Cell Bio Test #3

ALS

Amyotrophic lateral sclerosis, a progressive neurodegenerative disease caused by mutations in neurofilament genes that disrupt axonal transport and lead to motor neuron death.

Coiled-coil

A protein structural motif where two alpha-helices wind around each other, forming the basic dimerization unit of intermediate filament proteins

EBS-MD

Epidermolysis bullosa simplex with muscular dystrophy, a severe form of EBS caused by mutations in plectin that affects both skin integrity and muscle function

Epidermolysis bullosa simplex

A blistering skin disease caused by keratin mutations that weaken intermediate filaments in the epidermis, making skin fragile and prone to tearing under mechanical stress

Keratin

A family of intermediate filament proteins found in epithelial cells that provide mechanical strength to tissues like skin, hair, and nails

KASH

Klarsicht/ANC-1/Syne homology domain, a C-terminal domain on nesprin proteins that spans the outer nuclear membrane and binds to SUN proteins in the perinuclear space

LINC complex

Linker of Nucleoskeleton and Cytoskeleton, a protein bridge composed of SUN and KASH proteins that physically connects the nuclear lamina to the cytoskeleton to transmit mechanical forces

Neurofilament

Intermediate filament proteins found exclusively in neurons that regulate axonal diameter and are essential for proper nerve signal conduction

Nuclear lamin

Type V intermediate filament proteins that form the nuclear lamina, a meshwork underlying the inner nuclear membrane that provides structural support and organizes chromatin

Plectin

A large cross-linking protein that tethers intermediate filaments to other cytoskeletal elements and to cell junctions like desmosomes and hemidesmosomes

SUN

Sad1/UNC-84 domain, an N-terminal domain on proteins embedded in the inner nuclear membrane that binds to lamins and interacts with KASH domains in the perinuclear space

Vimentin

A type III intermediate filament protein found in mesenchymal cells like fibroblasts and muscle cells that provides flexible scaffolding and maintains cell shape

alpha tubulin

One of the two globular protein subunits that make up a tubulin dimer; it pairs with β-tubulin to form the basic building block of microtubules

beta tubulin

The second globular protein subunit in a tubulin dimer; it binds GTP and its hydrolysis to GDP drives microtubule dynamic instability

Tubulin dimer

heterodimer composed of one α-tubulin and one β-tubulin subunit; these dimers polymerize head-to-tail to form protofilaments and ultimately microtubules

Gamma tubulin

specialized tubulin isoform that forms ring complexes (γ-TuRCs) at microtubule organizing centers; it nucleates microtubule assembly by providing a template for αβ-tubulin dimers to attach

Protofilament

linear chain of tubulin dimers arranged head-to-tail; 13 protofilaments align side-by-side in a circular arrangement to form the hollow wall of a microtubule

Centrosome

primary microtubule organizing center (MTOC) in animal cells, containing a pair of centrioles surrounded by pericentriolar material; it anchors the minus ends of microtubules and nucleates their growth

Centrioles

Barrel-shaped structures composed of nine triplet microtubules arranged in a cylinder; they organize the centrosome and play key roles in cell division and cilium/flagellum formation

Dynamic instability

The property of microtubules to switch stochastically between phases of slow growth and rapid shrinkage; this behavior allows cells to rapidly remodel their microtubule network and is driven by GTP hydrolysis and cap stability

GTP

nucleotide that binds to β-tubulin in a dimer; GTP-bound tubulin promotes microtubule growth, while hydrolysis to GDP promotes shrinkage

Kinesin

A family of motor proteins that walk toward the microtubule plus end; they transport cargo like vesicles and organelles along microtubule tracks, typically moving from the cell center outward

Dynein

A motor protein that moves toward the microtubule minus end; it transports cargo toward the cell center and generates the bending force in cilia and flagella through microtubule sliding

Antimitotic drug

A class of therapeutic agents that disrupt microtubule dynamics to arrest cell division; they either promote depolymerization or excessive stabilization, preventing proper spindle formation

Colchicine

An antimitotic drug that binds free tubulin dimers and prevents their polymerization; it blocks microtubule assembly, causing spindle failure and cell cycle arrest

Taxol

An antimitotic chemotherapy drug that stabilizes microtubules by binding to their interior surface; it prevents depolymerization, "freezing" the microtubule network and blocking cell division

Actin

A globular protein that serves as the monomeric building block of microfilaments and is essential for maintaining cell shape and generating movement

Actin filament

A flexible, polar polymer ~7 nm in diameter composed of actin subunits, possessing fast-growing plus ends and slower minus ends that enable treadmilling and force generation

ARP complex

The Actin-Related Protein 2/3 complex nucleates new actin filaments and assembles them into branched networks that drive membrane protrusion

Filopodia

Slender, finger-like projections at the cell’s leading edge formed by parallel bundles of actin filaments, often stimulated by Cdc42 to probe the extracellular environment

Formins

Actin-nucleating proteins that promote the assembly of long, unbranched actin filaments and straight bundles rather than branched networks

Lamellipodia

Broad, veil-like membrane protrusions at the leading edge of crawling cells generated by a dense, branched actin meshwork

Phalloidin

A bicyclic peptide toxin that binds actin filaments and prevents depolymerization, effectively freezing filament dynamics

Profilin

An actin-binding protein that promotes the exchange of ADP for ATP on actin monomers and helps deliver them to growing filament plus ends

Thymosin beta4

A small actin-sequestering protein that binds ATP-actin monomers, helping maintain a large cytoplasmic pool available for polymerization

Myosin II

A bipolar motor protein with ATPase heads that forms thick filaments and powers muscle contraction by "walking" along actin filaments

Sarcoplasmic reticulum

specialized endoplasmic reticulum in muscle cells that stores and releases calcium ions to trigger contraction

Sarcomere

The fundamental contractile unit of a muscle fiber, composed of repeating interdigitated actin and myosin filaments that slide past each other during contraction

T-tubule

An invagination of the muscle cell membrane that rapidly transmits action potentials deep into the fiber to stimulate calcium release from the sarcoplasmic reticulum

Troponin

A calcium-binding protein complex on thin filaments that, when bound by Ca²⁺, initiates a conformational change to move tropomyosin and expose myosin-binding sites on actin

Tropomyosin

A regulatory protein that blocks myosin-binding sites on actin in relaxed muscle; it shifts away upon calcium-triggered troponin binding to allow contraction

Z disc

A protein structure that anchors the thin (actin) filaments and defines the boundaries of each sarcomere