Cell Biology Cellular Movement - motility & contraction CONCEPT QUESTIONS
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What direction do kinesins move along microtubules?
Toward the plus (+) end.
What direction do dyneins move along microtubules?
Toward the minus (−) end.
What are the two types of dyneins?
Cytoplasmic dynein and axonemal (ciliary) dynein.
What type of motor protein moves along actin?
Myosin.
Why does a motor protein need a motor domain?
The motor domain binds to the cytoskeleton and powers movement using ATP hydrolysis.
How does ATP hydrolysis help a motor protein move?
It provides energy for conformational (shape) changes in the motor protein.
What is the role of the stalk and tail?
They contain the cargo-binding region, which allows the motor protein to attach to cargo.
What is the role of the neck region?
It acts like a lever that helps transmit movement from the motor domain.
What can light chains do?
They can help bind cargo or regulate the motor domain.
What parts of motor proteins can differ between different motor proteins?
The neck, stalk, and cargo-binding regions.
Why might different motor proteins have different neck, stalk, and cargo-binding regions?
These regions give motor proteins different structural and cargo-binding properties.
If two motor proteins have different structures but similar motor domains, what does that suggest?
Their motor domains perform a similar basic function, while their other regions give them different properties.
How does kinesin move along a microtubule?
It uses a hand-over-hand mechanism, where its two motor domains alternately step forward.
Why is kinesin movement called “processive”?
Because kinesin can take repeated steps along the microtubule without detaching.
What allows kinesin to move efficiently along microtubules?
Its hand-over-hand movement keeps at least one motor domain attached as it steps.
How does cytoplasmic dynein move along a microtubule?
Its motor domain rotates, causing the microtubule-binding stalk to pivot.
What role does the dynein stalk play in movement?
It binds the microtubule and pivots when the motor domain rotates.
Why are dynactin complexes important for dynein?
They connect dynein to different types of cargo.
How do motor proteins transport vesicles and organelles?
They move them along microtubules from a donor location to a target location.
Besides transporting cargo, what role do microtubules play in cells?
They help establish and maintain the location and organization of organelles.
What does the effect of nocodazole on the Golgi demonstrate?
Microtubules are important for establishing and/or maintaining Golgi structure.
What are cilia and flagella made of?
Microtubules organized into an axoneme and covered by the plasma membrane.
What is the main structural difference between cilia and flagella?
Cilia are shorter, while flagella are longer.
What is an axoneme?
The microtubule-based structure that makes up the core of cilia and flagella.
What structure is required for the formation of cilia and flagella?
A basal body, which is a centriole.
Why do cilia and flagella need microtubules?
Microtubules form their internal structure and allow them to function in movement
What is the basic structure of a centriole?
9 triplets of stable microtubules.
What is the basic structure of an axoneme?
9 microtubule doublets surrounding a central pair
How do centrioles and axonemes differ in their microtubule arrangement?
Centrioles have 9 triplets, while axonemes have 9 doublets + a central pair.
What important motor protein is found in the axoneme?
Axonemal dynein
How does axonemal dynein contribute to cilia movement?
It interacts with microtubules in the axoneme to produce movement.
What does dynein need to interact with to generate movement in the axoneme?
The microtubule doublets.
Why is axonemal dynein important for cilia and flagella?
Its activity produces the forces needed for their movement.
What type of cytoskeletal filament do actin motors interact with?
Actin filaments.
What is the main type of motor protein associated with actin?
Myosin.
How are actin motors different from kinesin and dynein?
Actin motors move along actin filaments, while kinesin and dynein move along microtubules.
What is the general purpose of actin motor proteins?
They use energy to produce movement along actin filaments.
What type of movement is skeletal muscle responsible for?
Contraction that produces movement of the body.
What role do actin and myosin play in skeletal muscle movement?
They interact to produce muscle contraction.
What type of motor protein is involved in skeletal muscle contraction?
Myosin.
How does myosin contribute to skeletal muscle movement?
Myosin interacts with actin to generate force and contraction.
What is a sarcomere?
The basic contractile unit of skeletal muscle.
What happens to sarcomeres during muscle contraction?
They shorten as the contractile filaments slide past each other.
Why are sarcomeres important for skeletal muscle movement?
Their shortening produces muscle contraction and movement.
How are sarcomeres organized in skeletal muscle?
They are arranged in repeating units along muscle fibers.
What are the two types of filaments found in a sarcomere?
Thick filaments and thin filaments.
What protein makes up the thick filaments?
Myosin
What protein makes up the thin filaments?
Actin.
How are thick and thin filaments related to muscle contraction?
They interact with each other to produce contraction.
Which filament contains the motor protein?
The thick filament contains myosin, the motor protein.
What does muscle contraction produce?
Tension.
What does “contraction = tension” mean?
Muscle contraction generates force/tension
What is the myosin cycle responsible for?
It produces movement of myosin along actin.
What molecule provides energy for the myosin cycle?
ATP
What happens to ATP during the myosin cycle?
ATP is hydrolyzed to provide energy for the cycle.
What two proteins interact during the myosin cycle?
Myosin and actin.
What is the overall result of the myosin cycle?
It generates force that contributes to muscle contraction.
What is the main process being regulated in muscle cells?
Muscle contraction.
Why does muscle contraction need to be regulated?
To control when contraction occurs and when the muscle remains relaxed.
What does regulation of contraction allow a muscle cell to control?
Whether contraction occurs and the level of contraction.
What is the overall purpose of the regulatory mechanisms involved in muscle contraction?
To control the activity that produces muscle tension.
What is the main process being regulated on this slide?
Muscle contraction.
What does regulation of muscle contraction determine?
Whether the muscle contracts and how contraction is controlled.
Why is regulation necessary for muscle contraction?
It allows contraction to be turned on and controlled rather than occurring continuously.
What is the overall role of regulatory mechanisms in muscle contraction?
They control the molecular interactions that produce muscle tension.
What is the sarcolemma?
The cell membrane of a muscle cell.
What is the sarcoplasmic reticulum?
A specialized membrane system in muscle cells involved in regulating contraction.
What two structures are highlighted on this slide in relation to muscle contraction?
The sarcolemma and the sarcoplasmic reticulum.
Why are the sarcolemma and sarcoplasmic reticulum important for muscle contraction?
They are involved in the processes that allow muscle cells to regulate contraction.
What is excitation-contraction coupling?
The process that connects excitation of a muscle cell to muscle contraction.
What does excitation-contraction coupling connect?
The electrical excitation of the muscle cell to the contraction of the muscle.
Why is excitation-contraction coupling important for muscle contraction?
It allows an electrical signal to trigger the processes that cause the muscle to contract.
What is the overall purpose of excitation-contraction coupling?
To convert a muscle cell’s excitation into contraction.
What type of muscle cells are introduced on slide 21?
Smooth muscle cells.
How are smooth muscle cells different from the skeletal muscle cells discussed earlier?
They are a different type of muscle cell with different structural and functional characteristics.
Why is smooth muscle important to study separately from skeletal muscle?
Smooth muscle uses different mechanisms to regulate contraction.
What process is being regulated in smooth muscle cells?
Smooth muscle contraction.
Why is regulation important for smooth muscle contraction?
It allows contraction to be controlled according to the needs of the muscle.
How does actin contribute to the movement of a migrating cell?
Actin polymerization at the leading edge extends the cell forward.
What is the role of new adhesions during cell migration?
New adhesions, anchored by actin, form underneath the lamellipodium and attach the cell to the substrate.
What happens at the trailing edge as the cell moves forward?
The trailing edge detaches and is pulled forward by contraction of the cell body.
What are the main steps involved in cell migration?
Actin polymerization extends the leading edge → new adhesions form → the trailing edge detaches and is pulled forward by contraction.