Chapter 14: Cellular Movement: Motility & Contractility

These flashcards cover key vocabulary terms related to cellular movement, motor proteins, and muscle contraction, providing definitions and essential concepts from the lecture.

Microtubule associated motor proteins

Motor proteins that move cargo along the cytoskeletal tracks. (mechanoenzymes)

Microfilaments

are actin protein filaments that provide structural support and enable cellular movement.

microtubules

are cylindrical structures made of tubulin proteins that are critical for maintaining cell shape, providing tracks for motor proteins, and facilitating cell division.

Motor Proteins

are proteins that convert chemical energy into mechanical work, facilitating movement along cytoskeletal filaments.

Cytoskeleton

Network of filaments and tubules in the cytoplasm, essential for cell movement and shape.

Kinesin

A microtubule motor protein that moves towards the plus (+) end of the microtubule. (away from cell center)

Kinesin structure

two intertwined heavy chains; two globular heads at on end; tail region that binds to cargo

Globular heads

Bind to B-tubilin subunits on microtubules; hydrolyze ATP to facilitate movement along the microtubule.

Steps of ATP hydrolysis

• one foot binds to the microtubule, causing a conformational change that moves the other foot forward. 

• atp binds to the leading head, inducing a conformational change that allows it to release from the microtubule. Subsequent hydrolysis of ATP then triggers the movement of the trailing head forward.

• This process repeats, allowing kinesin to travel along the microtubule towards the plus end.

Dynein

A larger, more complex motor protein that moves toward the minus (-) end of microtubules.

cannot bind directly to cargo but associates with dynactin complex for cargo transport.

Cilia

Short hair-like structures that move fluids across cell surfaces or propel cells.

100’s per cell

Flagella

Long whip-like or undulating motion structures that propel cells through fluids.

One or few per cell

Doublets

pairs of microtubules that make up the axoneme structure in cilia and flagella, providing structural support and enabling movement.

They consist of two fused microtubules and assist in the beating motion essential for motility.

They are typically arranged in a 9 + 2 formation, which is crucial for the function of cilia and flagella.

Axoneme structure

The central strand of a cilium or flagellum, composed of microtubule doublets and essential for movement.

It provides the structural framework that enables the bending and beating of cilia and flagella.

Base of cilium or flagellum

The region where the cilium or flagellum is anchored to the cell, typically containing a microtubule organizing center.

Basal body structurally similar to centriole

Myosins

Motor proteins that interact with actin filaments to generate movement inside cells.

Myosin structure

A protein structure composed of heavy and light chains that forms the motor domain for interaction with actin.

Globular heads of myosin

The portions of myosin molecules that bind to actin filaments and produce force during muscle contraction or cellular movement.

Use ATP to drive conformational changes necessary for movement.

Major types of Myosin

Include Myosin I, II, and V, each with distinct roles in cellular processes such as muscle contraction, cargo transport, and cell motility.

Myosin I

A type of myosin involved in intracellular transport and movement, often associated with vesicles and organelles.

Myosin II

A type of myosin primarily responsible for muscle contraction and contractility in muscle cells, it forms filaments that interact with actin to generate force.

Myosin V

A type of myosin involved in transporting cargo along actin filaments, particularly in neurons and other cells, by moving vesicles and organelles.

Myosin VI

A type of myosin that plays a role in endocytosis and organelle transport, moving cargo towards the minus end of actin filaments.

Griscelli’s Disease

A rare genetic disorder characterized by immunodeficiency and neurological complications, caused by mutations affecting myosin motor proteins, leading to issues with pigment transport in cells.

Myosin V mutation

• silvery hair

• secretory vesicles in T-cells are impaired resulting in neurological problems and immunodeficiency. 

Situs inversum viscerum

A condition where internal organs are reversed or mirrored from their usual positions, often associated with abnormalities in ciliary movement. (embryonic development disorder)

Ushers syndrome

A genetic disorder characterized by hearing loss and progressive vision loss due to retinal degeneration, caused by mutations in genes essential for sensory function.

Sarcolemma

The plasma membrane which encloses a striated muscle fiber and plays a key role in muscle contraction and signal transduction.

ATP hydrolysis

Chemical reaction that releases energy by breaking down ATP, fueling movements in motor proteins.

Basal body

Structure that anchors cilia and flagella; similar to a centriole with a 9 triplet microtubule arrangement.

Sarcoplasmic reticulum

Specialized endoplasmic reticulum in muscle cells that stores calcium ions; myofybrils are surrounded by this structure and play a crucial role in muscle contraction by regulating calcium release.

T-tubules

Transverse tubules that help carry electrical signals into the muscle cell interior; connect cell membrane with SR and help carry electrical signals into the cell interior

Sliding filament theory

Theory that explains muscle contraction by the sliding action of actin and myosin filaments.

when does muscle contraction occur?

Muscle contraction occurs when calcium ions are released from the sarcoplasmic reticulum, allowing actin and myosin filaments to slide past each other. Thin filaments slide past thick filaments to shorten the muscle fiber.

Troponin

Long thin protein that winds around actin in muscle fibers; blocks myosin binding sites on actin when the muscle is relaxed; Protein that binds calcium and regulates the binding of myosin to actin in muscle contraction.

Tropomyosin

Protein that blocks myosin-binding sites on actin filaments in a relaxed muscle.

Steps of muscle contraction

Step 1: a motor neuron’s axon terminals contain vesicles filled with neurotransmitter acetylcholine that is released into the neuromuscular junction, triggering an action potential in the muscle fiber; when nerve signal reaches the terminal ACh is released into the synaptic cleft

Step 2 muscle contraction

Calcium ions are released from the sarcoplasmic reticulum, binding to troponin, causing tropomyosin to move and expose myosin-binding sites on actin.

Step 3 of muscle contraction

Binding opens Na+ channels allowing sodium to enter the muscle fiber and depolarize the membrane (muscle less negative); the electrical change initiates the signal that spreads across the sarcolema and down into the T-tubules

Step 4 of muscle contraction 

Z line

Dark zig-zag lines that marks the ends of a sarcomere and anchors + ends of actin filaments;

Cap z

a protein that caps the plus ends of actin filaments, stabilizing them and preventing further growth.

Nebulin

a large actin-binding protein that helps regulate the length of thin filaments in skeletal muscle and contributes to sarcomere structure; helps stabile actin filaments and determine exact length

M line

the middle line of a sarcomere that anchors thick filaments (myosin) and maintains alignment between the filaments; inside A band; anchors thick myosin filaments; contains protein like myomesin and M-protein in order to stabilize

A band

where actin and myosin overlap with eachother

I band

contains only actin- thin filaments (no myosin) on either side of Z line; during contraction the I bands shorten

Neuromuscular junction

The synapse where a motor neuron communicates with a muscle fiber.

Acetylcholine (ACh)

Neurotransmitter released at the neuromuscular junction to stimulate muscle contraction.

Myofibrils

Contractile fibers within muscle cells that are responsible for muscle contraction.