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BISC 428 > Lecture 16 > Flashcards

Lecture 16 Flashcards

1
Q

What are the different ways for cells to move?

A

1) Actin-based movements (Lamelipodia, filopodia)
2) Cilia and Flagella

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2
Q

What uses flagella and cilia for motility?

A

Spermatozoa/paramecia

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3
Q

What is the similarity and difference between spermatozoa and paramecia?

A

They are different words
They look like different structures
One is longer
One is shorter
…but they are very similar molecularly
Their main difference is in the way that they beat.

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4
Q

What kind of arrangement are microtubules in?

A

The microtubules are arranged in a 9+2 doublet arrangement

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5
Q

How many protofilaments are in the A and B-tubule?

A

13 protofilaments in the A-tubule, 10 in the B-tubule

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6
Q

How many proteins reinforce the 9+2 microtubules?

A

More than 200 proteins reinforce the 9+2 microtubules

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7
Q

Where are the + and - ends of microtubules located?

A

+ ends of microtubules are at the tip of the flagellum, - ends are towards the head of the sperm

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8
Q

What is flagellar dynein attached to?

A

Flagellar (or axonemal) dynein attached to only the A-tubule of the microtubule doublets

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9
Q

How many repeats of dynein are there?

A

There are 7 diffeent dyneins in the axoneme repeated every 96 nm on the A-tubule

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10
Q

What does altering of dynein do?

A

Altering even 1 of the dynein types can alter the beating

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11
Q

What happens when ATP is added to dynein?

A

With the addition of ATP the dynein engages with the neighbouring microtubule doublet and slides

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12
Q

What does the addition of ATP do to the flagellum?

A

This bends the flagellum

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13
Q

What would happen if there were no doublet microtubules?

A

Without the doublet microtubules, the microtubules would just slide across each other without anything to anchor them

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14
Q

What is also needed?

A

Also needed are links between the B-tubule and the membrane

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15
Q

What is intraflagellar transport?

A

Material needs to be moved to the end of the flagellum/cilium for growth (it grows from the tip)

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16
Q

What does Kinesin-2 do?

A

Kinesin-2 brings material (using “intraflagellar trains”) to the tip using the B- tubules

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17
Q

What does IFT dynein do?

A

IFT dynein (similar to cytoplasmic dynein) brings materials

18
Q

What are intraflagellar trains?

A

Supramolecular protein arrays
They are the primary cargo being transported within flagella
But, they can also be used as adaptors for other proteins to hitch a ride

19
Q

Where do the trains start?

A

Trains start at the basal body and moves towards the tip

20
Q

What happens at the tip?

A

At the tip many cargoes are released, the trains are reorganized and are returned to the cell body

21
Q

Are train cargo interactions strong or weak?

A

Train cargo interactions are thought to be weak
(have never been isolated)

22
Q

How is flagella used in spermatozoa and bacteria?

A

Spermatozoa and bacteria both use flagella for propulsion
Although they look morphologically similar, they are molecularly very different

23
Q

What is the structure of a filament in bacterial flagellum?

A

Rigid helical filaments made from the protein flagellin

24
Q

What is the assembly of flagellum?

A

Flagellin monomers self-associate
Flagellum grows from the tip downwards
Flagellin is secreted through the basal body

25
Q

What is the mechanism of movement for flagellum?

A

Flagellum acts analogously to a boat propeller
ATP is NOT required
H+ gradient across the plasma membrane

26
Q

How fast can flagellum rotate?

A

300-1000 rotations/sec

27
Q

In order for a cell to move, what are 3 key steps to remember?

A

1) Extend a lamellipodium
2) Bind to the surface at the leading edge of the movement
3) Release from the training end of the cell

28
Q

What forms as the cell moves and trailing ones release?

A

New (artificial) junction called focal adhesion (AKA. focal contacts) form as the cell moves and trailing ones release

29
Q

What is coordination likely due to?

A

Coordination is likely due to tension in the cell forcing the release

30
Q

What are focal adhesions?

A

Formed by over 50 proteins
Most are actin-associated proteins

31
Q

What are intermediate filaments at focal adhesions?

A

In non-epithelial cells (eg. fibroblasts; these are more like mesenchymal cells) focal adhesions can bind to vimentin and desmin-based intermediate filaments

32
Q

What can vimentin directly bind to?

A

Vimentin can directly bind to the cytoplasmic region of BI integrin
But, vimentin intermediate filaments can also associate with focal adhesions through plectin

33
Q

What do Kertain 5 and 14 intermediate filaments bind to?

A

Keratin 5 and 14 intermediate filaments can bind to focal adhesions in epithelial cells through plectin

34
Q

What can focal adhesions act as?

A

Focal adhesions can act as nucleation sites for keratin intermediate filaments (hasn’t been shown yet for the other intermediate filament proteins)

35
Q

What happens in plectin KO cells?

A

Intermediate filaments extend beyond the focal adhesion
There are less focal adhesions
(Vimentin KO cells also have fewer focal adhesions)

36
Q

How do intermediate filament associations with focal adhesions increase?

A

Intermediate filament associations with focal adhesions increase when endothelial cells undergo shear stresses

37
Q

Everything about focal adhesions is discussed in the context of?

A

2D cultures

38
Q

What are focal adhesions there for?

A

Focal adhesions are there to fight against Brownian motion. Without focal adhesions the cells would never be able to grasp the substratum.

39
Q

What about in 3D cultures (or when cells are confined)?

A

You don’t have to worry about grasping the substratum because its all around the cell
In 3D cultures (like what you would have in vivo) integrin-based adhesion for directed cell movement is not needed
It’s called “adhesion independent migration”

40
Q

What happens if you block or knock-out integrins?

A

There is no effect on cell motility in 3D!

41
Q

So what do they use to produce force in 3D?

A

Little is known, but potentially cadherins or other molecules.
Or are cells “swimming” in 3D?
Generating constant propelling forces (think of a corkscrew, flagellum or direction motion)

42
Q

So, are focal adhesions real?

A

They have never been seen in vivo

BISC 428 (23 decks)

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