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FBS1 CBS > cytoskeleton > Flashcards

cytoskeleton Flashcards

1
Q

what are the 3 filament types (smallest to largest)

A
  1. actin (microfilaments) - actin-binding proteins
  2. intermediate filaments
  3. microtubules: microtubule-associated proteins (MAPs)
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2
Q

describe actin structure

A
  • F-actin
  • polymers of actin proteins called G-proteins
  • polarised double helix
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3
Q

how many acts subunits for each complete turn? diameter?

A

13

7nm diameter

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4
Q

explain growth of actin filament

A
  • ATP bound to actin monomer (G-actin)
  • monomers added/removed from both ends of polymer
  • add more rapidly to +end
  • once incorporated, ATP –> ADP
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5
Q

3 main functions of actin

A
  1. mechanical support
  2. cell shape changes and maintenance
  3. cell motility
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6
Q

9 functions/roles of actin proteins

A
  1. G-actin monoers
  2. actin-sequestering proteins (eg. profilin, thymosin) prevent G-actin polymerising
  3. actin-bundling proteins (a-actinin in muscle))
  4. motor proteins (muscle myosin)
  5. side-binding proteins (interact w other proteins)
  6. capping proteins (prevent growth)
  7. cross linking proteins (eg. transgelin)
  8. severing (gelsolin, severin)
  9. membrane attachment proteins (spectrin)
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7
Q

diameter intermediate filaments

A

10nm

visible by e.m.

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8
Q

functions of intermediate filaments

A
  • dense around nucleus
  • anchor cells at some cell junctions
  • support nuclear structure
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9
Q

examples of intermediate filaments

A

Named vary by cell types:

eg. keratin, vimentin, glial fibriallary acidic protein, neurofilamin

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10
Q

how is an intermediate filament polymer formed

A
  1. monomer
  2. helical dimer (2 monomers)
  3. 2 dimers combine = tetramer (fundamental unit)
  4. tetramers link - staggered formation
  5. Subunit exchange is slow but occurs throughout the length of the filament.
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11
Q

example of modulation of IF

A

plectin molecules link IFs to actin filaments and microtubules

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12
Q

diameter microtubules

A

25nm

visible by e.m. or light microscopy

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13
Q

describe structure of microtubules

A
  • polymer built from TUBULIN monomer which consist of one molecule of a-tubulin and beta-tubulin
  • asymmetric monomer: polymer has polarity (one end stops with a, one with b)
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14
Q

describe arrangement of columns of tubulin

A

13 columns of tulip polymer arranged in hollow cylinder

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15
Q

assembly and disassembly of microtubule

A
  • (negative) end: GPD bound monomers dissociate rapidly
  • GTP bound monomers assemble onto + end

GTP–>GDP, cycle starts again

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16
Q

where are microtubules polymerised

A

centrosomes

minus end remains close to centrosome, plus end points out towards cell periphery

17
Q

how does cytoskeleton help cell shape and orientation

A
  • actin: support. maintain shape of cell e.g. erythrocytes
  • IF: stabilise axon shape
    microtubules: stabilise shape of platelets and axons
18
Q

how do stereocilia detect vibration in cochlea

A

The cells are depolarised or hyperpolarised by deflections caused by sound.
Actin filaments keep the stereocilia rigid.

19
Q

how does cytoskeleton help anchoring organelles

A
  • actin: hold synaptic vessels close to presynaptic membrane
  • IF: hold cell nucleus
  • microtubules: organise ER of a cell
  • cytoskeleton holds cell next to each other and to extracellular matrix at cell junctions
20
Q

describe 4 steps of actin-based cell movement

A
  1. leading edge - cell push forward. actin polymerises
  2. focal contact junctions allow adherence of projections. F-actin connects focal adhesions
  3. backside of cell pulls against anchorag epounts
  4. actin depolymerises at rear
21
Q

what are lamellipodia and how do they function

A
  • sample environment - extend and withdraw
  • plus end of actin orientated to cell periphery
  • When lamellipodia or filopodia touch down: attach to the extracellular matrix through the formation of focal adhesions (focal contacts)
  • Actin connect the focal adhesion to the rest of the cytoskeleton
22
Q

how does myosin help actin

A

myosin II: motor protein

  1. head region interacts w actin and binds ATP. Energy release from hydrolysis = myosin tail moves
  2. ADP released from head and replaced by ATP = detach from actin
  3. head binds further down filament
23
Q

describe microtubule based movement

A
  • cilia
  • 9+2 structure
  • DYNEIN (a MAP): initiate movement. minus end-directed motor protein
  • microtubules slide along each other = bend cilium
24
Q

how does cytoskeleton help movement of intracellular contents

A

microtubules

e. g. move synaptic vessels along axons to synapse
- motor proteins kinesin (moves to + end) and dynein (moves to - end) move vesicles

25
Q

what’s the difference in the action of kinesis and myosin II

A
  • kinesin stays attached to microtubule during ATP hydrolysis = processive motor protein. moves large distances
  • myosin II: detaches from actin at end of the cycle, travel short distances
26
Q

e..g. when cytoskeleton is used tome cell contents

A

separation of chromosomes during cell division - microtubules

27
Q

3 anti-cancer therapeutics and their mechanism

A

colchicine, vinblastine, taxol

  • inhibit function of mitotic spindle and thus cell division
  • C&V: destabilise microtubules, T stabilises
28
Q

actin abnormalities leading to disease

A
  • mutation in dystrophin = Duchenne and Becker Muscular Dystrophy
  • mutation in myosin VII = Usher’s syndrome - heriditary deafness and blindness
29
Q

intermediate filament abnormalities leading to disease

A
  • Epidermolysis bullosa symplex

- Amyotrophic Lateral Sclerosis (ALS, Lou Gehrig’s Disease)

30
Q

microtubule abnormalities leading to disease

A
  • Alzheimer’s Disease

- Hereditary Spastic Paraplegia

31
Q

how does Listeria bacteria affect actin cytoskeleton

A
  • engulfed by host cell
  • escapes
  • F-actin polymerises at back of bacterium = motility
  • drives bacterium into neighbouring cell
32
Q

what is Epidermolysis bullosa symplex.

A

IF

  • Mutations in keratin genes= failure to form proper keratin filaments in epidermis
  • skin sensitive to mechanical injury
  • Blistering in adults, sloughing of epidermis in newborns
  • Plectin mutations also cause EBS with muscular dystropy
33
Q

Amyotrophic Lateral Sclerosis

A

IF
(ALS, Lou Gehrig’s Disease).
-Some hereditary forms are caused by mutations in neurofilamin genes
-causes of motor neuron degeneration are unclear.

34
Q

Alzheimer’s Disease.

A

microtubules

  • Alongside amyloid plaques, AD brains display neurofibrillary tangles comprising the MAP, Tau.
  • Tau is hyperphosphorylated in tangles and cannot bind MTs.
35
Q

Hereditary Spastic Paraplegia

A

microtubules

The most common form is caused by mutations in spastin, a microtubule severing protein.

FBS1 CBS (7 decks)

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