Cell Biology - Chapters 17 & 18: Cytoskeleton, Cell Motility, Cell Division, and Cell Death

Comprehensive vocabulary review flashcards covering Chapter 17 (Cytoskeleton & Cell Motility) and Chapter 18 (Cell Division, Cell Cycle & Cell Death).

Actin filaments

$7\,\text{nm}$ wide; made of G-actin; bind ATP; involved in cell shape and movement.

Microtubules

$25\,\text{nm}$ wide; made of alpha/beta-tubulin dimers; bind GTP; involved in transport and cell division.

Intermediate filaments

About $10\,\text{nm}$ wide; assembled from protein tetramers; provide mechanical strength; unpolarized.

Heterodimer

A complex made of two different protein subunits.

Tetramer

A complex made of four protein subunits.

Nucleation

Initial formation of a filament from protein subunits.

Dynamic instability

Rapid switching between microtubule growth and shrinkage.

Filament dynamics

Assembly, disassembly, and rearrangement of cytoskeletal filaments.

Tensile strength

Ability to resist pulling forces without breaking.

Elasticity

Ability to stretch and return to original shape.

Crosslinkers

Proteins that connect filaments into bundles or networks.

Dendritic array

Branching network of actin filaments.

Actin bundles

Groups of actin filaments held together by crosslinking proteins.

Filament widths

Actin: $7\,\text{nm}$; microtubules: $25\,\text{nm}$; intermediate filaments: about $10\,\text{nm}$.

Nucleotide binding

Actin: ATP; microtubules: GTP; intermediate filaments: none.

Filament polarity comparison

Actin and microtubules are polarized; intermediate filaments are unpolarized.

Motor proteins comparison

Actin: myosin; microtubules: kinesin and dynein; intermediate filaments: none.

Main functions comparison

Actin: shape/movement; microtubules: transport/organization; intermediate filaments: strength.

Role in cell division

Actin: cytokinesis; microtubules: chromosome separation; intermediate filaments: reorganize or disassemble.

Monomer

A single molecular subunit that can join with others to form a polymer.

Filament

Long, threadlike structure made of repeating protein subunits.

Polymerization

Process of joining smaller subunits together to form a polymer.

Filament polarity (ends)

Having two structurally different ends, called plus and minus ends.

Plus end

End of a polarized filament that generally grows faster.

Minus end

End of a polarized filament that generally grows more slowly.

Intermediate filaments (Function & Structure)

Unpolarized cytoskeletal fibers that provide mechanical strength and resist stretching.

Keratin

Intermediate filament protein that strengthens epithelial cells, hair, and nails.

Structure of mammal hair

Hair is primarily made of keratin proteins organized into strong filament bundles.

Lamins

Intermediate filament proteins that form the nuclear lamina and support the nucleus.

Microtubules (Structure & Transport)

Hollow cytoskeletal tubes made of tubulin that provide transport tracks and help separate chromosomes.

Alpha-tubulin

Protein that pairs with beta-tubulin to form a heterodimer; binds GTP.

Beta-tubulin

Protein that pairs with alpha-tubulin; hydrolyzes its bound GTP to GDP.

GTPase activity

Ability to hydrolyze GTP into GDP and inorganic phosphate.

Protofilament

Linear chain of tubulin dimers; typically $13$ form the wall of a microtubule.

Centriole

Cylindrical structure made of nine microtubule triplets.

Centrosome

Main microtubule-organizing center in animal cells; usually contains two centrioles.

MTOC

Microtubule-organizing center; site where microtubules are nucleated and organized.

Gamma-tubulin ring complex

Protein complex that nucleates microtubule formation and anchors their minus ends.

Basal body

Centriole-like structure that anchors and organizes cilia or flagella.

Cilia

Short, hairlike projections involved in cell movement, fluid movement, or sensing.

Flagella

Long, whiplike projections that propel cells through fluid.

Microtubule motors

ATP-powered proteins that transport materials along microtubules.

Vesicle transport

Movement of membrane-bound vesicles through the cell using motor proteins.

Kinesins

Motor proteins that generally move toward the plus end of microtubules.

Dyneins

Motor proteins that generally move toward the minus end of microtubules.

Spindle

Microtubule structure that separates chromosomes during cell division.

Asters

Star-shaped arrays of microtubules extending outward from spindle poles.

Actin

Cytoskeletal protein involved in cell shape, movement, and contraction.

G-actin

Globular actin monomer that binds ATP and polymerizes into F-actin.

F-actin

Filamentous polymer made of G-actin subunits; also called microfilaments.

Lamellipodium

Broad, sheetlike actin projection at the leading edge of a moving cell.

Filopodium

Thin, fingerlike actin projection involved in sensing and movement.

Microvillus

Small, actin-supported projection that increases cell surface area for absorption.

Brush border

Dense collection of microvilli on the surface of certain epithelial cells.

Stress fiber

Contractile bundle of actin and myosin that maintains tension and cell attachment.

Cortex

Thin cytoskeletal layer beneath the plasma membrane that supports cell shape.

Cortical actin

Network of actin filaments beneath the plasma membrane.

Phalloidin

Toxin that binds and stabilizes F-actin; fluorescent versions visualize actin filaments.

Monomer-binding proteins

Bind G-actin and regulate its availability for filament growth.

Profilin

Binds actin monomers and promotes their addition to growing filaments.

Nucleation factors

Proteins that help initiate the formation of new actin filaments.

Arp2/3 complex

Nucleates new actin filaments, creating branches from existing filaments.

Severing/depolymerizing proteins

Cut actin filaments or promote their disassembly.

Cofilin

Binds actin filaments and promotes severing and disassembly.

Crosslinkers/bundlers

Connect actin filaments into networks or bundles.

Fimbrin

Crosslinking protein that organizes actin filaments into tight bundles.

Capping protein

Binds filament ends to prevent further addition or removal of subunits.

Side-binding proteins

Bind along actin filaments and regulate their structure or function.

Tropomyosin

Binds along actin filaments and regulates interactions with other proteins, including myosin.

Myosin

ATP-powered motor protein that moves along actin filaments.

Actin-membrane linkers

Proteins that connect actin filaments to the cell membrane.

Dystrophin

Links actin to membrane-associated proteins, helping stabilize muscle cells.

Arp2/3 side-binding

Arp2/3 binds the side of an existing actin filament to initiate a new branch.

Dendritic (branched) array

Network of branching actin filaments, often formed by Arp2/3.

Rho family small G proteins

Molecular switches that regulate actin organization, cell shape, and movement.

Actin-binding proteins: overview

Profilin: monomers; Arp2/3: branching; cofilin: severing; fimbrin: bundling; capping protein: ends; tropomyosin: sides; myosin: movement; dystrophin: membrane linkage.

Migration

Movement of a cell from one location to another.

Polarization

Establishment of distinct front and back regions in a moving cell.

Leading edge

Front of a moving cell where actin polymerization pushes the membrane forward.

Trailing edge

Rear of a moving cell that retracts as the cell moves forward.

Protrusion

Extension of the cell membrane, usually driven by actin polymerization.

Attachment

Formation of connections between a cell and its surrounding surface.

Focal adhesion

Protein complex connecting actin filaments to extracellular matrix through integrins.

Contraction

Actin-myosin-generated force that helps move the cell body and retract the rear.

Steps of cell migration

Polarization, protrusion, attachment, then contraction and rear retraction.

Mitotic spindle

Microtubule structure that separates chromosomes during mitosis.

Karyokinesis

Division of the nucleus during cell division.

Contractile ring

Ring of actin and myosin that constricts to divide an animal cell.

Cytokinesis

Division of the cytoplasm to form two daughter cells.

Motor proteins

Proteins that convert chemical energy from ATP into mechanical movement.

Myosin superfamily

Family of motor proteins that move along actin filaments.

Myosin II

Motor protein that forms bipolar filaments and generates contractile force.

Head (motor domain)

Part of myosin that binds actin and ATP and generates movement.

Tail (coiled coil)

Region of myosin II that allows molecules to associate and form filaments.

Bipolar filament

Myosin filament with motor heads pointing outward in opposite directions.

Bare zone

Central region of a myosin thick filament that lacks projecting myosin heads.

Nonmuscle myosin II minifilament

Small bipolar myosin assembly that generates contraction in nonmuscle cells.

Muscle

Tissue specialized for contraction and force generation.

Skeletal muscle

Voluntary, striated muscle generally attached to bones.

Striated muscle

Muscle with repeating light and dark bands caused by organized sarcomeres.