Cytoskeleton and Cell Movement - CH. 15 AI

Vocabulary flashcards covering key concepts related to the cytoskeleton, its functions, components, and mechanisms of action in cells.

Cytoskeleton

A network of proteins extending through cytoplasm and nucleus, giving structure, movement, adhesion, trafficking, and division.

Types of Cytoskeletal Filaments

Intermediate filaments, microtubules, and actin filaments.

Intermediate Filaments Function

Withstand mechanical stress and aid in cell adhesion.

Structure of Intermediate Filaments

Rope-like fibers; the most durable cytoskeletal elements.

Location of Intermediate Filaments

Throughout cytoplasm and inside the nucleus.

Proteins Forming Intermediate Filaments

A diverse family including keratins, neurofilaments, and lamins.

Nuclear Lamina

A meshwork of intermediate filaments beneath the nuclear envelope.

Keratin Filaments in Epithelial Cells

Provide mechanical strength by linking cells through desmosomes.

Consequences of Lacking Keratin Filaments

The sheet of cells would rupture when stretched.

Desmosomes

Junctions connecting keratin filaments of adjacent epithelial cells via cadherins.

Hemidesmosomes

Integrin-based junctions connecting keratin filaments to the basal lamina.

Defective Keratin Filaments Effects

Cells rupture between the nucleus and hemidesmosomes under minor trauma.

Keratin Gene Mutations Disease

Epidermolysis Bullosa Simplex (EBS).

EBS Dominance

Dominant.

What Happens in EBS?

Skin blisters due to basal cell lysis after minor stress.

Neurofilaments

Intermediate filaments in axons that provide mechanical strength.

Organization of Neurofilaments

Bundles cross-linked by proteins, greatly outnumbering microtubules.

Nuclear Lamina Composition

Lamin intermediate filaments.

Breakdown of Nuclear Lamina

Caused by phosphorylation of lamins by protein kinases.

Microtubules

Hollow cylinders that usually extend from a microtubule organizing center made of tubulin heterodimers.

Functions of Microtubules

Cell polarity, mitosis, cell extensions, movement, and intracellular traffic.

Number of Protofilaments in Microtubule

13 around a hollow center.

Tubulin Heterodimer Structure

An α-tubulin and β-tubulin pair.

Plus End of Tubulin

β-tubulin.

Binding Site for GTP/GDP on Tubulin

On β-tubulin.

Assembly Location of Microtubules

Mainly at their plus ends.

GTP Cap

A region of newly added GTP-tubulin that stabilizes microtubules.

Effect of High GTP-tubulin Concentration

Microtubules grow and maintain a GTP cap.

Effect of Low GTP-tubulin Concentration

Microtubules shrink (catastrophe).

Microtubules originate radially from a MTOC.

Microtubule organizing center.

Main MTOC in Animal Cells

The centrosome (pair of centrioles).

Orientation of Microtubule Plus Ends

Away from the MTOC.

During mitosis, microtubules form what.

Form the mitotic spindle.

Vesicle Transport Dependency

Motor proteins walk along them to move vesicles.

Major Motor Proteins on Microtubules

Kinesin and dynein.

Direction of Kinesin Movement

Toward the plus end.

Direction of Dynein Movement

Toward the minus end.

Main Function of Motor Proteins

ATP-dependent vesicle transport.

Motor Proteins' Role in Neurons

Transport synaptic vesicles down long axons.

Axoneme

The microtubule-based core of cilia and flagella.

Microtubule Arrangement in Axoneme

9 doublets + 2 central microtubules (9+2).

Dynein Movement in Axonemes

Their heads walk along adjacent B microtubules.

Prevention of Microtubule Sliding in Axonemes

Nexin cross-linking proteins.

Cause of Cilia/Flagella Bending

Dynein walking combined with nexin resistance.

Amoeboid Locomotion

Movement using actin polymerization at the leading edge.

Microtubules' Role in Amoeboid Locomotion

Deliver chemotactic receptors via vesicles.

Drug that Disrupts Microtubules

Colchicine.

Colchicine Treatment

Used to treat Gout.

Colchicine Mechanism

Binds free tubulin, preventing microtubule assembly.

Actin Filaments

Helical polymers of actin (microfilaments).

G-actin

Globular actin monomer that binds ATP/ADP.

F-actin

Filamentous actin—a double helix of G-actin chains.

Location of Actin Concentration

Beneath the plasma membrane.

Growth of Actin Filaments

ATP-bound G-actin adds to plus end; ADP-actin leaves minus end.

Actin Treadmilling

Plus-end growth with minus-end shrinkage, creating apparent movement.

Inducer of Actin Branching

The Arp2/3 complex.

Lamellipodia

Front extensions of migrating cells rich in branched actin.

Myosin I

Single-headed motor that moves vesicles or membrane along actin.

Myosin II

A two-headed motor forming bipolar thick filaments.

Sarcomere

The contractile unit of striated muscle.

Anchoring Structures for Actin Thin Filaments

Z-discs (plus ends attach).

Orientation of Actin in Sarcomeres

Minus ends toward the center, plus ends at Z-discs.

Cause of Muscle Contraction

Sliding of myosin-II thick filaments over actin.

Filament Length Change During Contraction

No, only overlap increases.

Trigger for Power Stroke

Release of Pi from myosin after binding actin.

Myosin Release from Actin Trigger

Binding of ATP.

Myosin Head Reset Mechanism

ATP hydrolysis into ADP + Pi (recovery stroke).