Moving cargo into the cell

Question 1

Give examples of cell movement

Answer 1

Muscle contraction
Cell migration
Cell shape changes
Intracellular transport
Cytokinesis
Wound healing
Differentiation
Immune defence
Transport of organelles and sub cellular components

Question 2

What is responsible for the movement of vesicles and organelles around cells?

Answer 2

Motor proteins

With either actin filaments or microtubules

Question 3

How do molecular motors work?

Answer 3

Enzyme that converts chemical energy into mechanical energy (usually ATP)
Hydrolysis of ATP is coupled to conformational changes in the protein
Conformational changes move the motor protein along its designated track

Question 4

What are the actin based molecular motors?

Answer 4

Myosin superfamily

Question 5

What are the microtubule molecular motors?

Answer 5

Dyneins

Kinesins

Question 6

How many domains does myosin have?

Answer 6

3

Question 7

What are the 3 myosin domains?

Answer 7

Head
Neck
Tail

Question 8

What is the head domain?

Answer 8

Binds to F-actin and ATP

Uses ATP hydrolysis to generate force

Question 9

What is the neck domain?

Answer 9

Acts as a linker and works as a lever to transduce the force generated by head

Question 10

What is the tail domain?

Answer 10

Mediates interactions with cargo molecules or other myosin tail regions

Question 11

What is myosin II?

Answer 11

Myosin found in muscle
Made of 6 polypetides
2 heavy chains (identical)
2 pairs of light chains

Question 12

What is the n-terminal of myosin II?

Answer 12

The globular head

Question 13

What is the c-terminal of myosin II?

Answer 13

The tail

Question 14

What direction does myosin move in?

Answer 14

All myosin except VI moves towards the plus end of the actin filament

Question 15

Describe the stages of the actin-myosin crossbridge cycle

Answer 15

1. Myosin bound tightly to actin. ATP binding site is empty
2. ATP binds to myosin head. Head unbinds from actin
3. Hydrolysis of ATP. Neck domain displaces head by 5nm
4. Release of Pi and myosin head binds to actin
5. Release of Pi triggers the power stroke. ADP is released

Question 16

What are processive and non-processive motors?

Answer 16

Processive motors work in a coordinated manner

Non-processive motors work independently of each other

Question 17

Describe the processive cycle of myosin V

Answer 17

1. Myosin V dwells with both heads attached. Leading head has ADP bound
2. ATP binding to trailing head promotes dissociation from actin filament
3. Hydrolysis of ATP causes conformational change throwing trailing head forward
4. New leading head binds to actin and then Pi is released
5. ADP is released fro trailing head and the cycle repeats

Question 18

How is non-muscle myosin regulated?

Answer 18

Exists in an inactive folded state
Phosphorylated by MLCK
This causes it to expose actin binding sites
Can spontaneously assemble into filaments
Acts in cytokinesis

Question 19

What are the three parts to kinesin?

Answer 19

Head domain
Neck domain
Tail domain

Question 20

What are the two types of kinesin?

Answer 20

Cytostolic

Spindle

Question 21

What is cytosolic kinesin?

Answer 21

Transports membrane bound vesicle and organelles along well defined routes in the cytosol

Question 22

What is spindle kinesin?

Answer 22

Spindle assembly and chromosome segregation during cell division

Question 23

In what direction does kinesin move?

Answer 23

Always towards the positive end of the microtubule

Question 24

Is conventional kinesin processive or non processive?

Answer 24

Processive

Question 25

Describe the action of kinesin

Answer 25

1. ATP bound to lagging head locks it firmly to the microtubule 2. The leading head weekly docks onto the binding site. Lagging head has hydrolysed ATP to ADP 3. Release of Pi from lagging head weakens its binding. Leading head binds to ATP and locks down 4. Locking down of leading head throws the trailing head forward

Question 26

How is kinesin regulated?

Answer 26

Folding of the kinesin tail hides the binding region | Cargo binding to the tail releases the inhibition

Question 27

What are the variations of kinesin?

Answer 27

Conventional: motor domain at N terminus Motor domain in the middle of the protien Motor domain at C terminus Motor domains at both ends

Question 28

What are the two classes of dyneins?

Answer 28

Cytosolic: move vesicles and chromosomes Axonemal: beating of cilia and flagella

Question 29

What direction do dyneins move in?

Answer 29

Towards the negative end of the microtubule

Question 30

Which is faster, kinesin or dynein?

Answer 30

Dynein is 7x faster

Question 31

Describe cytosolic dynein

Answer 31

Very large protein complex Two almost identical heavy chains forming the head domains Attached to the heavy chains is a stalk and several intermediate chains Cargos are attached via a complex of accessory proteins

Question 32

Describe how cytosolic dyneins move

Answer 32

1. ATP bound state, dynein stalk is not attached to the microtubule. Hydrolysis causes binding 2. Release of ADP and Pi causes a power stroke 3. Power stroke causes a step of 8nm

Question 33

Are dyneins processive or non processive?

Answer 33

Processive