Notes 3: Cell Motility and Contraction

cell shape, functional

• Role of Actin Filaments

  • Regulation of ___ ___: Actin filaments control cellular morphology.

  • ___ Diversity: Actin involved in various cellular processes.

microvilli, muscle, moving, division

• Role of Actin Filaments

  • Examples:

    • ____: Extensions of intestinal cells aiding nutrient absorption.

    • ___ Cells: Actin filaments contribute to cell contraction.

    • ___ Cells: Actin filaments present at the leading edge.

    • Cell ____: Form temporary circular rings during division.

nutrient, contraction, leading, rings

• Significance of Actin:

  • Microvilli: Aid in ____ absorption in intestinal cells.

  • Muscle Contraction: Actin filaments crucial for cell ____.

  • Cell Movement: Actin present at ___ edge of moving cells.

  • Cell Division: Actin forms temporary ___, aiding in division.

single, dimers, tubulin, protofilaments

• Differences Between Actin Filaments and Microtubules

  • Structure:

    • Actin filaments: ___ filaments composed of actin ___.

    • Microtubules: Tubular structure formed by ___ dimers organized into ___.

ATPases, ATP, GTPases, GTP

• Differences Between Actin Filaments and Microtubules

  • Dimers:

    • Actin: ____; use ___ for polymerization.

    • Microtubules: ____; use ___ for polymerization.

plus, minus, plus

• Differences Between Actin Filaments and Microtubules

  • Directionality:

    • Actin: Grow towards the ___ end, shrink towards the ___ end.

    • Microtubules: Grow and shrink at the ___ end.

independently, centrosome

• Differences Between Actin Filaments and Microtubules

  • Anchoring:

    • Actin: Not anchored to a center; grow and shrink ______.

    • Microtubules: Anchored to the ___; grow towards the plus end.

cortical actin, cortex

• Cell Movement

• Cell Movement Mechanism

  • Leading Edge:

    • Formed by ___ __ underneath the plasma membrane.

    • ___ envelopes the cell.

actin, myosin

• Cell Movement

• Cell Movement Process:

  • Leading edge grows towards a direction, stretching the cell.

  • At the opposite end:

    • ___ depolymerizes.

    • ____ contracts.

lamellipodium, calcium, heterodimers

• Cell Movement

• Interaction with Extracellular Matrix:

  • ____ attached to substratum via integrins.

  • Integrins require ___ for interaction.

  • Integrins are _____.

Lamellipodium, Cortical actin, Contraction, attachment

• Cell Movement

• Cycle of Movement:

  • _____ attaches to substratum.

  • _____ ____ grows and detaches.

  • _____ at opposite end moves the cell forward.

  • New ____ forms, and the process repeats.

actin

• Actin-Related Proteins (ARPs)

  • Role in Cell Movement:

    • Assist in the organization and function of ___ filaments.

mesh, electron

ARPs

• Cortical Actin:

  • Forms ___ underneath the plasma membrane.

  • Visible in ___ micrographs.

Lamellipodium

ARPs

• Cell Movement Observation:

  • Fish skin cell moving across the field of view.

  • ___ pulls the cell forward.

capping, shrinks

• Stabilization of Actin Filaments at Leading Edge:

  • Plus End: Stabilized by ___ proteins.

  • Minus End: Actin ___.

globular, linear, dimers, tail

• Myosins: Motor Proteins

  • Structure:

    • ____ head and ___ tail.

    • Typically exist as ___.

    • ___ dimerizes.

actin, cargo

• Myosins: Motor Proteins

  • Function:

    • Head interacts with ___.

    • Tail interacts with ___.

plus

• Myosins: Motor Proteins

  • Movement:

    • Towards the __ end of actin.

muscle, thick

• Special Structural Organization of Muscle-Specific Myosins

  • Dimerization:

    • Myosins always dimerized in ___ cells.

    • ____ filaments formed in skeletal and cardiac muscle cells.

tails, heads, tail, tail, bundle, structural

• Special Structural Organization of Muscle-Specific Myosins

• Organization:

  • Dimer with dimerized __ and two _.

  • Multiple dimers organize ___ to ___.

  • Forms a ___ with strong structural organization.

bundle, tails, heads

• Special Structural Organization of Muscle-Specific Myosins

• Structural Formation:

  • Coiled-Coil Dimers:

    • Heads and tails arranged in a ___.

    • Central region with ___ and peripheral region with multiple ___.

actin, myosin, interface

Anatomical Structure of Muscle Cells and Sarcomere

• Thin Filament (___): Represented in red.

• Thick Filament (____): Represented in green.

• ____: Where myosin heads interact with actin.

minus, capping

Anatomical Structure of Muscle Cells and Sarcomere

• Z Disc:

  • Binds the ___ ends of actin filaments.

  • Contains ____ protein, including Titan.

Titan, Z disc

Anatomical Structure of Muscle Cells and Sarcomere

• ____ Protein:

  • Enormous protein.

  • Main component of __ __.

myosin, actin, myosin, actin

Anatomical Structure of Muscle Cells and Sarcomere

• Striations:

  • Dark regions: ___.

  • Very dark: Both ___ and ___.

  • Light regions: ___.

Z disc, striations

Anatomical Structure of Muscle Cells and Sarcomere

• Structural Significance:

  • _ _ maintains sarcomere integrity.

  • _____ result from the arrangement of myosin and actin filaments.

stimulation, Action Potential, calcium release,

Muscle Contraction Mechanism

• _______: Neuron activates muscle cell.

• ________ ______: Spreads over muscle cell membrane.

• ________ _____: Triggered by action potential.

T-tubules

Muscle Contraction Mechanism

• Cell Architecture:

  • __-__ distribute calcium throughout cytosol.

Sarcoplasmic Reticulum

_________ ________ (SR): Major calcium store in muscle cells.

myofibril, actin, myosin, tropomyosin, troponin, motors

• Contraction Process:

  • Calcium interacts with protein filaments in ____.

  • Calcium triggers interaction between ___ and ___ filaments.

  • ____ moves off myosin binding sites on actin.

  • ___ binds to calcium, facilitating tropomyosin movement.

  • Myosin ___ interact with actin, causing muscle fiber contraction.

Calcium Reabsorption:

Muscle Contraction

______ ____: Pump returns calcium to sarcoplasmic reticulum

relaxation

Muscle Contraction

______: Without calcium, myosin releases actin and filaments slide back.

Tropomyosin, Binding, Hydrolysis, Actin, Sliding, Contraction, Relaxation

• Steps of Muscle Contraction

  • 1. ____ Movement:

  • 2. ATP ____:

  • 3. ATP _____:

  • 4. Binding to ___:

  • 5. ____ Movement:

  • 6. ___ and ___:

troponin, actin, myosin

• Steps of Muscle Contraction

  • 1. Tropomyosin Movement:

    • ___ bound to calcium undergoes conformational change.

    • Moves away, allowing ___ and ___ interaction.

  • 2. ATP Binding:

    • ATP binds to myosin head.

    • Myosin head becomes bound to ATP.

  • 3. ATP Hydrolysis:

    • ATP hydrolysis occurs.

    • Myosin head moves, bound to ADP and phosphate.

  • 4. Binding to Actin:

    • Myosin head binds to actin.

    • Detaches and binds ATP again.

  • 5. Sliding Movement:

    • Myosin slides along actin filament.

    • Sarcomere contracts as myosin moves.

  • 6. Contraction and Relaxation:

    • Cycle repeats until calcium is depleted.

    • Resulting in muscle contraction and relaxation.

myosin, ATP

• Steps of Muscle Contraction

  • 1. Tropomyosin Movement:

    • Troponin bound to calcium undergoes conformational change.

    • Moves away, allowing actin and myosin interaction.

  • 2. ATP Binding:

    • ATP binds to ___ head.

    • Myosin head becomes bound to ___.

  • 3. ATP Hydrolysis:

    • ATP hydrolysis occurs.

    • Myosin head moves, bound to ADP and phosphate.

  • 4. Binding to Actin:

    • Myosin head binds to actin.

    • Detaches and binds ATP again.

  • 5. Sliding Movement:

    • Myosin slides along actin filament.

    • Sarcomere contracts as myosin moves.

  • 6. Contraction and Relaxation:

    • Cycle repeats until calcium is depleted.

    • Resulting in muscle contraction and relaxation.

hydrolysis, myosin, ADP, phosphate

• Steps of Muscle Contraction

  • 1. Tropomyosin Movement:

    • Troponin bound to calcium undergoes conformational change.

    • Moves away, allowing actin and myosin interaction.

  • 2. ATP Binding:

    • ATP binds to myosin head.

    • Myosin head becomes bound to ATP.

  • 3. ATP Hydrolysis:

    • ATP ____ occurs.

    • ___ head moves, bound to ___ and ___.

  • 4. Binding to Actin:

    • Myosin head binds to actin.

    • Detaches and binds ATP again.

  • 5. Sliding Movement:

    • Myosin slides along actin filament.

    • Sarcomere contracts as myosin moves.

  • 6. Contraction and Relaxation:

    • Cycle repeats until calcium is depleted.

    • Resulting in muscle contraction and relaxation.

myosin, ATP

• Steps of Muscle Contraction

  • 1. Tropomyosin Movement:

    • Troponin bound to calcium undergoes conformational change.

    • Moves away, allowing actin and myosin interaction.

  • 2. ATP Binding:

    • ATP binds to myosin head.

    • Myosin head becomes bound to ATP.

  • 3. ATP Hydrolysis:

    • ATP hydrolysis occurs.

    • Myosin head moves, bound to ADP and phosphate.

  • 4. Binding to Actin:

    • ___ head binds to actin.

    • Detaches and binds ___ again.

  • 5. Sliding Movement:

    • Myosin slides along actin filament.

    • Sarcomere contracts as myosin moves.

  • 6. Contraction and Relaxation:

    • Cycle repeats until calcium is depleted.

    • Resulting in muscle contraction and relaxation.

actin, sarcomere

• Steps of Muscle Contraction

  • 1. Tropomyosin Movement:

    • Troponin bound to calcium undergoes conformational change.

    • Moves away, allowing actin and myosin interaction.

  • 2. ATP Binding:

    • ATP binds to myosin head.

    • Myosin head becomes bound to ATP.

  • 3. ATP Hydrolysis:

    • ATP hydrolysis occurs.

    • Myosin head moves, bound to ADP and phosphate.

  • 4. Binding to Actin:

    • Myosin head binds to actin.

    • Detaches and binds ATP again.

  • 5. Sliding Movement:

    • Myosin slides along ___ filament.

    • ____ contracts as myosin moves.

  • 6. Contraction and Relaxation:

    • Cycle repeats until calcium is depleted.

    • Resulting in muscle contraction and relaxation.

calcium, relaxation

• Steps of Muscle Contraction

  • 1. Tropomyosin Movement:

    • Troponin bound to calcium undergoes conformational change.

    • Moves away, allowing actin and myosin interaction.

  • 2. ATP Binding:

    • ATP binds to myosin head.

    • Myosin head becomes bound to ATP.

  • 3. ATP Hydrolysis:

    • ATP hydrolysis occurs.

    • Myosin head moves, bound to ADP and phosphate.

  • 4. Binding to Actin:

    • Myosin head binds to actin.

    • Detaches and binds ATP again.

  • 5. Sliding Movement:

    • Myosin slides along actin filament.

    • Sarcomere contracts as myosin moves.

  • 6. Contraction and Relaxation:

    • Cycle repeats until ___ is depleted.

    • Resulting in muscle contraction and ___.