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AB1 > CB19: Cell cytoskeleton > Flashcards

CB19: Cell cytoskeleton Flashcards

1
Q

What is the cytoskeleton ?

A

A network of protein filaments that extend throughout the cytoplasm to support its large volume and give the cell its shape.

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2
Q

What do GTP & GDP stand for ?

A

GTP: Guanosine triphosphate
GDP: guanosine diphosphate

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3
Q

What filaments/tubules help to maintain cell shape?

A

Intermediate filaments

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4
Q

What filaments/tubules help the cell to interact with its environment?

A

Intermediate filaments & microtubules

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5
Q

What filaments/tubules are used for movement?

A

Microtubules & actin.

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6
Q

How stable are actin filaments, intermediate filaments & microtubules?

A

Actin filaments: unstable
Intermediate filaments: stable
Microtubules: unstable

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7
Q

What is the diameter of actin filaments, intermediate filaments & microtubules?

A

Actin filaments: small
Intermediate filaments: moderate
Microtubules: large

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8
Q

What are actin filaments, intermediate filaments & microtubules composed of?

A

Actin filaments: identical globular actin molecules
Intermediate filaments: keratin, vimentin, neurofilaments & nuclear lamina
Microtubules: tubulin

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9
Q

What is the structure of actin?

A

A thin double-stranded polymer made of identical globular actin molecules, with + & - ends.

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10
Q

What is the structure of intermediate filaments?

A

Long & rope-like

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11
Q

What is the structure of microtubules?

A

A MT is a long, straight & hollow cylinders composed of 13 protofilaments. Each protofilament is composed of tubulin heterodimers stacked on each other by non-covalent bonds.

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12
Q

How are actin filaments polymerised & depolymerised?

A

Polymerisation by the addition of actin monomers bound to ATP at either end (faster at + end).
Depolymerisation occurs when ATP is hydrolysed to ADP as the structure becomes more loosely packed & disassembly is promoted.

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13
Q

What molecule inhibits polymerisation of actin filaments?

A

Cytochalasins

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14
Q

How is the stability of actin increased?

A

Using phalloidin.

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15
Q

How are intermediate filaments polymerised & depolymerised?

A

Polymerisation:
- 2 alpha-helix monomers bind to form a coiled-coil dimer.
- 2 coiled-coil dimers bind to form 1 staggered tetramer.
- 2 staggered tetramers get tied together & 8 staggered tetramer form 1 IF.
Depolymerisation doesn’t really occur.

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16
Q

How are microtubules polymerised & depolymerised?

A

Polymerisation is by the addition of tubulin bound to GTP to + end of MT. MT grow from a centrosome.
Depolymerisation occurs if GTP is hydrolysed to GDP as the structure becomes more loosely bound.

17
Q

What is the role of the centrosome?

A

It controls the number, location & orientation of growing MT.

18
Q

What is the gamma tubulin?

A

It’s the nucleation site, where the new MT grows from.

19
Q

What are the characteristics of actin filaments?

A
  • Flexible to form small contractile bundles in cytoplasm & contractile rings during cytokinesis.
  • Rigid & stiff to form permanent structures (microvilli).
  • Can be associated with motor proteins (myosin filaments) to take part in muscular contraction.
20
Q

What are the characteristics of intermediate filaments?

A
  • Strong & rope-like to provide high tensile strength which helps the cell to maintain its shape by withstanding mechanical stresses.
  • Forms a network throughout the cell & anchors to plasma membrane at desmosomes to prevent cell rupture.
  • Form cross-links with accessory proteins to interact with other structures.
21
Q

What are the characteristics of microtubules?

A
  • Rigid + can (dis)assembled rapidly to create a system of tracks that can move vesicles & organelles around cell rapidly.
  • Serves as a guide for intracellular transport + an anchor for membrane-bound organelles.
22
Q

How is actin used for movement?

A
  • used in muscle contractions & contractile bundles.
  • Actin is associated with myosin.
  • Actin & myosin contract, which shortens the sarcomere.
23
Q

What are the two types of myosin and where are they found?

A
  • Myosin I is found in all cells.
  • Myosin II is found in muscle cells.
24
Q

How does myosin move?

A

The myosin head hydrolyses ATP & moves towards the + end in a cycle of binding, detaching & rebinding.

25
Q

How are microtubules used for intracellular transport?

A

They use motor proteins kinesin & dynein. Hydrolysis of ATP provides energy for the motor proteins to move.

26
Q

In what direction does dynein move?

A

Towards the - end of the MT

27
Q

In what direction does kinesin move?

A

Towards the + end of the MT

28
Q

What is the structure of kinesin & dynein?

A

They are dimers with a globular ATP binding head. The tail binds to the molecules they are carrying.

29
Q

What is the role of microtubules in cillia & flagella?

A

Cillia & flagella have MT. Dynein moves the MT.

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