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Cellular Biology and Biochemistry > Moving cargo into the cell > Flashcards

Moving cargo into the cell Flashcards

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1
Q

Give examples of cell movement

A 
Muscle contraction
Cell migration
Cell shape changes
Intracellular transport
Cytokinesis
Wound healing
Differentiation
Immune defence
Transport of organelles and sub cellular components
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2
Q

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

A

Motor proteins

With either actin filaments or microtubules

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3
Q

How do molecular motors work?

A

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

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4
Q

What are the actin based molecular motors?

A

Myosin superfamily

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5
Q

What are the microtubule molecular motors?

A

Dyneins

Kinesins

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6
Q

How many domains does myosin have?

A

3

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7
Q

What are the 3 myosin domains?

A

Head
Neck
Tail

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8
Q

What is the head domain?

A

Binds to F-actin and ATP

Uses ATP hydrolysis to generate force

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9
Q

What is the neck domain?

A

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

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10
Q

What is the tail domain?

A

Mediates interactions with cargo molecules or other myosin tail regions

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11
Q

What is myosin II?

A

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

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12
Q

What is the n-terminal of myosin II?

A

The globular head

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13
Q

What is the c-terminal of myosin II?

A

The tail

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14
Q

What direction does myosin move in?

A

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

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15
Q

Describe the stages of the actin-myosin crossbridge cycle

A
  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
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16
Q

What are processive and non-processive motors?

A

Processive motors work in a coordinated manner

Non-processive motors work independently of each other

17
Q

Describe the processive cycle of myosin V

A
  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
18
Q

How is non-muscle myosin regulated?

A

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

19
Q

What are the three parts to kinesin?

A

Head domain
Neck domain
Tail domain

20
Q

What are the two types of kinesin?

A

Cytostolic

Spindle

21
Q

What is cytosolic kinesin?

A

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

22
Q

What is spindle kinesin?

A

Spindle assembly and chromosome segregation during cell division

23
Q

In what direction does kinesin move?

A

Always towards the positive end of the microtubule

24
Q

Is conventional kinesin processive or non processive?

A

Processive

25
Q

Describe the action of kinesin

A
  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
26
Q

How is kinesin regulated?

A

Folding of the kinesin tail hides the binding region

Cargo binding to the tail releases the inhibition

27
Q

What are the variations of kinesin?

A

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

28
Q

What are the two classes of dyneins?

A

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

29
Q

What direction do dyneins move in?

A

Towards the negative end of the microtubule

30
Q

Which is faster, kinesin or dynein?

A

Dynein is 7x faster

31
Q

Describe cytosolic dynein

A

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

32
Q

Describe how cytosolic dyneins move

A
  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
33
Q

Are dyneins processive or non processive?

A

Processive

Cellular Biology and Biochemistry (22 decks)

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