Cytoskeleton Flashcards
3 types of protein filaments
Intermediate filaments
Microtubules
Actin filaments (also known as microfilaments)
Intermediate filaments
Span cytosol and link adjacent cells at desmosomes
Give strength to animal cells- allow stretching
Form cell-cell junctions
10 micrometers diameter
Rope-like strands
Often associated with other proteins
Keratins
Intermediate filaments in epithelia
Vimentin
Intermediate filaments in connective tissue, muscle cells, and glial cells
Neurofilaments
Intermediate filaments in nerve cells
Nuclear lamins
Nuclear intermediate filaments in all animal cells
Nuclear division
Phosphorylation of lamin (nuclear filament) causes lamina to dissemble
Reassembly following telophase
Dephosphorylation of lamina
Microtubule locations
Interphase cell: attached to centrosome
Dividing cell: mitotic spindles
Ciliated cell: attached to basal body
Tubulin
Subunit of microtubules
Attach end to end, giving an alpha (minus) end and a beta (plus) end (polarity)
Centrosome and microtubules
Microtubules grow from gamma-tubulin ring complex
Polymerization of microtubules
Independent in each microtubule
Depends on tubulin-GTP availability
Dynamic instability: alternates between growing and shrinking
GTP-tubulin stabilizes the end of the microtubule, causing growth of microtubule
GTP hydrolysis: protofilaments containing GDP tubulin peel away from the microtubule wall and GDP tubulin is released into the cytosol
Microtubule-specific drugs
Anti-cancer drugs (taxol, colchicine, vinblastine, etc.)
Bind and stabilize microtubules and subunits, preventing polymerization
Cell can’t divide, nervous system doesn’t work properly (microtubules allow transport along neurons)
Capping proteins
Stabilize microtubules, resulting in polarization of cell
Kinetochore microtubules
Connect to kinetochore (hold sister chromatids together)
Movement of cell parts based on motor proteins
Microtubules and nerve cells
Establish polarity of nerve cells
Provide tracks for movement of cargo
Dynein
Motor protein that uses microtubules as tracks for movement
Moves towards minus (alpha) end of microtubule
Kinesin
Motor protein that uses microtubules as tracks for movement
Moves towards plus (beta) end of microtubule
“Walking” of motor proteins by ATP hydrolysis
ATP binds
Hydrolysis
Release of ADP
Conformational change of motor protein, moving it forward
Motor protein function
Transport of cargo
Vesicles with proteins destined for secretion or endocytosis, etc.
Microtubules and ER and Golgi
Organization of ER and Golgi
Cilium and flagellum cross section
9+2 array of microtubules: prevents sliding of microtubules
Dynein acts on filaments held together by nexin
Roles of actin filaments
Maintenance of shape and contraction
Microvilli, contractile fibers, amoeboid movement, cell cleavage
Microvilli
Actin filaments that increase surface area (don’t move)
Increased absorption
Structure of actin filaments
Assemble with directionality
Plus end and minus end
Actin filament polymerization
Can proceed from either end
ATP bound actin binds to other actin particles
Actin with bound ADP dissembles
Protein interaction with actin
Critical for actin function Nucleating protein (control where actin binds), bundling protein (in filopodia), motor protein (myosin), capping protein, cross-linking protein (in cell cortex)
Actin in the cell cortex
Gives cell cortex structure
Amoeboid movement
Actin polymerization at plus end protrudes lamellipodium (finger-like projections)
Myosin causes contraction at other end
ARP complex
Branch point of actin filaments
Actin-myosin mediated contraction
Moves membrane vesicles and allows contraction of membrane
GTP binding proteins
Actin filaments respond to signaling by these
Myosin-II molecule
Muscle myosin
Contractile ring
Myosin-actin interaction
Cell division: pinching off of cells
Contractile bundles
Myosin-actin interaction
Amoeboid movement
Sarcomere
Contractile unit of muscle
Compose myofibrils which compose muscle cells
Z disc
Anchorage of actin filaments in muscle
Muscle contraction by ATP hydrolysis
Attachment: myosin head lacking a bound nucleotide is locked tightly onto an actin filament in a rigor configuration
Release: molecule of ATP binds to back of myosin head and causes myosin to lose affinity for actin and move among the filament
Cock: Head closes around the ATP molecule and hydrolysis of ATP occurs
Force-generation: Myosin binds weakly to actin, causing release of phosphate produced by ATP hydrolysis
Release triggers power stroke, moving myosin forward
ADP is released, and myosin reattaches to actin
Sarcoplasmic reticulum
Calcium storage in the muscle cell
Transverse (T) tubules
Formed from invaginations of plasma membrane
Used for signaling in muscle cell
Release of calcium in muscle cells
Depolarization of T-tubule membrane opens voltage gated calcium channel
Ca+2 is released into cytosol and binds to calcium release channel of sarcoplasmic reticulum membrane, releasing calcium from sarcoplasmic reticulum
Tropomyosin
Responds to calcium
Attached to actin
Normally blocks myosin-binding site, but when exposed to calcium, it moves, allowing myosin to move
