Cell Biology Study Guide – Chapter 17 – Cytoskeleton (copy)

Cytoskeleton

A network of fibers that helps maintain cell shape, organizes cellular compartments, facilitates intracellular transport, and enables cell movement and division.

Intermediate Filaments (IFs)

Fibrous proteins providing mechanical support, especially in cells experiencing mechanical stress; they form networks from the nucleus to the cell periphery.

Actin Filaments

are thin and flexible

Microtubules

Hollow tubes that provide rigid support, long-range transport, and motility; composed of tubulin subunits.

Desmosome

A specialized junction connecting neighboring cells, often associated with intermediate filaments.

Hemi-desmosome

A junction that connects intermediate filaments to the extracellular matrix.

Keratins

A major class of intermediate filaments found in epithelial cells.

Vimentin

An intermediate filament protein associated with connective tissue, muscle, and glial cells.

Neurofilaments

Intermediate filaments providing mechanical support specifically in nerve cells.

Nuclear Lamins

Intermediate filaments forming a fibrous network lining the nuclear envelope.

Microtubule Organizing Center (MTOC)

A structure that organizes the assembly of microtubules, often associated with centrioles.

Mitotic Spindle

A structure formed during mitosis composed of microtubules that segregate chromosomes into daughter cells.

Dynamic Instability

The rapid assembly and disassembly of microtubules, essential for their function.

Kinesin

A motor protein that transports cellular cargo toward the plus end of microtubules.

Dynein

A motor protein that transports cellular cargo toward the minus end of microtubules.

Cilia

Short, hair-like organelles that beat to move fluids over cell surfaces. and beat in whiplike fashion

Flagella

Long, whip-like organelles that propel cells through fluid environments. and move like waves

Filopodia

Finger-like projections of actin filaments involved in cell movement.

Lamellipodia

Sheet-like projections of actin filaments involved in cell migration and movement.

Treadmilling

A dynamic process where actin filaments maintain a constant length while their subunits move from the plus to the minus end.

Cytochalasin

A toxin that binds to actin monomers and blocks polymerization.

Phalloidin

A toxin that binds to actin filaments and prevents depolymerization.

Myosin

A motor protein that interacts with actin filaments for muscle contraction and intracellular transport.

Sarcoplasmic Reticulum (SR)

An endoplasmic reticulum variant in muscle cells involved in calcium storage and release.

Calmodulin

A calcium-binding protein that regulates myosin activity in smooth muscle contraction.

Troponin

A protein complex that, in the presence of calcium, regulates the interaction of actin and myosin in muscle contraction.

T-Tubules

Invaginations of the plasma membrane in muscle cells that carry action potentials to the sarcoplasmic reticulum.

MyoD

A transcription factor that initiates myogenic differentiation and muscle gene expression.

Progeria

A rare genetic disorder caused by mutations affecting nuclear lamins, leading to premature aging.

Formins

• assemble actin filaments found in filopodia

• Bind to actin filament plus end

-45 different kinesin genes in human genome (14 classes)

-conserved motor domain that combines MT to ATP

Actin filaments plus and minus end

plus end: fast assembly, minus end: slow assembly

similar about actin and microtubule polymerization

• The rate of subunit addition is faster at the plus end than at the minus end.

• Nucleotide hydrolysis promotes the depolymerization of filaments.

• Free subunits (actin and tubulin) bind nucleoside triphosphates

Integrins

are transmembrane proteins that bind to the extracellular

matrix and connect it to the actin cytoskeleton at focal contacts

Myofibrils

• The cytoplasm of muscle cells is filled with organized

  arrays of contractile proteins

• Is a string sacromeres ( a basic unit of contraction)