Cytoskeleton Flashcards
What are the three types of filaments that make up the cytoskeleton?
- Actin filaments (microfilaments)
* Polymers of actin monomers
* Linked to each other by actin-binding proteins - Microtubules
* Tubulin polymers
* Linked to each other by microtubule-associated proteins
* 25 nm (thickest cytoskeletal elements)
* Form mitotic spindles (segregate chromosomes during cell division) - Intermediate filaments
* Provide mechanical support
* Keratin filaments - keratin
* Neurons - peripherin
What helps link cytoskeletal filaments to each other and the plasma membrane?
Accessory proteins
Microtubules
- minus end - alpha-tubulin facing end
- plus end - beta-tubulin facing end; where new tubulin dimers bind
- Kinesin - plus-end headed
- Dynein - minus-end headed
Which cytoskeletal filaments are made up of asymmetric protein monomers?
- Actin filaments (microfilaments) - globular actin
- Microtubules - alpha-beta tubulin heterodimers
How are cytoskeletal filaments subunits/monomers held together?
Weak associations (non-covalent interactions and hydrophobic forces)
(1) What are the two ways actin filaments can be assembled? (2) What helps actin filaments assemble this way?
(1)
1. Parallel arrays
2. Complex 3-dimensional networks
(2) Actin-binding proteins
How are microtubules assembled?
- aB tubulin heterodimer assemble end-to-end to form hollow cylinder made up of 13 protofilaments
What are the functions of microtubule-associated proteins (MAPs)?
- Help filaments polymerize
- Stabilize assembled structure
How are intermediate filaments assembled?
- Elongated fibrous proteins form tetramers
- Tetramers associate to form rigid rope-like structure
Where do microtubules originate from?
Microtubule organizing centers (MTOCs)
How do microtubules contribute during cell division?
Microtubules help from spindle apparatus (segregates chromosomes to daughter cells)
What is dynamic instability? Which type of cytoskeletal components exhibits this? What happens during this process?
(1) Unpredictable change between growth and shrinkage
(2) Microtubules
(3)
* Catastrophe - shift from growth to shrinkage
- Rescue - shift from shrinkage to growth
- Tubulin heterodimer
- beta subunit bound to hydrolyzable form of GTP
- Hydrolysis of GTP to GDP destabilizes microtubule framework –> depolymerization of microtubule
How do regulatory proteins control microtubule dynamics?
MAPs - promote microtubule stability
Catastrophe factors - destabilize microtubules
?
Interphase - microtubules radiate from centrosome
Mitosis - duplicated centrosomes move towards opposite poles microtubule instability increases
What are the two superfamilies of microtubule associated motor proteins? Describe each of them.
- Kinesin
- Globular heads - binds to microtubules
- Stalk - connects to fan-shaped receptors
- Fan-shaped receptor - binds to organelles and vesicles
- Move cargos toward cell periphery using hand-over-hand movement - Dynein
- Heavy chain - globular head (responsible for energy generation) and stalk (responsible for binding with microtubules
- Light chain
- Intermediate chain
- Light-intermediate chain
- Move organelles and vesicles towards other organelles toward center of cell
ATP
What is cell migration?
Process by which cells move from one location to another
What process is cell migration important?
Development
Give an example of cell migration.
- Physical trauma to cells induces release of growth factors
- Fibroblasts respond to signals by protruding their membrane in direction of signal (leading edge)
- Trailing edge - localized anti-adhesive signals initiate retraction of focal adhesions
