Cell Anatomy - Cytoskeleton Flashcards
What is the cytoskeleton
System of protein filaments in the cytoplasm that gives a cell shape and the ability for directed movement
What are the three types of protein filaments
Microtubules
Actin filaments
Intermediate filaments
Rank the protein filaments from most –> least flexible
Intermediate
Actin
Microtubules
General properties - filament assembly
Self-assemble from small subunits- allows for rapid assembly/disassembly
Held together by weak, non-covalent bonds
How are filaments both stable and dynamic?
breaking a filament in the middle requires breaking many bonds, but requires little energy to remove subunits from the ends
What regulates the assembly of filaments?
Accessory proteins
Microfilaments dtructure
Globular actin monomers
Actin monomers bind ATP –>
Assemble to form a filament
2 parallel protofilaments twist to form a R helix
Do filaments have polarity?
yes
What end do filaments grow from?
The plus end
What part of the cell are microfilaments usually found?
Near the periphery
Microfilaments main functions:
Determine shape of the cell’s surface
Facilitate whole cell locomotion
What facilitates the ‘crawling’ of microfilaments
Actin polymerization
Microtubules: structure
-Globular tubulin subunits
-Tubulin monomers bind to GTp
-Alpha and beta monomers form dimers
-Protofilaments form hollow cylinder
Do microtubules have polarity
Yes. Subunits point in 1 direction, protofilamenst are parallel, grow from plus end
Where are microtubules usually located?
-Made in the microtubule organizing center (centrosome)
-Located near the nucleus
Main function of microtubules
-Determine the position of membrane-enclosed organelles
-Direct intracellular transport
Structure of intermediate filaments
-Rope-like
-assembled from subunits (keratins, neurofilaments, lamins)
-No associated nucleotide
-Alpha helical subunits dimerize into tetrameric subunits
-tetramerics pack together to form protofilament
-8 protofilaments form intermediate filament
Are intermediate filaments polar?
No
Location of intermediate filaments
Cells that are subject to mechanical stress
How are accessory proteins related to the cytoskeleton?
-Crosslink or bundle fibers
-Nucleate filament polymerization
-Cap/block polymerization
-Sever filaments
What are motor proteins
-Type of cytoskeleton binding protein
-Move molecules and enclosed organelles in the cell
-Generate the force required for contraction, ciliary movement, and cell division
How do motor proteins move
Use ATP hydrolysis to generate mechanical force that allows them to walk along microtubule and microfilaments
What are the major types of motor proteins
Myosin
Kinesin
Dynein
What are the filaments associated with each motor protein
Myosin - microfilaments (actin)
Kinesin - microtubules
Dynein - microtubules
Structure of molecular motors
-head region - binds and hydrolyzes ATP
-Tail region - binding site for ‘cargo’
Kinesin - structure
2 globular head domains
Dynein - structure
2 or 3 main proteins plus a variable number of associated polypeptides
What is the largest and fastest molecular protein
Dynein
Kinesis ‘walks’ towards which end of the filaments
The plus end
Kinesis - how it moves
Hydrolysis of ATP changes conformation of protein, allowing it to walk along the microtubules
Dynein - how it moves
Nucleotide hydrolysis + MT binding and unbinding + force generating conformational change
Power stroke also driven by ATP hydrolysis, causes head to rotate and generate a step
Dynein walks towards which end of the microtubule?
The minus end
Kinesin - funtion
Bring cargo to periphery of cell
Organelle positioning
Axonal transport
Mitosis
Dynein - funtion
Bring cargo to center of the cell
Cilia beating
Vesicle transport
Mitosis
Subunits of microfilaments
Actin
Subunits of microtubules
Tubulin
Subunits of intermediate filaments
keratin
Microfilaments bind…
ATP
Microtubules bind…
GTP
