Cytoskeleton and Microtubule Functions in Cells Module 8 Final

Microtubules

Assembled from the protein tubulin

Actin filaments

One of the three filamentous structures that compose the cytoskeleton

Intermediate filaments

One of the three filamentous structures that compose the cytoskeleton

Cytoskeleton

Provides structural support to the cell

Functions of the cytoskeleton

Structural support, organelle positioning, material movement

Microtubule structure

Protofilament ↔️ Longitudinal rows of tubulin

αβ-tubulin heterodimer

One α-tubulin and one β-tubulin subunit

Plus end of microtubules

Row of β-tubulin subunits

Minus end of microtubules

Row of α-tubulin subunits

Microtubule-associated proteins (MAPs)

Proteins that stabilize microtubules

Tau

A MAP implicated in Alzheimer's disease due to abnormally high phosphorylation

Cell shape in animal cells

Radial array from the nucleus

Microtubule transport defects

Examples include ALS and Lou Gehrig's disease

Motor proteins

Use ATP hydrolysis to generate movement along microtubules

Motor protein superfamilies

Kinesin, dynein, myosin

Kinesin

The smallest and best understood microtubular motors

Kinesin structure

Tetramer of two heavy and two light chains

Kinesin movement direction

Moves toward the plus end of microtubules

Hand-over-hand mechanism

Processive movement along microtubules used by kinesins

Kinesin-mediated transport

Tends to move cargo outward toward the cell's membrane

Cytoplasmic dynein role

Moves cargo toward the minus end

Cytoplasmic dynein function in mitosis

Positions the spindle during mitosis

Microtubule-organizing centers (MTOCs)

Specialized structures for microtubule nucleation

Centrosome

The major MTOC in animals

Microtubule growth

Grow at their plus ends and remain anchored at the MTOC

Basal body

MTOC at the base of cilia or flagella

γ-tubulin

A critical protein in microtubule nucleation

Cytoskeleton

Network providing structural support and shape to cells.

Microtubule Organizing Centers (MTOCs)

Structures that organize microtubule assembly in cells.

Dynamic instability

Microtubules can rapidly grow and shrink.

GTP-tubulin

Active form of tubulin promoting microtubule growth.

GDP-tubulin

Inactive form of tubulin leading to microtubule shrinkage.

Cilia

Hairlike organelles for movement and sensing in cells.

Flagella

Long, whip-like structures for cell motility.

Intermediate filaments

Cytoskeletal components providing mechanical strength.

Mitotic spindle

Microtubule structure separating chromosomes during cell division.

Microtubule stability

Determined by microtubule-interacting proteins like MAPs.

Posttranslational modifications

Chemical changes to proteins after synthesis affecting function.

Hydrostatic pressure

Pressure exerted by a fluid, affecting microtubule stability.

Cold temperature

Environmental factor inducing microtubule disassembly.

Calcium concentration (Ca2+)

Elevated levels can trigger microtubule disassembly.

Cilium

Short, hair-like structure for movement or sensing.

Flagellum

Long, whip-like structure for cell motility.

Basal body

Structure from which cilia and flagella emerge.

Axoneme

Core structure of cilia and flagella.

9 + 2 array

Nine doublet microtubules surrounding two central microtubules.

Intermediate filaments

Strong, flexible fibers providing mechanical strength.

Keratin

Intermediate filament protein in epithelial cells.

Vimentin

Intermediate filament found in mesenchymal cells.

Desmin

Intermediate filament protein in muscle cells.

GFAP

Intermediate filament protein in astrocytes.

Neurofilament proteins

Intermediate filaments in neurons.

Plectin

Protein connecting intermediate filaments to other filaments.

Tetramer

Basic subunit formed by two dimers in IF assembly.

Dimers

Two monomers associated in parallel orientation.

Assembly of IFs

Does not require ATP or GTP involvement.

Phosphorylation

Regulates assembly and disassembly of intermediate filaments.

Desmosomes

Cell structures anchoring keratin IFs at cell edges.

Hemidesmosomes

Anchors keratin IFs to the extracellular matrix.

Neurofilaments function

Support and maintain structure in neuronal axons.

Unit length of IF

Formed by eight tetramers in intermediate filaments.

Chemical heterogeneity

Diverse protein composition of intermediate filaments.

Intermediate filament architecture

Monomers form dimers, then tetramers, then filaments.

Mechanical stress absorption

Function of keratin IFs in epithelial cells.

Cytoskeletal elements

Components that provide structure and support to cells.

Cytoskeleton

Skeletal system of eukaryotic cells.

Microtubules

Hollow, rigid structures made of tubulin.

Actin filaments

Thin filaments aiding in cell movement.

Intermediate filaments

Provide mechanical support to cells.

Motor proteins

Proteins that move along microtubules.

Kinesins

Motor proteins moving toward microtubule plus end.

Dyneins

Motor proteins moving toward microtubule minus end.

Microtubule-organizing centers (MTOCs)

Sites where microtubules are nucleated and organized.

Protofilaments

Longitudinal rows of tubulin in microtubules.

α-tubulin

One subunit of the tubulin dimer.

β-tubulin

Other subunit of the tubulin dimer.

Plus end

End of microtubule with β-tubulin.

Minus end

End of microtubule with α-tubulin.

Microtubule-associated proteins (MAPs)

Proteins that stabilize and promote microtubule assembly.

Tau protein

MAP linked to Alzheimer's disease when hyperphosphorylated.

Cell shape

Determined by microtubule distribution and organization.

Cellular locomotion

Movement generated by cytoskeletal components.

Neurotransmitter transport

Movement of chemicals along nerve cell microtubules.

Lou Gehrig's disease

Neurological disease from microtubule transport defects.

Hydrolysis of ATP

Primary energy source for molecular motors.

Cell division machinery

Cytoskeletal components essential for cell division.

Mechanical support

Resisting forces that compress or bend fibers.

Radial array

Microtubule arrangement extending from the nucleus.

Kinesin

Microtubular motor moving toward plus end.

Dynein

Microtubular motor moving toward minus end.

Myosin

Motor protein that moves along actin filaments.

Cytoplasmic Dynein

Moves organelles and chromosomes during mitosis.

Kinesin Structure

Tetramer with two heavy and two light chains.

Kinesin Heads

Globular heads that bind microtubules and hydrolyze ATP.

Kinesin Tail

Fanlike structure that binds to cargo.

ATP Hydrolysis

Provides energy for motor protein activity.

Unidirectional Movement

Motor proteins move in one direction along tracks.

Conformational Changes

Alterations enabling mechanical cycles of motor proteins.

Processivity

Ability to move long distances without detaching.

Kinesin Cargo Transport

Transports vesicles outward to plasma membrane.