L13: Moving Cargo in the Cell

Question 1

What are motor proteins?

Answer 1

Enzymes that convert chemical energy, like ATP, into mechanical energy to produce movement within the cell.

Question 2

What are the two main types of motor proteins involved in intracellular transport?

Answer 2

Myosin’s, which move along actin filaments, and kinesins and dynein’s, which move along microtubules.

Question 3

What are the three main structural parts of myosin proteins?

Answer 3

Head domain (binds to actin and hydrolyses ATP), neck domain (acts as a lever for movement), and tail domain (varies and interacts with cargo).

Question 4

What is the main function of kinesins?

Answer 4

Kinesins move cargo toward the plus end of microtubules, usually toward the cell periphery.

Question 5

How does dynein differ from kinesin in terms of directionality?

Answer 5

Dynein’s move cargo toward the minus end of microtubules, typically toward the cell centre.

Question 6

What is the role of ATP in motor protein function?

Answer 6

ATP hydrolysis drives conformational changes in motor proteins, enabling them to move along cytoskeletal filaments.

Question 7

What is a ‘non-processive’ motor protein?

Answer 7

A motor that does not coordinate its heads and may detach from the filament intermittently, such as myosin in muscle contraction.

Question 8

What is a ‘processive’ motor protein?

Answer 8

A motor that coordinates its heads to stay attached to the filament continuously, allowing smooth movement, as seen with kinesin and some myosin’s.

Question 9

How is cargo transported along microtubules in neurons?

Answer 9

Kinesins carry materials to the synapse along microtubules, while dynein’s return materials to the cell body.

Question 10

What is cytokinesis, and how do motor proteins assist in this process?

Answer 10

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.

Question 11

What is the myosin superfamily, and how many types are there?

Answer 11

The myosin superfamily consists of around 16 different types of myosin’s, each specialized for various functions, including muscle contraction and intracellular transport.

Question 12

What happens when ATP binds to the myosin head?

Answer 12

ATP binding causes the myosin head to release from the actin filament, initiating a conformational change that leads to movement.

Question 13

What is the ‘power stroke’ in myosin movement?

Answer 13

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.

Question 14

How do different lengths of the myosin neck domain affect movement speed?

Answer 14

Longer neck domains in myosin’s allow for larger steps and faster movement along actin filaments.

Question 15

Which myosin type is known to move in the opposite direction on actin filaments compared to other myosin’s?

Answer 15

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.

Question 16

What is the function of kinesin spindle proteins during cell division?

Answer 16

Kinesin spindle protein assembly help segregate chromosomes by moving them along microtubules during mitosis.

Question 17

What structural similarity does kinesins and myosin’s share despite low sequence homology?

Answer 17

Both have a conserved head domain for filament binding and ATP hydrolysis, a neck domain for movement, and a tail domain for cargo binding.

Question 18

How does phosphorylation regulate myosin activity?

Answer 18

Phosphorylation of myosin light chains can activate myosin by enabling it to form filaments and interact with actin, leading to contraction.

Question 19

What is dynein’s role in the movement of cilia and flagella?

Answer 19

Axonemal dynein’s slide microtubules against each other to create the bending motion that powers the beating of cilia and flagella.

Question 20

What distinguishes cytoplasmic dynein from axonemal dynein?

Answer 20

Cytoplasmic dynein transports organelles and vesicles along microtubules, while axonemal dynein is involved in the movement of cilia and flagella.

Question 21

How do dynein and kinesin coordinate cargo transport within the cell?

Answer 21

Kinesins typically transport cargo toward the cell periphery (plus end of microtubules), while dynein’s bring cargo back toward the cell centre (minus end).

Question 22

How is directionality determined for kinesin movement along microtubules?

Answer 22

The location of the kinesin motor domain determines directionality, with most kinesins moving toward the plus end of microtubules.

Question 23

What is the significance of motor proteins in immune defence and wound healing?

Answer 23

Motor proteins aid in cell movement necessary for immune cells to reach infection sites and for cells to migrate during wound healing.

Question 24

Why are kinesins considered processive motors?

Answer 24

Kinesins work by coordinating two heads that alternately bind and release from microtubules, enabling continuous movement without detaching.

Question 25

How does ATP hydrolysis drive conformational changes in motor proteins?

Answer 25

ATP hydrolysis causes a conformational change in the motor protein's structure, which is then transmitted as movement along cytoskeletal filaments.

Question 26

What are microtubules, and what is their role in intracellular transport?

Answer 26

Microtubules are structural filaments that serve as 'tracks' for motor proteins like kinesins and dynein’s to transport cargo across the cell.

Question 27

What experimental technique helped to understand motor protein function?

Answer 27

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.

Question 28

How does kinesin coordinate movement along microtubules?

Answer 28

Kinesin's two heads work in a hand-over-hand manner, with one head always attached to the microtubule while the other moves forward.

Question 29

What is the function of myosin II in muscle cells?

Answer 29

Myosin II enables muscle contraction by forming thick filaments that pull on actin filaments, causing shortening of the muscle fibre.

Question 30

What is the role of the 'tail domain' in motor proteins?

Answer 30

The tail domain binds to specific cargo, allowing the motor protein to transport various vesicles, organelles, or other cellular materials.

Question 31

Why is the actin-myosin interaction referred to as a 'cross-bridge cycle'?

Answer 31

Because myosin heads cyclically attach to and detach from actin filaments in a process that generates movement through ATP hydrolysis.

Question 32

What types of movements do myosin’s facilitate besides muscle contraction?

Answer 32

Myosin’s also facilitate intracellular cargo transport, cellular shape changes, and vesicle transport over short distances.

Question 33

What is the structure of a typical kinesin molecule?

Answer 33

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.

Question 34

What is the significance of 'plus' and 'minus' ends in microtubules?

Answer 34

These ends determine the directionality of motor protein movement, with kinesins generally moving toward the plus end and dynein’s toward the minus end.

Question 35

What is the role of dynein’s in the mitotic spindle?

Answer 35

Dynein’s help to position and separate chromosomes by moving along microtubules in the spindle apparatus during cell division.

Question 36

How do motor proteins contribute to cell shape and structure?

Answer 36

They transport and arrange cytoskeletal components and organelles, helping the cell adapt its shape in response to environmental needs.

Question 37

How does the length of the neck domain influence myosin function?

Answer 37

A longer neck domain allows for a larger step size, increasing the speed of myosin movement along actin filaments.

Question 38

What is the function of actin filaments in cells?

Answer 38

Actin filaments provide structural support, enable cellular movement, and serve as tracks for myosin motor proteins.

Question 39

How do motor proteins ensure directional movement within cells?

Answer 39

Motor proteins have inherent directionality toward either the plus or minus end of filaments, ensuring targeted transport within cells.

Question 40

What roles do phosphorylation and dephosphorylation play in motor protein regulation?

Answer 40

Phosphorylation activates or deactivates motor proteins, allowing them to function only when and where needed.

Question 41

What allows kinesins and dynein’s to move distinct cargoes to different cellular locations?

Answer 41

The diversity in tail domains allows these proteins to bind to specific cargoes and transport them to designated cell regions.

Question 42

How do myosin motor proteins aid in cytokinesis?

Answer 42

Myosin motors form a contractile ring with actin filaments at the division site, pulling the membrane inward to split the cell.

Question 43

What is a 'conventional kinesin'?

Answer 43

Conventional kinesins are primarily involved in transporting vesicles and organelles along microtubules toward the cell periphery.

Question 44

What is a 'power stroke' in the dynein motor mechanism?

Answer 44

It is the movement generated by ATP hydrolysis, causing a conformational change that moves the dynein along the microtubule.

Question 45

Why are axonal transport systems critical for neurons?

Answer 45

They move materials efficiently across the long distances of axons, ensuring delivery of essential proteins and organelles to the synapse.