is the major MTOC
Centrosome: made up of 2 cylinders called ?
Centrioles - very small cylindrical organelle near the ? in animal cells, occurring in ? and involved in the development of ? fibers in cell division.
(The centrosome is the whole thing and centrioles present in it)
MICROTUBULES -MAPs
The selective stabilization of the microtubules can polarize a cell
MAPs (microtubule-associated proteins) can move organelles and vesicles within the cell
Cell polarity refers to spatial differences in shape, structure, and function within a cell.
MICROTUBULES - MTOC
Microtubules originate from a specific cellular location known as microtubule organizing center (short form = MTOC)
* In animal cells, the centrosome is the major MTOC
Centrosome: made up of 2 cylinders called centrioles
Centrioles - very small cylindrical organelle near the nucleus in animal cells, occurring in pairs and involved in the development of spindle fibers in cell division.
(The centrosome is the whole thing and centrioles present in it)
