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
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
COLCHICINE
- Alkaloid of the autumn crocus (Colchicum autumnale)
- binds free tubulin -> prevents ? and ?
- anti- ? effects
INTERMEDIATE FILAMENTS
* No ? → so no ? or ? end
* Subunits don’t contain ? or ?
* Not involved in ?
* No ? associated
However… ? are associated with ? junctions, ? cells and epithelia, tissue ? stability
MICROTUBULES
COLCHICINE
- Alkaloid of the autumn crocus (Colchicum autumnale)
- binds free tubulin -> prevents MT polymerization and cell division
- anti-inflammatory effects
INTERMEDIATE FILAMENTS
* No polarity → so no + or - end
* Subunits don’t contain ATP or GTP
* Not involved in cell movement
* No motor proteins associated
However… intermediate filaments are associated with cell-cell junctions, strengthening cells and epithelia, tissue mechanical stability
Intermediate filaments
In diseases where the gene coding for keratin is ?, the final protein disrupts the normal ? network in the ? cells of the skin and the epidermis can easily be detached (blistering)
* E.g. epidermolysis bullosa simplex (EBS)
INTERMEDIATE FILAMENTS
Other intermediate filaments
?: high concentrations along the axons of vertebrate neurons
* Participate in axonal growth (length and diameter)
* Provide strength and stability to the axon
?: mechanical stability of cell nucleus
?: scaffold function for sarcomere (skeletal and cardiac muscle)
Intermediate filaments
In diseases where the gene coding for keratin is mutated, the final protein disrupts the normal keratin network in the basal cells of the skin and the epidermis can easily be detached (blistering)
* E.g. epidermolysis bullosa simplex (EBS)
INTERMEDIATE FILAMENTS
Other intermediate filaments
neurofilaments: high concentrations along the axons of vertebrate neurons
* Participate in axonal growth (length and diameter)
* Provide strength and stability to the axon
Lamin: mechanical stability of cell nucleus
Desmin: scaffold function for sarcomere (skeletal and cardiac muscle)
