cytoskeletal systems

Microtubules

Thickest cytoskeletal filaments, rigid hollow tubes.

Intermediate Filaments

Middle layer, diverse structures, various functions.

Microfilaments

Thinnest cytoskeletal filaments, involved in movement.

Cytoskeleton

Dynamic network providing structure and transport.

Tubulin Heterodimers

Protein building blocks of microtubules, α and β.

Protofilaments

Longitudinal arrays of polymers in microtubules.

Cytoplasmic Microtubules

Microtubules in cytosol for various functions.

Axonemal Microtubules

Stable microtubules in cilia and flagella.

Singlet Microtubules

Simple tubes with 13 protofilaments.

Doublet Microtubules

Cilia and flagella structures with two tubule types.

Triplet Microtubules

Basal bodies and centrioles with three tubules.

Kinetics of MT Assembly

Phases: lag, elongation, plateau in microtubule growth.

Critical Concentration

Tubulin concentration for balanced assembly/disassembly.

Plus End

Rapidly growing end of microtubules.

Minus End

Anchored end of microtubules at MTOC.

Microtubule-Organizing Center (MTOC)

Site where microtubules originate, often centrosome.

Centrosome

MTOC with two centrioles near the nucleus.

Centrioles

Structures composed of triplet microtubules, aid in division.

γ-Tubulin

Nucleates microtubule assembly in centrosomes.

Antimitotic Drugs

Interfere with microtubule dynamics, inhibit cell division.

Colchicine

Binds β-tubulin, inhibits microtubule assembly.

Taxol

Stabilizes microtubules, prevents disassembly.

Microtubule-Binding Proteins

Regulate microtubule stability and dynamics.

MAPs

Microtubule-associated proteins that stabilize microtubules.

Tau

MAP that bundles microtubules in axons.

MAP2

Promotes looser microtubule bundles in dendrites.

+TIP Proteins

Stabilize growing plus ends of microtubules.

Catastrophins

Destabilizing proteins that promote microtubule disassembly.

Microfilaments Function

Involved in muscle contraction and cell movement.

Actin

Globular protein forming microfilaments, binds ATP.

G-actin

Monomeric form of actin, polymerizes to F-actin.

Microfilaments

Cytoskeletal components aiding cell shape and motility.

Cell Cortex

Region beneath plasma membrane with microfilaments.

Actin

Abundant protein forming microfilaments in eukaryotes.

G-actin

Globular actin monomer that binds ATP or ADP.

F-actin

Filamentous actin formed by polymerized G-actin.

Polarity of Microfilaments

Uneven growth rates at plus and minus ends.

Lag Phase

Initial delay in G-actin polymerization to filaments.

Elongation Phase

Rapid addition of G-actin to growing microfilaments.

Microfilament Structure

Two strands of polymerized G-actin in a helix.

Stress Fibers

Organized bundles of actin in adherent cells.

Lamellipodia

Broad, sheet-like extensions of crawling cells.

Filopodia

Thin, finger-like projections with polarized actin.

Microvilli

Cellular extensions increasing surface area, found in intestines.

Crosslinking Proteins

Proteins like fimbrin and villin stabilize microfilaments.

Formins

Proteins that promote actin filament growth at plus ends.

Profilin

Binds ATP-G-actin, facilitating microfilament assembly.

Rho Family GTPases

Regulatory proteins influencing actin structure formation.

Rho GTPase

Promotes stress fiber formation in cells.

Rac GTPase

Stimulates lamellipodia extension in motile cells.

Cdc42 GTPase

Induces filopodia formation at cell edges.

Guanine-nucleotide Exchange Factors (GEFs)

Activate Rho GTPases by exchanging GDP for GTP.

GTPase Activating Proteins (GAPs)

Inactivate Rho GTPases by hydrolyzing GTP.

Guanine-nucleotide Dissociation Inhibitors (GDIs)

Sequester inactive Rho GTPases in the cytosol.

Intermediate Filaments

Stable cytoskeletal components, not found in plant cells.

Keratin

Common intermediate filament protein in animal skin.

Protofilaments

Basic structural units of intermediate filaments.

Spectraplakins

Linker proteins connecting different cytoskeletal components.

Cytoskeleton

Integrated structure providing mechanical support and motility.

Motor Proteins

Proteins generating movement along cytoskeletal filaments.