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BB10005 > Cytoskeleton > Flashcards

Cytoskeleton Flashcards

1
Q

what is the cytoskeleton

A

network of protein filaments throughout cytoplasm, supports large volume of cytosol, dynamic and responsible for cell shape and movement

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2
Q

functions

A 
mitosis
cytokinesis
traffick
support
sperm to swim
muscle contarction
formation of axons/dendrites
cell shape
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3
Q

cortical actin

A

actin filaments found concentrated close to plasma membrane

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4
Q

three types of cytoskeletal filament

A

intermediate filaments
microtubules
actin filaments

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5
Q

intermediate filaments

A

10nm diameter
provide tensile strength
abundant in cells subject to mechanical stress
form a network throughout the cytoplasm, surround nucleus
anchored at plasma membrane at cell junctions
eg keratins

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6
Q

3 main classes of intermediate filaments

A

keratin filaments in epithelial cells
vimentin in connective tissue cells, muscle cells and supporting cells of the nervous tissue (neuroglial)
neurofilaments in nerve cells

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7
Q

construction of intermediate filament

A

from smaller protein subunits
Monomers conisist of globular N (amine) and C (carboxyl) termini, and central rod domain- long alpha helical region in between
two monomers of intermediate filament associate to form a dimer by coiling their alpha helices around each other- coiled-coil conformation
Very strong interaction between monomers because large area in contact with each other
N is start and C end of PP chain

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8
Q

what do two dimers align to form

A

staggered tetramer, N termini antiparallel

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9
Q

what happens to tetramers

A

pack together end to end, N-termini of monomers in one dimer interact with C termini of adjacent monomers in another dimer

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10
Q

next step

A

eight tetramers twisted into rope of diameter approx 10 nm

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11
Q

keratins

A

span interior of epithelial cells

indirectly connected to filaments of other cells through cell-cell junctions (desosomes)

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12
Q

desmosomes

A

cadherins directly make contact with cadherins from another cell
transmembrane proteins that span bilayer and interact with plaque proteins on cytosolic side of membranes
The plaque proteins interact with keratin
keratin-plaque-cadherin-cadherin-plaque-keratin
hence keratin cytoskeletons indirectly connected

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13
Q

epidermolysis bullosa simplex

A

intermediate filament disorder

rare genetic disorder, keratin can’t form normal filaments so skin susceptible to mechanical injury

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14
Q

why are cells with defective intermediate filaments more susceptible to mechanical stress

A

intermediate filaments provide strength and prevent cells rupturing, hold them together when sheet of cells stretched

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15
Q

nuclear lamina

A

network of intermediate filaments inside nuclear membrane

give nucleus its shape

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16
Q

how can you show how durable intermediate filaments are

A

treat with high salt or non-ionic detergent

remain intact

17
Q

actin filament diameter

A

7 nm

18
Q

monomers that make up actin

A

more globular
monomers (vs intermediate filament monomers which only have globular ends) associate head to tail
filaments are unstable without associated proteins

19
Q

monomers that form F actin filament

A

G actin

20
Q

Requirements for formation of F actin

A

presence of ATP, Mg and K
concentration of G actin must be sufficient for polymerisation
Below critical conc, actin filaments depolymerize

21
Q

Polymerisation of actin

A

Actin monomers in the cytosol carry ATP
The ATP is hydrolysed to ADP after assembly into filaments
The ADP bound monomer is less stable in the filament
ADP can’t be exchanged for ATP until the monomer disassembles

22
Q

why do actin filaments have polarity

A

actin monomers all have the same orientation in the filament

minus end has an exposed ATP binding cleft and plus end does not, has a dome

23
Q

What proteins bind to actin and modify its properties

A 
monomer binding proteins
nucleating proteins
cross linking proteins
capping proteins
bundling proteins
motor proteins
24
Q

functions of actin

A

mechanical strength anc cell shape
cell crawling
muscle contraction
organelle movement

25
Q

Cortical actin

A

Actin filaments usually concentrated in a layer under the plasma membrane (cortex)
linked into a meshwork by actin binding proteins
Provide mechanical strength and cell shape

26
Q

cell crawling

A

filopodia or lammelipodia extend a region of the plasma membrane
integrins adhere to extracellular matrix (substrate)
cells use internal contractions to pull itself forwards
Cytoskeleton underneath plasma membrane is deforming the membrane
Will grab onto a suitable substrate via integrins

27
Q

filipodia

A

finger/needle like projections of the plasma membrane

28
Q

lammelipodia

A

sheet like projections of the plasma membrane

29
Q

cell crawling further explanation

A

actin polymerisation at front (plus end) of the cell leads to lamellipodium extension
Attachment to extracellular matrix (via integrins) provides an anchor point
contraction of the rear pulls the cell forward

30
Q

Motor proteins

A

Use ATP hydrolysis
Myosin are motor proteins that can move along actin filaments
Myosin can bind to and hydrolyze ATP
This provides energy for their movement along the actin filament from minus end to the plus end

31
Q

movement of myosin along actin filaments

A

Myosin head lacks ATP at beginning of cycle and is locked onto actin
When ATP binds the affinity for actin is reduced, myosin head released
ATP hydrolysed causes head conformational change, more upright
Then Pi leaves, confromational change and head binds to actin. Then ADP leaves and head conformational change, cocked forwards- power stroke

32
Q

What happens at steady state phase of graph

A

rate of assembly of new subunits same as rate of disassembly

reached critical concentration

33
Q

drugs that interfere with actin filament assembly

A

Cytochalasin D binds to plus end of F actin and prevents addition of further G actin
Phalloidin from poisonous mushroom Amonita binds F actin and prevents actin filaments from depolymerising

BB10005 (27 decks)

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