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CMB 1 > cytoskeleton > Flashcards

cytoskeleton Flashcards

1
Q

Which three polymers make up the cytoskeleton

A

microtubules, intermediate filaments, actin filaments

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2
Q

general functions of microtubules

A

organelle positioning,

intracellular transport

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3
Q

general functions of intermediate filaments

A

mechanical strength

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4
Q

general functions of actin filaments

A

cell shape
organelle shape
cell migration

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5
Q

What do accessory proteins regulate?

A
  1. size and rate of filament formation (nucleation)
  2. polymerization/depolymerization
  3. function
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6
Q

Describe the structure of microfilaments

A

helical polymers made of actin, flexible, organsied into 2D networks and 3D gels

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7
Q

describe the structure of IF’s

A

heterogeneous group of filamentous proteins, rope like structure

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8
Q

describe the structure of microtubules

A

hollow tubes made of tubulin

rigid, long, straight

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9
Q

what monomer makes up actin filaments

A

g actin

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10
Q

how does g actin polymerize

A

twisted chain - structural polarity

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11
Q

how thick are actin filaments

A

7nm

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12
Q

What proteins are actin filaments associated with

A

actin binding proteins

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13
Q

what are the three isoforms of g actin

A

alpha - muscle cells

beta and gamma - non muscle cells

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14
Q

how do actin filaments (f-actin) grow

A

addition of g actin at either end

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15
Q

what two factors determine the length of an actin filament

A

concentration of g actin, presence of actin binding proteins (ABPs)

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16
Q

Which 2 ABPs mainly control G actin levels

A

PROFILIN - facilitates polymerization

THYMOSIN B4 - prevents addition of G actin to F actin

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17
Q

What do actin bundling proteins do

A

keep f actin in parallel bundles eg microvilli in epithelial cells

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18
Q

what do cross linking proteins do

A

maintain f actin in a gel like mesh eg cell cortex beneath plasma membrane

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19
Q

what do f actin severing proteins do

A

break f actin into smaller filaments

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20
Q

what do motor proteins do (myosin)

A

transport of vesicles/organelles through actin filaments

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21
Q

function of actin filaments in skeletal muscle

A

arranged in para-crystalline array integrated with different ABPs.
interaction with myosin motors allow muscle contraction

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22
Q

function of actin filaments in non muscle cells

A

cell cortex - forms thin sheath around plasma membrane

associated with myosin forms a purse string ring resulting in cleavage of mitotic cells

23
Q

how do actin filaments aid in cell migration

A
  1. cell pushes out lamellipodia and filopodia at its front - actin polymerization
  2. protrusions adhere to surface - INTEGRINS link actin filaments to ECM surrounding cell
  3. cell contraction and retraction at rear - interaction between myosin and actin filaments
24
Q

what makes IFs tough

A

resistant to detergents, high salt etc.

25
Q

width of IFs

A

8-12nm

26
Q

nuclear function of IFs

A

strengthen nuclear envelope

27
Q

how do IFs form a network

A

join up to desmosomes throughout cytoplasm - withstands mechanical strength when stressed

28
Q

what are the three parts of an IF unit

A

N terminal globular head
C terminal globular tail
central elongated rod like domain

29
Q

what do to IF units form

A

a dimer

30
Q

what do every 2 IF dimers form

A

tetramere

31
Q

how do IF tetrameres form a filament

A

bind to each other and twist to constitute rope like filament

32
Q

what types of IF are found in the cytoplasm

A

KERATIN - in epithelia
VIMENTIN (related) - connective tissue, muscle cells, neuroglial cells
NEUROFILAMENTS - in nerve cells

33
Q

what are the nuclear IFs

A

nuclear lamins - in all nucleated cells

34
Q

what do Intermediate Filament Binding Proteins do

A

linkers of IF structures/stabilize and reinforce IF into 3D networks

35
Q

what is fillagrin

A

an IFBP than binds keratin filaments into bundles

36
Q

what are synamin and plectin

A

IFBPs that bind desmin and vimentin, link IF to other cytoskeleton compounds eg actin/desmosomes

37
Q

what are Plakins

A

IFBPs that keep contact between desmosomes of epithelial cells

38
Q

functions of IFs in the cytoplasm

A

provide tensile strength

structural support - create deformable 3D network, reinforce cell shape and fix organelle localization

39
Q

functions of IFs in nucleus

A

form mesh, line inner face of NE to strengthen and provide attachment sites for chromatin

40
Q

role of IFs in cell division

A

dissemble and reform at each cell division as nuclear envelope disintegrates

41
Q

structure of microtubules

A

hollow tubes made of tublin, relatively stiff 25nm, polarized

42
Q

microtubules are dynamic - what does this mean

A

assesmble and disassemble in response to cell needs

43
Q

how is tubulin distributed in the cell

A

roughly 50:50 free or in filament

44
Q

how do microtubules polymerize

A

starts at Microtubule Organizing Centre (MTOC) - αandβ heterodimers - growth is polarized; faster at +ve end

45
Q

where is the MTOC in most cells

A

centrosome - contains gamma tubulin ring that initiates microtubule growth

46
Q

function of microtubules in intracellular transport

A

act like railway tracks for molecular motors - different motors for different cargoes - directionality is vital

47
Q

function of microtubules in organelle positioning

A

organizes their position - providing polarisation of cells - directionality is vital

48
Q

how do microtubules contribute to rhythmic beating of cilia and flagella

A

motile processes w/ highly organized microtubule core

49
Q

what is an axoneme

A

core of cilia and flagella

50
Q

what constitutes an axoneme

A

9 pairs of microtubules around 2 central axonemes

51
Q

what is bending of cilia and flagella driven by q

A

motor protein dynein

52
Q

whats the basal body

A

at base of tubule, controls axoneme assembly

53
Q

big microtubule examples

A

cilia - resp tract - sweeps mucus and debris from lungs

flagella on spermatozoa

CMB 1 (3 decks)

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