L13: Moving Cargo in the Cell Flashcards
What are motor proteins?
Enzymes that convert chemical energy, like ATP, into mechanical energy to produce movement within the cell.
What are the two main types of motor proteins involved in intracellular transport?
Myosin’s, which move along actin filaments, and kinesins and dynein’s, which move along microtubules.
What are the three main structural parts of myosin proteins?
Head domain (binds to actin and hydrolyses ATP), neck domain (acts as a lever for movement), and tail domain (varies and interacts with cargo).
What is the main function of kinesins?
Kinesins move cargo toward the plus end of microtubules, usually toward the cell periphery.
How does dynein differ from kinesin in terms of directionality?
Dynein’s move cargo toward the minus end of microtubules, typically toward the cell centre.
What is the role of ATP in motor protein function?
ATP hydrolysis drives conformational changes in motor proteins, enabling them to move along cytoskeletal filaments.
What is a ‘non-processive’ motor protein?
A motor that does not coordinate its heads and may detach from the filament intermittently, such as myosin in muscle contraction.
What is a ‘processive’ motor protein?
A motor that coordinates its heads to stay attached to the filament continuously, allowing smooth movement, as seen with kinesin and some myosin’s.
How is cargo transported along microtubules in neurons?
Kinesins carry materials to the synapse along microtubules, while dynein’s return materials to the cell body.
What is cytokinesis, and how do motor proteins assist in this process?
Cytokinesis is the division of the cell’s cytoplasm, during which motor proteins and actin filaments form a contractile ring that pinches the cell into two daughter cells.
What is the myosin superfamily, and how many types are there?
The myosin superfamily consists of around 16 different types of myosin’s, each specialized for various functions, including muscle contraction and intracellular transport.
What happens when ATP binds to the myosin head?
ATP binding causes the myosin head to release from the actin filament, initiating a conformational change that leads to movement.
What is the ‘power stroke’ in myosin movement?
The power stroke is the phase in which the myosin head binds to actin, releases ADP, and returns to its original conformation, pulling the actin filament along.
How do different lengths of the myosin neck domain affect movement speed?
Longer neck domains in myosin’s allow for larger steps and faster movement along actin filaments.
Which myosin type is known to move in the opposite direction on actin filaments compared to other myosin’s?
Myosin VI is unique as it moves toward the minus end of actin filaments, unlike most other myosin’s that move toward the plus end.
What is the function of kinesin spindle proteins during cell division?
Kinesin spindle protein assembly help segregate chromosomes by moving them along microtubules during mitosis.
What structural similarity does kinesins and myosin’s share despite low sequence homology?
Both have a conserved head domain for filament binding and ATP hydrolysis, a neck domain for movement, and a tail domain for cargo binding.
How does phosphorylation regulate myosin activity?
Phosphorylation of myosin light chains can activate myosin by enabling it to form filaments and interact with actin, leading to contraction.
What is dynein’s role in the movement of cilia and flagella?
Axonemal dynein’s slide microtubules against each other to create the bending motion that powers the beating of cilia and flagella.
What distinguishes cytoplasmic dynein from axonemal dynein?
Cytoplasmic dynein transports organelles and vesicles along microtubules, while axonemal dynein is involved in the movement of cilia and flagella.
How do dynein and kinesin coordinate cargo transport within the cell?
Kinesins typically transport cargo toward the cell periphery (plus end of microtubules), while dynein’s bring cargo back toward the cell centre (minus end).
How is directionality determined for kinesin movement along microtubules?
The location of the kinesin motor domain determines directionality, with most kinesins moving toward the plus end of microtubules.
What is the significance of motor proteins in immune defence and wound healing?
Motor proteins aid in cell movement necessary for immune cells to reach infection sites and for cells to migrate during wound healing.
Why are kinesins considered processive motors?
Kinesins work by coordinating two heads that alternately bind and release from microtubules, enabling continuous movement without detaching.
How does ATP hydrolysis drive conformational changes in motor proteins?
ATP hydrolysis causes a conformational change in the motor protein’s structure, which is then transmitted as movement along cytoskeletal filaments.
What are microtubules, and what is their role in intracellular transport?
Microtubules are structural filaments that serve as ‘tracks’ for motor proteins like kinesins and dynein’s to transport cargo across the cell.
What experimental technique helped to understand motor protein function?
In vitro motility assays, where motor proteins or their fragments are placed on glass surfaces with labelled filaments to observe movement in the presence of ATP.
How does kinesin coordinate movement along microtubules?
Kinesin’s two heads work in a hand-over-hand manner, with one head always attached to the microtubule while the other moves forward.
What is the function of myosin II in muscle cells?
Myosin II enables muscle contraction by forming thick filaments that pull on actin filaments, causing shortening of the muscle fibre.
What is the role of the ‘tail domain’ in motor proteins?
The tail domain binds to specific cargo, allowing the motor protein to transport various vesicles, organelles, or other cellular materials.
Why is the actin-myosin interaction referred to as a ‘cross-bridge cycle’?
Because myosin heads cyclically attach to and detach from actin filaments in a process that generates movement through ATP hydrolysis.
What types of movements do myosin’s facilitate besides muscle contraction?
Myosin’s also facilitate intracellular cargo transport, cellular shape changes, and vesicle transport over short distances.
What is the structure of a typical kinesin molecule?
A kinesin molecule has two heavy chains with globular heads that bind microtubules, a neck linker for movement, and a tail domain that binds cargo.
What is the significance of ‘plus’ and ‘minus’ ends in microtubules?
These ends determine the directionality of motor protein movement, with kinesins generally moving toward the plus end and dynein’s toward the minus end.
What is the role of dynein’s in the mitotic spindle?
Dynein’s help to position and separate chromosomes by moving along microtubules in the spindle apparatus during cell division.
How do motor proteins contribute to cell shape and structure?
They transport and arrange cytoskeletal components and organelles, helping the cell adapt its shape in response to environmental needs.
How does the length of the neck domain influence myosin function?
A longer neck domain allows for a larger step size, increasing the speed of myosin movement along actin filaments.
What is the function of actin filaments in cells?
Actin filaments provide structural support, enable cellular movement, and serve as tracks for myosin motor proteins.
How do motor proteins ensure directional movement within cells?
Motor proteins have inherent directionality toward either the plus or minus end of filaments, ensuring targeted transport within cells.
What roles do phosphorylation and dephosphorylation play in motor protein regulation?
Phosphorylation activates or deactivates motor proteins, allowing them to function only when and where needed.
What allows kinesins and dynein’s to move distinct cargoes to different cellular locations?
The diversity in tail domains allows these proteins to bind to specific cargoes and transport them to designated cell regions.
How do myosin motor proteins aid in cytokinesis?
Myosin motors form a contractile ring with actin filaments at the division site, pulling the membrane inward to split the cell.
What is a ‘conventional kinesin’?
Conventional kinesins are primarily involved in transporting vesicles and organelles along microtubules toward the cell periphery.
What is a ‘power stroke’ in the dynein motor mechanism?
It is the movement generated by ATP hydrolysis, causing a conformational change that moves the dynein along the microtubule.
Why are axonal transport systems critical for neurons?
They move materials efficiently across the long distances of axons, ensuring delivery of essential proteins and organelles to the synapse.
