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FBS1 > Cell mobility and cytoskeleton > Flashcards

Cell mobility and cytoskeleton Flashcards

1
Q

What does the cytoskeleton do?

A

Movement of substances around cell, controls cell shape

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2
Q

What are the constituents of the cytoskeleton?

A

Actin microfilaments
Intermediate filaments
Microtubules

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3
Q

Describe actin

A

F-actin is a polymer of g-actin.
Helical polymer 13 subunits/turn
polarised (+/- end)

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4
Q

How does actin grow

A

Actin monomers can be added or removed from either end of the molecule, but is added more quickly at the plus end.
Addition of a monomer requires ATP.

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5
Q

What are the functions of actin?

A

Mechanical support
Changes cell shape
Cell motility

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6
Q

What are the types of actin binding filaments and give examples

A 
Capping
Severing (severin, gelsolin)
Cross-linking - transgelin
Side-binding
Motor
Bundling (a-actinin)
Sequestering (profilin, thymosin)
Membrane attachment (spectrin)
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7
Q

Intermediate filaments

A

Polymer of individual intermediate filament proteins - used to anchor cells at some junctions to other cells or to a basal membrane

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8
Q

Describe the formation of an intermediate filament polymer

A

2 helical dimers form a tetramer; which link in a staggered formation end to end

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9
Q

What does plectin do

A

Links IFs to actin and microtubules

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10
Q

Describe microtubules

A

Rigid, roughly 25nm in diameter.
Made of tubulin alpha and beta monomers in a spiral with 13 columns
Plus end at B side, minus at a

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11
Q

How do microtubules grow

A

GTP hydrolysed to GDP in addition of tubulin

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12
Q

Where are microtubules made

A

Centrosome, minus end of microtubule remains close to the centrosome while the plus end extends into periphery

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13
Q

What is the function of the cytoskeleton?

A 
Cell shape + orientation
Anchoring organelles
Anchoring cells
Cell motility
Movement of intracellular contents and organelles
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14
Q

How does the cytoskeleton aid cell shape and orientation?

A

Actin filament bundles provide support such as in microvilli; but microvilli sheets can maintain the shape of a cell (like in erythrocytes)
Stereocilia in the ear are depolarised/hyperpolarised by deflections caused by sound - actin keeps them rigid.
Intermediate filaments help maintain the shape of axons.
Microtubules stabilise the shape of platelets and axons

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15
Q

How does the cytoskeleton help anchor organelles?

A

Actin hold synaptic vesicles close to the presynaptic membrane; microtubules organise the ER; intermediate filaments form a meshwork around the nucleus of a cell to hold it in position.

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16
Q

How does the cytoskeleton help anchor cells

A

Cytoskeleton anchors the cells to each other or to a basal membrane via junctions

17
Q

How does the cytoskeleton aid cell motility

A

Protrusions pushed out by the cell - actin filament polymerisation provides the force
Protrusions adhere to the surface of the ECM via focal contact junctions
F-actin connects to focal adhesions to provide contractile force
Then the rest of the cell pulls against anchorage proteins to drag itself along

18
Q

What are lamellipodea

A

Exploratory and motile protrusions in the cell surface membrane, produced by the polymerisation of the + end of actin filaments.
They sample the environment, extend and withdraw.

19
Q

How do lamellipodia attach to the surface of the ECM?

A

Via formation of focal adhesions, which are integrins

20
Q

How do lamellipodia contribute to cell mobility

A

Protrusions attach to the ECM via focal adhesions (integrins) then myosin II pulls against it.

21
Q

How does myosin II help with cell motility

A

It pulls against the actin filaments in lamellipodia.
The head region of the actin filaments interact with actin and bind ATP
ATP is hydrolyses so the tail of the myosin moves.
ADP released from myosin head, replaced by ATP.
Myosin head detaches from actin and binds again further along the filament.

22
Q

Where and how do microtubules help with movement?

A

In cilia and flagellae, in respiratory epithelium.
Movt initiated by dyenein (microtubule associated protein) a minus end directed motor protein.
Microtubules bend over as dynein proteins move relative to each other causing microtubules to bend.

23
Q

How does the cytoskeleton help with movement of organelles?

A

Microtubules can act as a railway to help guide the movt of organelles.
Kinesin and Myosin II are the motor proteins involved.
Kinesin is a processive motor protein which ‘walks’ along the microtubule towards the + end of the microtubule.
Dynein moves towards - end
Myosin II jumps short distances, detaches completely from microtubule.

24
Q

What is dynein?

A

A minus end directed motor microtubules associated protein.

25
Q

What are some chemotherapeutic agents that interact with the cytoskeleton in the treatment of cancers?

A

Colchine + vinblastin destabilise the microtubules
Taxol stabilises microtubules
Both inhibit function of mitotic spindle so cell cannot divide.

26
Q

What is Duchenne muscular dystrophy?

A

Mutation in dystrophin, a protein that links actin component of sarcomere to sarcolemma, stabilising it like a shock absorber.
Over time contractile tissue is replaced with fibrous tissue.

27
Q

What is Usher’s syndrome

A

Hereditary blindness, deafness due to myosin VII mutation

28
Q

What is Epidermolysis bullosa simplex

A

Mutation in keratin gene means proper keratin filaments do not form in the skin, blistering in adults and sloughing of skin in newborns. Also caused by plectin mutations but will also have muscular dystrophy

29
Q

What is EB/EBS

A

Epidermolysis bullosa (simplex)

30
Q

What is ALS and what causes it?

A

Amyotrophic lateral scelerosis

31
Q

How can the cytoskeleton contribute to Alzheimer’s disease

A

Microtubule associated protein Tau hyperphosphorylated in tangles and so cannot bind to MT’s

32
Q

What is hereditary spastic paraplegia

A

Mutation in spastin, a microtubule severing protein.

33
Q

What is the diameter od microtubule

A

25nm

34
Q

How many coloumns make up a microfilament

A

13

35
Q

Describe the process of building a microfilament

A

GTP bound monomer bind to + end and are hydrolysed to being GDP bound

vise versa for deconstruction

36
Q

Describe kinesin

A

moves vesicles towards periphery

37
Q

Describe dyenin

A

moves vesicles towards nucleus

FBS1 (74 decks)

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