Cytoskeletal Systems and Their Functions

Cytoskeleton

Network of filaments and tubules in cytosol.

Microtubules

Largest cytoskeletal elements, 25 nm in diameter.

Microfilaments

7 nm wide, composed of actin subunits.

Intermediate Filaments

8-12 nm, variable composition in cells.

Septins

Protein network located within cells.

MreB

Actin-like protein in bacteria for DNA segregation.

FtsZ

Tubulin-like protein regulating bacterial division.

Crescentin

Protein regulating bacterial cell shape.

Axonemal Microtubules

Stable microtubules in cilia and flagella.

Cytoplasmic Microtubules

Microtubules maintaining axons and cell shape.

Protofilaments

Longitudinal arrays forming microtubules.

Tubulin Heterodimers

Building blocks of microtubules, α and β subunits.

Microtubule Polarity

Distinct chemical properties at plus and minus ends.

Tubulin Isoforms

Variants of α- and β-tubulin proteins.

Singlet Microtubules

Simple tubes with 13 protofilaments.

Doublet Microtubules

Contain A tubule and one additional incomplete ring.

Triplet Microtubules

Contain A tubule and two additional incomplete rings.

Nucleation

Initial aggregation of tubulin dimers for microtubule formation.

Elongation

Addition of tubulin subunits at microtubule ends.

Lag Phase

Slow initial phase of microtubule assembly.

Plateau Phase

Balance of microtubule assembly and disassembly.

Critical Concentration

Tubulin concentration balancing assembly and disassembly.

Cilia

Hair-like structures for cell movement.

Flagella

Long structures for cell propulsion.

Microtubule-Associated Proteins (MAPs)

Proteins that interact with microtubules.

Colchicine

Chemical that binds to microtubule subunits.

Dynamic Cytoskeleton

Cytoskeleton constantly assembled and disassembled.

Cell Wall Growth

Orientation of cellulose microfibrils in plants.

Vesicle Movement

Transport of vesicles within the cell.

Microtubule Plus End

Rapidly growing end of microtubules.

Microtubule Minus End

Slowly shrinking end of microtubules.

Treadmilling

Addition at plus end, removal at minus end.

Vinblastine

Antimitotic drug from periwinkle plant.

Nocodazole

Inhibits microtubule assembly, reversible effects.

Paclitaxel (Taxol)

Stabilizes microtubules, used in cancer treatment.

Dynamic Instability

Alternating growth and shrinkage of microtubules.

GTP Cap

Prevents subunit removal at microtubule ends.

Catastrophe

Switch from growth to shrinkage in microtubules.

Rescue

Switch from shrinkage back to growth phase.

Microtubule-Organizing Center (MTOC)

Site of microtubule assembly in cells.

Centrosome

MTOC associated with centrioles in animal cells.

Centriole

Structure formed by triplet microtubules.

γ-Tubulin

Protein crucial for microtubule nucleation.

γ-Tubulin Ring Complexes (γ-TuRCs)

Nucleate microtubule assembly away from centrosome.

Ninein

Microtubule minus-end binding protein.

Augmin

Anchors branched microtubule structures.

Microtubule Treadmilling

Dynamic equilibrium of tubulin addition and removal.

GTP Hydrolysis

Contributes to microtubule dynamic instability.

Basal Bodies

Structures at the base of cilia.

Actin Monomers

Building blocks for microfilaments.

Cytochalasin D

Prevents addition of actin monomers.

Phalloidin

Stabilizes assembled microfilaments.

Acrylamide

Causes loss of intermediate filament networks.

Vincristine

Related to vinblastine, used in cancer therapy.

Microtubule Assembly

Process of tubulin polymerization into microtubules.

MTOC

Microtubule-organizing center; anchors microtubules.

Microtubule (MT)

Cylindrical structures aiding cell shape and transport.

MAPs

Microtubule-associated proteins regulating stability and structure.

Tau

MAP that bundles microtubules in axons.

MAP2

Promotes looser microtubule bundles in dendrites.

+-TIP Proteins

Stabilize growing plus ends of microtubules.

End-binding protein 1 (EB1)

A +-TIP protein stabilizing MT plus ends.

Stathmin/Op18

Destabilizes microtubules by binding tubulin heterodimers.

Catastrophins

Promote peeling of subunits from MT ends.

Katanin

Severs microtubules for destabilization.

Actin

Protein building block of microfilaments.

G-actin

Globular actin monomer that binds ATP or ADP.

F-actin

Polymerized form of G-actin, forms microfilaments.

Polarity of Microfilaments

Rapid addition of G-actin at plus end.

Cytochalasins

Prevent addition of new monomers to microfilaments.

Latrunculin A

Sequesters actin monomers, preventing polymerization.

Microvilli

Structural core formed by microfilaments.

Amoeboid Movement

Cell movement driven by microfilament dynamics.

Cell Cortex

Region beneath plasma membrane supported by microfilaments.

Myosin

Motor protein interacting with actin for contraction.

Arrowhead Pattern

S1 fragments bind to actin, indicating polarity.

Elongation Phase

Rapid growth phase of microfilament assembly.

Stress fibers

Organized bundles of actin in adherent cells.

Cell cortex

Actin gel beneath the plasma membrane.

Lamellipodia

Branched actin network aiding cell movement.

Filopodia

Polarized actin cables at cell's leading edge.

Actin-binding proteins

Proteins regulating actin assembly and organization.

Profilin

Competes with thymosin for G-actin binding.

Thymosin β4

Sequesters G-actin, limiting free concentration.

ADF/cofilin

Increases turnover of ADP-actin at minus end.

Arp2/3 complex

Nucleates actin branches on filament sides.

Capping proteins

Prevent addition or loss of actin subunits.

CapZ

Caps plus ends of actin filaments.

Tropomodulin

Caps minus ends of actin filaments.

Filamin

Crosslinks actin filaments into networks.

Gelsolin

Severs actin filaments and caps plus ends.

α-Actinin

Bundles actin in focal contacts and adhesions.

Fascin

Maintains tight bundling of actin in filopodia.

Fimbrin

Crosslinks actin in microvilli bundles.

Villin

Stabilizes actin bundles in microvilli.

Terminal web

Network of filaments at microvillus base.

Spectrin

Links actin to cell membranes.

Ankyrin

Connects spectrin to membrane proteins.

WASP

Activates Arp2/3 for actin branching.

Formins

Promote actin polymerization independently of Arp2/3.