Cytoskeleton Flashcards
Cytoskeleton
Network of protein filaments placed in the cytoplasm
Function of cytoskeleton
Allows cell to change its shape, move organelles & move from place to place
Intermediate filaments
Rope-like fibrous proteins
Least dynamic
10nm in diameter
Function of intermediate filaments
Provide cell shape & structural reinforcement
Anchor organelles
Keep nucleus in place
Actin filaments
Made of globular protein actin
7nm in diameter
ATP dependent, filament is polar, dynamic instability
Molecular motors of actin filaments
Myosin I & II
Function of actin filaments
Structural
Movement (amoeboid, muscle)
Mitosis (contractile ring)
Microtubules
Tubes of globular protein tubulin
25nm in diameter
GTP dependent, polar, dynamic instability
Microtubule organising centers
Centrosome
Mitotic spindle
Basal body
Function of microtubules
Maintain cell shape
Anchor organelles
Movement (ciliar, flagellar, intracellular)
Mitosis ( mitotic spindle)
The principle of mvement
Transformation of chemical energy into mechanical
Molecular motor is composed of
Motor (head) domain
Tail (stalk) domain
Motors associated with microtubules
Dynein
Kinesin
Types of motor movement
Cytoskeletal structure is fixed
Sliding
Motor is fixed
Cytoskeletal structure is fixed
Head binds to cytoskeletal structure that is fixed
Hydrolysis of ATP
Head change conformation & move along cytoskeletal structure
Cargo moves with motor
Sliding
Motor is fixed with stalk to one cytoskeletal structure while head contacts other cytoskeletal structure
Cause sliding
Intracellular transport
Transport of secretory vesicle by molecular motors (D,K) along MT highway
Centriole
Made of MT
Duplicate during S phase
Migrate to opposite poles of cell
Form organizing centers for mitotic spindles
Flagella & Cilia structure
Basal body
Axoneme (MT & radial spokes)
Dynein
Principle of flagellar & ciliar movement
Stalk of D is fixed to A subunit of MT doublet
Head of D contact B subunit of neighboring MT doublet causing hydrolysis of ATP
Activated head changes its conformation
Why do MT doublets in ciliary & flagelllar movement flex?
Because the MT doublets are fixed by radial spokes
Function of flagellar & cilliary movement
Move things along surface of cell that lines lumen
Used in locomotion (sperm cell)
Bacterial flagellum Composition
Filament composed of flagellin
Hook outside outer membrane
Basal body rings
Types of bacteria based on flagellum
Monotrichous
Lophotrichous
Amphitrichous
Peritrichous
Amoeboid movement principle
Movement is based on changing shape of cell by forming false feet (pseudopods)
Amoeboid movement
Protrusion of pseudopodium
Pseudopodium is attached
Rest of the cell body is pulled
Muscle contraction
1) AP transmits signal down axon
2) AP activates V-gated Ca, Ca rush in
3) Ca cause vesicles to release acetylcholine into synaptic cleft
4) opening of Na/K channel
5) AP spreads through muscle fiber’s network of T tubules
6) Depolarization activates V-gated Ca channel that interact with Ca-release channels of SR to activate them & release Ca
7) Ca binds to troponin C that modulates tropomyosin that moves
8) Myosin binds, pulls Z-disk towards each other & shortens sarcomere
Muscle relaxation
After no signal, Ca is pumped to Sr by Ca pump
Tropomyosin changes conformation back to its previous state to block binding sites of actin
Prophase
Mitotic spindle is formed
Centrosome
Organizing centrum for MT
Duplicated in S phase
Prometaphase
K MT attach to each sister chromatid at the kinetochore
Metaphase
Chromosomes line up on the equator of the cell by polymeration & depolymeration of K MT
Anaphase
Dynein pulls chromatids to opposite poles
P MT slide (with help of Kinesin)
Telophase
K MT disappear
P MT still polymerate
Cytokinesis (Animal Cell)
Process = cleavage
Contractile ring is formed
Actin filaments slide (by help of myosin II)
Cytokinesis (Plant Cell)
Vesicles from GA move along MT to equator of cell & fuse
Produce cell plate
Bacterial flagellum composition
Filament flagellin
Hook
Basal body rings
Bacterial flagellum principles
Flow of protons
Rotates independently
Thick 6 hollow (addition of flagellin subunits at tip)
Archaeal flagellum principle
Powered by ATP
Rotate as a single flagellum
Addition of subunits to base
