Microfilament-Based Motility: Muscle Contraction

Vesicle Transport

Movement of materials within the cell.

Phagocytosis

Cellular process of engulfing particles.

Microfilament-Based Motility

Movement driven by actin microfilaments and myosins.

Myosins

ATP-dependent motors that interact with actin filaments.

Skeletal Muscle

Striated muscle responsible for voluntary movements.

Smooth Muscle

Non-striated muscle controlling involuntary movements.

ATP Hydrolysis

Process providing energy for myosin movement.

Type II Myosins

Best understood myosins, involved in muscle contraction.

Thick Filaments

Composed of myosin, involved in muscle contraction.

Thin Filaments

Contain actin, tropomyosin, and troponin proteins.

Sarcomere

Repeating unit of muscle fibers, defined by Z lines.

A Bands

Dark bands in muscle fibers, containing thick filaments.

I Bands

Light bands in muscle fibers, containing thin filaments.

Z Line

Dense structure marking boundaries of sarcomeres.

Cross-Bridges

Temporary connections between myosin heads and actin.

Sliding-Filament Model

Explains muscle contraction through filament sliding.

Calcium's Role

Regulates myosin-binding sites on actin filaments.

Troponin

Calcium-sensitive protein regulating myosin access to actin.

Tropomyosin

Protein blocking myosin-binding sites on actin.

Power Stroke

Myosin head movement pulling actin filaments during contraction.

Contraction Cycle

Sequence of events during muscle contraction involving myosin.

Cocking of Myosin Head

Repositioning of myosin head after ATP hydrolysis.

Actin Microfilaments

Filaments providing structure and motility in cells.

Myofibrils

Bundles of filaments within muscle fibers.

Regulatory Light Chains

Control myosin activity and ATPase function.

Essential Light Chains

Support myosin structure and function.

Calcium Concentration

Influences muscle contraction and relaxation states.

Force Generation

Depends on actin-binding domain interactions during contraction.

Nerve Impulses

Activate muscle cells for contraction.

Calcium Levels

Regulate contraction and relaxation in muscles.

Acetylcholine

Neurotransmitter that opens Na+ channels.

Depolarization

Change in membrane potential due to Na+ influx.

Voltage-Gated Ca2+ Channels

Open in response to depolarization, allowing Ca2+ influx.

Ryanodine Receptors

Stimulated by Ca2+, release Ca2+ from sarcoplasmic reticulum.

Sarcoplasmic Reticulum

Calcium storage organelle in muscle cells.

ATP-Dependent Ca2+ Pumps

Remove Ca2+ from sarcoplasm during relaxation.

Smooth Muscle

Involuntary muscle with slower contractions.

Dense Bodies

Anchors for actin and myosin in smooth muscle.

Calmodulin

Calcium-binding protein activating MLCK in smooth muscle.

Myosin Light-Chain Kinase (MLCK)

Phosphorylates myosin light chains for contraction.

Myosin Light-Chain Phosphorylation

Activates myosin for interaction with actin.

Cross-Bridge Cycle

Process of myosin binding to actin for contraction.

Myosin Light-Chain Phosphatase

Removes phosphate, leading to muscle relaxation.

Calcium Concentration Increase

Triggers contraction cascade in smooth muscle.

Contraction Duration

Smooth muscle contractions are longer than skeletal muscle.

Skeletal Muscle

Striated muscle responsible for voluntary movements.

Calcium Binding Partners

Different in skeletal versus smooth muscle cells.

Contraction Mechanism

Both muscle types utilize Ca2+ for contraction.