Cytoskeleton & Response to Mechanical Stress Flashcards
Cytosol
Inside of cell → surrounds organelles
Cytoskeleton is a complex network of?
It extends through ____ and attaches to?
Complex network of interconnected filaments and tubules → extends throughout cytosol, attaches to inner surface of plasma membrane
Cytoskeleton plays a role in:
- Cell movement
- Cell division
- Internal organization (allows cell to assume shapes)
- Cell signaling
- Cell adhesion
Major structural elements of cytoskeleton
- Microtubules
- Microfilaments
- Intermediate fibers
Microtubule diameter
25 nm (largest)
Microfilaments diameter
7 nm (smallest)
Intermediate filament diameter
8-13 nm
Ways that microtubules, microfilaments and intermediate filaments/fibers are unique to each other
- Size
- Structure
- Intracellular distribution
- Formed by polymerization of different proteins
- Accessory proteins
Microtubule functions
- Cellular movement (cilia, flagella)
- Maintenance of nerves and axons
- Spatial orientation in cytosol → govern location of organelles
Microtubules are cylinders. Tell me about their characteristics.
- Hollow
- Straight
- Outer diameter = 25 nm, inner diameter = 15 nm
- Length varies
Wall of microtubule cylinders consists of:
13 protofilaments arranged side-by-side, forming a hollow center
Protofilament
Forms microtubule cylinder
Heterodimer of tubulin
2 types of tubulin
Alpha-tubulin
Beta-tubulin
beta-tubulin
2 functions:
Forms:
- Tubulin synthesis
- Non-covalent binding
Forms alpha-beta heterodimers
How many tubulin isoforms in brain?
5 alpha, 5 beta
Microtubule orientation
Radiate toward periphery → forms centrosome
How are microtubules regulated?
Microtubule associated proteins (MAPs)
Where do MAPs bind?
What is their function?
Regular intervals along wall of microtuble:
- Allows interaction with other filaments
- Regulate growth of microtubule
2 types of MAPs in brain
- Motor MAPs
2. Non-motor MAPs
Motor MAPs
Use ATP to drive transport of vesicles and organelles
Function of non-motor MAPs
- Control microtubule organism in cytoplasm
2. Nervous system
Neurites
Non-motor MAP in brain reinforced by microtubules
Neurites can differentiate into?
- Axons
2. Dendrites
Microfilament composes?
- Contractile fibers of muscle cells (actin)
- Microvilli
- Cell cortex
Cell cortex function
Mechanical support of plasma membrane → responsible for cell-surface movement
Cell cortex is a dense network of microfilaments. Tell me about it.
Microfilaments are attached to the inner face of plasma membrane → causes cell surface to be structurally rigid (important in cell shape)
Actin
- Extremely abundant → in virtually all cells
2. Building block of microfilaments
G-Actin
Individual actin
F-Actin (filamentous)
Polymerization of G-Actin
Actin nomenclature
- G-Actin
2. F-Actin
2 major groups of actin
- Muscle-specific
2. Non-muscle
Muscle-specific actin
apha-actin
Non-muscle actin
beta-actin and gamma-actin
Cell surface extensions
Extend from edge of migrating cell → aids in movement of cell
Actin-binding protein functions
- Stabilize filaments
2. Generate force (myosin)
Intermediate filament roles
- Structure
2. Tension-bearing
Intermediate filament properties
- Most stable
- Least soluble
- Scaffold (supports entire cytoskeleton)
Intermediate filament structure differs based on?
Amino acid composition between tissues
6 classes of intermediate filaments
I and II: epithelial cells III: muscle, glial, CT IV: nerve cels V: all cells VI: embryonic nervous system
How is mechanical stress important in normal physiological processes?
- Cell growth
- Function
- Differentiation
- Apoptosis
2 diseases in which mechanical stress is especially relevant
Heart and lung diseases
Adaptation from mechanical stress occurs via changes in:
- Structure
- Metabolism
- Gene expression
Tensegrity structure
Uses tension and compression to provide support
Tensegrity = tensional integrity
What generates tension?
Microfilaments
What bears compression?
Microtubules
What provides elasticity?
Intermediate filaments
How does cytoskeleton adapt to stress?
Transmits stress to rest of structure → aligns tension bearing forces with direction of stress
Signaling response to stress
ECM recognizes stress → transmits signal into cell so it can adapt as needed
3 responses to stress
- Outside-in signaling
- Regulation of nuclear access
- Adaptation of cytoskeleton and ECM
How is nuclear access regulated as a response to stress?
Alters pore size leading to nucelus
How does membrane respond to stress?
Mechanically gated ion channels
Centrosome
Microtubule organizing center
Neurites → Axons regulated by?
Tau
Neurites → Dendrites regulated by?
MAP2
Microfilaments found in what cells?
Almost all eukaryotic cells
Cell cortex is made of?
Dense network of microfilaments
Proper function of non-motor MAPs in the nervous system is dependent on?
Neuron and non-neuron interactions
