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MCB - Cell Bio > Cytoskeleton (+ intro) > Flashcards

Cytoskeleton (+ intro) Flashcards

1
Q

why does compartmentation exist?

A

structural organisation and set up distinct biochemical environments for specific reaction

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2
Q

genome size

A

bacteria/archaea - size related to number of protein coding genes

eukaryotes - genes and genome size not linear relationship (humans much bigger genome but same no. genes as worm) because of multicellular complexity

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3
Q

how do cells cope with multicellularity?

A

cell cycle: 4 phases
gap phase prepares for replication and monitores env.
S phase where genome copied
M phase (prophase, prometaphase, metaphase, anaphase, telophase, cytokinesis, and checkpoints in between)

controlled proliferation and PCD (apoptosis/autophagy)

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4
Q

3 types of cytoskeleton (diagrams on word)

A

microfilaments (actin): 7-9nm diameter

microtubules (alpha-beta dimer): 25nm

intermediate filaments: 10nm

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5
Q

cytoskeleton function

A

makes sure compartments are in the right place,

vesicles transported

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6
Q

cytoskeleton in epithelial cells in gut

A

microvili made from actin
microtubules
interfilaments link desmosomes and hemidesmosomes for structural rigidity

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7
Q

microtubule structure (diagram on word)

A

barrel with lumen forms tube
13 protofilaments round in circle and link together to form barrel
protofilaments are repetitive alphabetaalphabeta tubulin
a-b dimer (homologues of each other) bind existing microtubule

solid, rigid, hard to snap under pressure

2 diff ends: beta +ve end, alpha -ve end
so motor proteins go in 1 direction

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8
Q

2 ends of microtubule

A

+ve beta end

-ve alpha end

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9
Q 
microtubule growth (Cc, GTP)
(diagram on word)
A

alpha-beta tubulin dimers only form polymer when above critical concentration (Cc)
Cc threshold lower at + end (than -ve) so grow at + end
can also grow at ‘-‘ when high enough conc. but preferential ‘+’ growth

increased conc. means increased tubule mass so longer

reducing below Cc means disassemble also at + end

a&b both bind GTP, hydrolysed to GDP on beta to form main body of tubule
+ has faster polymerisation than hydrolysis so GTP not turned to GDP so makes GTP cap at + end
hydrolysis faster at - end so always GDP form

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10
Q

treadmilling (microtubules)

A

rate of addition at + end = rate of disassembly at - end

so stays same length

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11
Q

taxol drug (microtubules)

A

binds beta and prevents depolymerisation of microtubule

treatment for ovarian/breast cancer by preventing mitosis

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12
Q

colchicine and colcemid drug (microtubules)

A 
binds alphabeta dimer
prevent addition (polymerisation) to microtubule
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13
Q

MTOC (microtubules)

A

microtubule organising centres - point from which they emerge
conc around nucleus
originate from single point
grow from centrosome

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14
Q

dynamic instability (microtubules)

A

get to point when stop growing then depolymerise and collapse to spot (MTOC)

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15
Q

centrosome (microtubules)

A

2 centrioles in centrosome matrix make a centrosome
close to plasma membrane
duplicated every cell cycle
microtubules grow from gamma-tubulin ring complexes (nucleating sites) - bind minus end (a) so prevent addition
accessory protein in gamma is bridge between microtubule and centrosome

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16
Q

shrinking and dynamic instability (microtubules)

A

growing filaments are straight
shrinking are curved/frayed

hydrolysis to GDP when touch membrane so peel off and back to dimers
conformational change in beta changes angle of dimer so cap lost and fall apart from loss ability to stick

dimers turn to GTP form again so can add

catastrophe then rescue

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17
Q

3 functions of microtubules in mitosis

A 
separate chromatids (+ attaches to centromere)
interpolar microtubules in the middle, 2 sitting on top of each other and forces apart

astral microtubule connect to plasma membrane, to centre the spindle in cell so 2 cells are same size

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18
Q

MAPs (microtubules)

A

microtubule associated proteins regulate MT stability and function

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19
Q

+ end MT binding proteins (microtubules)

A 
EB-1
DASH ring complex
cross-linking, stabilising, bundling proteins (bind site of MT)
MAP2
Tau
MAP65 (Ase1)
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20
Q

EB-1 (microtubules)

A

end binding protein 1

only binds GTP tubulin on growing MTs so stabilise cap and MT seam (in between filaments, seam closes barrel into tube)

other protein complexes can bind so move to plasma membrane as grows

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21
Q

Dam1/DASH complex (microtubules)

A

fungal specific heterodecamer
bind polymerising/depolymerising MTs and couples kinetochore movement to MT depolymerisation

proteins bind in ring around tubule - inside of ring -ve and outside of MT -ve so repel each other, don’t touch but glide along protofilaments
splaying MT prevent ring falling off in depolarisation (like fraying to the sides)

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22
Q

MAP65 (microtubules)

A

bind sides and stabilise anti-parallel MTs

important for bi-polar spindle formation in middle where from diff side on top of each other

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23
Q

MAP2 & Tau (microtubules)

A

binds sides and stabilise parallel MTs to keep apart and protect (stabilise axon for vesicles transport of NT)
promote polymerisation and inhibit catastrophe

+ve tail binds -ve MT surface

MAP2 tail bigger than Tau tail so gap between MTs bigger when use MAP2

MAP2: dendrites, between MTs and interfilaments
Tau: dendrites/axon, bridge between parallel MTs

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24
Q

Alzheimer’s and microtubules

A

Tau MT binding protein mutated so can’t transmit vesicles for synapse so defect in brain

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25
motor proteins
use ATP to walk, mostly to +ve end, cargo can be another MT to slide against Kinesin: stabilise, de-stabilise, bundle MTs, +ve end directed (some -) Dynein: fast -ve end directed can have both types for movement in both directions
26
structure of kinesin (diff types)
head, stalk, tail ``` kinesin-1 = conventional, homodimer 2 same subunits kinesin-2 = heterodimeric kinesin-5 = bipolar, 2 heads both attach to MT kinesin-13 = speed disassembly ```
27
kinesin movement
head binds ATP/ADP for walking 1) motor head has catalytic core (in 2 motor heads) and neck linker (linking 2 catalytic cores) binds to MT (1 head always bound) and ADP released so ATP enters binding site 2) conformational change so neck linker zips onto catalytic core of 1st head so throws 2nd head forward to next binding site on MT because loses bond on MT 3) behind head now ATP to ADP
28
dynein structure (see diagram lecture 18 page 2)
2 stalks sit on MT with dynactin (co-factor for dynein) 2 heavy, 2 inter, 2 light chains so double headed and 2 binding domains but requires dynactin dynactin binds heavy chain stem connected to head domain where ATPase is 6 ATPase domains arranged in wheel including major ATPase Arp1 (actin related protein) polymer, link dynein to cargo domain
29
dynein transport
major ATPase causes conformational change so changes tail position relative to wheel and stalk changes where bound to MT
30
centrioles
make centrosome MTs arrange in circle 2 MT circles share subunits for 2 centrioles (like infinity shape)
31
actin overview
``` double helical twist structure diff types with diff functions binds ATP (not GTP like MTs) formed from large no. diff places so lots in cell highly dynamic grow and shrink at both ends (polarised +ve and -ve end) tracks for myosins motor proteins form static and motile structure ```
32
types of actin structure: static and motile (diagrams on word)
arranged in diff way for diff function microvilli are static cells in monolayer leading edge: crosslinked filaments force plasma membrane forward for migration stress fibres: parallel bundles squeeze cell to push nucleus forward for migration (long lines in middle of cell while leading edge crosslinks on front edge) contractile ring: when dividing in cytokinesis cell cortex: inside edges
33
actin structure (monomers together form filaments)
G-actin (globular monomer) divided by central ATP binding cleft at minus end (in middle of G-actin monomer structure) lots G-actins form strands F-actin (filamentous form) 2 strands, helices twist polarity: ATP binding opposite of adjoining molecules so ATP on minus end
34
how long is actin?
72nm long with symmetry every 36nm (whole 8 shape vs half of 8 shape)
35
how do actin filaments form? (time graph, rate of addition, treadmilling
actin subunits charged with ATP, add salt to join and form oligomers (few subunits together) grow from + and - end so rapid elongation time graph: slow, oligomers then fast then steady state horizontal line when preformed filaments added, there's no lag on graph rate of addition of ATP-G-actin higher at + end and dissociates fast at -ve so bind on + preferentially ATP-actin added at + ADP-actin removed at - because ATP hydrolysed to ADP when binds causing treadmilling
36
CC for actin
critical conc Cc is when stays same length so assembly=disassembly below Cc disassemble above Cc grow
37
actin binding toxins
sit in ATP binding site to stabilise actin
38
actin binding proteins
``` capping severing enzymes bundling cross-linking monomer binding proteins filament nucleators ```
39
capping (actin binding proteins)
keeps inactive till need to create filaments on + and - end to prevent pol/depolymerisation traps at specific size Cap2 bind + end to stop addition and loss Tropomodulin binds - end so promotes growth (stop loss so only growth from +)
40
severing enzymes (actin binding proteins)
degrade filaments to reuse actin Severin, Gelsolin, ADF-Cofilin Cofilin binds side of ADP-actin and fragments the filament so replenish ADP-actin pool (can be recharged by profilin)
41
bundling (actin binding proteins)
form structures Fibrin, alpha-actinin, Villin
42
cross-linking (actin binding proteins)
support for plasma membrane Filamin
43
monomer binding proteins (actin binding proteins)
excess G-actin monomer so need to restrain it, nucleation to filaments (growth) Profilin/Thymosin beta work against each other ``` G-actin ADP or ATP form bound to thymosin b4 so can't add it to filaments. profilin competes (binds more weakly than thymosin) for G-actin and causes ATP to remove ADP so puts in active state ready to be put on existing filament ```
44
filament nucleators
aid polymerisation at right place of straight or branched filaments Formin, Spire, Arp2/3 complex extracellular signals through G protein tells cell to make actin at specific point: 1) Rho GTP activated and binds RBD (Rho binding domain in Formin) so unfolds Formin 2) FH1 in Formin recruits ATP bound actin to profilin and act as docking site to add more actin on + end 3) FH2 holds actin filament as it grows and pushes plasma membrane forward branch networks 70 degree angle between existing filament and branch coming off side Arp2/3 complex activated by WASp - at leading edge so signal to make branch exterior signal received by plasma membrane and activates Cdc42 GTPase so WASp recruited to membrane and conformational change releases Arp2/3 binding domain so recruits monomers and branch polymerisation
45
WASp
multi-domain RBD (Rho GTPase binding domain) actin binding domain Arp2/3 binding domain
46
actin-related proteins
Arps dynactin complex, Arp2/3
47
actin in pathogens
viruses and bacteria use actin machinery to move themselves around Arp2/3 stimulated by proteins on bacteria - Cofilin disassembles so reuse actin at front so move Act A protein stimulates actin and mimics action of WASp
48
organisation of actin
microvilli - tightly packed stress fibres - loosely packed, space for motor proteins filamin - crosslink between 2 filaments but not connected, mesh underlies plasma membrane dystrophin - skeletal muscle protein links actin to plasma membrane via glycoprotein
49
what is myosin?
motor proteins on actin filaments (unlike kinesins and dyenins on MTs and no motor proteins on interfilaments)
50
3 myosin types (only these in yeast so others are specific to humans)
I: only 1 head (other 2 have 2), cargo is static piece of membrane, myosin/membrane don't move, only actin moves II: cargo is themselves, anti-parallel overlapped, bouquet structure, actin move relevant to head of myosin, muscle contraction. short legs V: walks along track, 2 heads and adaptor protein carries object along actin, long legs
51
what do mutations in myosin cause?
deafness and blindness
52
myosin II structure (diagram on word)
bi-symmetrical bouquets = dimers connected by coiled-coil tail region (heavy chain) essential light chain and regulatory light chain ATP binding within head domain linker region - light chains together Chymotrypsin cleaves most of coiled tail region Papain removes remainder of tail (S2 region) leaving S1 heads
53
polarity of actin
seen on electronmicrographs saturate binding of myosin S1 heads arrowhead appearance pointing to minus end - tells which direction actin going in
54
mechanisms of muscle myosin II
1) myosin head bound to actin 2) ATP binds and head released 3) hydrolysis of ATP to ADP+Pi so head moves forward (cocking) 4) with ADP, can bind actin 5) loss of Pi from nucleotide binding site causes power stroke so pushes actin back 6) ATP replaces ADP so head releases and repeat (actin doesn't go back because lots heads bound at same time
55
myosin vs kinesin
structural similarity myosin released from actin when ATP binds but kinesin bound to MT when ATP bound and released when hydrolysed power stroke by loss of Pi vs ATP binding in kinesin
56
skeletal muscles (structure on word)
syncytial (multi-nucleated) made of myofibrils which made of repeating sarcomeres around myofibrils is nuclei, sarcoplasmic reticulum, transverse tubules (T-tubules)
57
sarcomere structure
Z disc, light band (actin), dark band (myosin) stays same length so capped and no polymerisation/depolymerisation, same length in all muscle darkest region is actin myosin overlap myosin in middle have 6 actin filaments to walk along
58
Nebulin mutation in skeletal muscles
length of actin changed
59
Titin
biggest proteins in human body | prevents over-stretching of sarcomere but can rip when pull muscle
60
mechanisms of skeletal muscle contraction
upon neuronal stimulation, calcium travels down T-tubule to ER and triggers channel to release more Ca Ca binds to troponin which is bound to tropomyosin and causes conformational change so slide tropomyosin away from binding site and myosin can bind
61
cardiac muscle
striated not syncytial - lots nuclei in 1 cell so not divided gap junctions so AP spread quickly mutations in actin/myosin leads to disease
62
actin/myosin role in cytokinesis and link to CyclinB/Cdk1
CyclinB/Cdk1 activation causes mitosis inactivation causes cytokinesis - MLCK (myosin LC kinase) turns myosin on to free state so bundles in bouquet and ring around cell membrane to squeeze to separate membranes in cytokinesis
63
laser based optical tweezers
static actin bound to beads held by optical trap under microscope myosin stuck on another bead move object outside of optical trap - detect in movement, how quick etc.
64
myosin leg size
velocity of movement increases as leg size increases because bigger step size so longer distance covered but same rate of binding myosin I moves 10-14nm step size II moves 5-10nm V moves 36nm
65
how movement of myosin II and myosin V differs
II releases actin and head returns so only 10% time attached | V is processive so takes successive 36nm steps and attached 70% of the time, so 1 head always bound
66
myosin V in budding yeast
transport membrane cargos like vesicles | and can control gene expression
67
examples of motility with cytoskeleton
1) wound healing in zebrafish larvae, lymphocytes move out blood vessels to wound 2) slime mould move to cAMP highest conc 3) macrophage chasing bacteria, sense where from tripeptide signal 4) keratocytes pulling off fish scale, locomotion
68
locomotion
1) EXTENSION - of lamellipodium from leading edge, actin polymerisation moves membrane forward 2) ADHESION - feet established, filopodia, capping of actin filament bundles 3) TRANSLOCATION - actin and myosin contract at back end so force cytoplasm and nucleus forward 4) DE-ADHESION - endocytic recycling, release last adhesion site at back, internalise membrane and integrins, transports to front to use again
69
structure of cell in locomotion
lamellipodia at front end - branched actin nucleated at plasma membrane to push forward (Arp 2/3) filopodium stick out front - parallel tight bundles of actin, by Formin, bundled by Fimbrin stress fibres at back - contractile bundles loosely, myosin works on actin to contract and pul nucleus cell cortex - gel like network, cross-linked actin, not involved in movement
70
chemotaxis movement
Cdc42 GTPase activation promotes Formin for filopodia growth and Arp2/3 actin assembly to promote lamellipodia growth Rac GTPase promotes branched assembly behind leading edge Rho GTPase activation at lagging edge - stress fibre formation, myosin II, cell contents move forward
71
regulation of movement by Rho GTPases
diff dominantly active G protein versions in fibroblast cells produce diff structure if Rho dominantly active then stress fibres made Rac - lamellipodia (membrane ruffles) made but no directional movement without sense Cdc42 - filopodia (membrane actin spikes) plus end comes out edge
72
chemoattractant effect
sensed by receptors on cell at front end activates Cdc42 and Rac so filopodia and lamellipodia form
73
chemorepellent effect
Rho inhibits at front and activates at back so myosin and actin cause stress fibres to form and contract
74
wound effect on cell movement
cells migrate towards each other to fill gap
75
cilia and flagella (diagram on word lecture 21)
highly motile, containing MTs and dyneins both almost identical but flagella longer than cilia flagella helps sperm swim cilia on paramecium basal body sits in cytoplasm and tethers and nucleates axoneme (main body) through transitional zone top of basal body has 9 pairs of triplets (like centriole) axoneme has 9 pairs of doublets and 2 central MTs
76
metachronal wave
beating cilia, moves particles over surface like mucus
77
cilia and flagella mechanisms and movement
dynein motor proteins walk on it cross-linked MTs in axoneme transmit sliding force between tubules, in experiment - ATP added - tubules slide not bend (bend when normally crosslinked by nexin), other crosslinked are arms of dynein when dyneins activated to walk, cause kinks that move to tip of flagella/cilia to cause power stroke and motor protein dynein move from + to - towards basal body
78
intermediate filaments main features
``` 8-10nm diameter don't bind nucleotides tensiles strength like ropes assemble onto pre-existing filaments less dynamic unpolarised no motor proteins structural integrity ```
79
interfilament proteins
same structure classes 1-5 head groups determine class
80
structure of intermediate filament
base unit dimer with N and C-terminal blobs close proximity, wrapped around anti-parallel link head to head - tetramer - bind to other to make protofilament - 4 makes protofibril and twist to intermediate filament
81
classes of intermediate filaments
1 & 2: keratins in epithelial cells for strength and integrity, only in vertebrates, attached to plasma membrane through desmosomes and to extracellular matrix through hemidesmosomes 3: muscle, mechanical scaffold to sarcomere, stop overstretch 4: neurofilaments, support axons, determine diameter so rate of impulses 5: nuclear lamins inside nuclear envelope, nucleus support, link membrane and chromatin, mutation causes progeria and other nuclear lamin diseases
82
skin keratins
diff in diff layers K5 and K14 in basal layer then move up skin and express K1 and K10, and dead in stratum comeum mutations in 5/14 causes blisters and susceptible to rips

MCB - Cell Bio (3 decks)

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