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2- 33-Actin filament (20 Oct) microtubial (23 Oct) (6- microtubules…
2- 33-Actin filament (20 Oct)
microtubial (23 Oct)
1- building block= actin monomer
Actin monomer has ATP binding site imp. in polymerising the actin filament
diff. from microt. which has alpha and beta sub units
actin has 1 unit
nucleating takes time
3 monomers make a nucleus of actin filament
as soon as you make a nucleus the polymerisation will happen very quickly
when you reach certain length as a filament
, the number of actin filaments will maintain
rate limiting step is nucleation
2- looking at elecro microcraph
see the arrow shape
the plus end is barbed > and the
minus end is pointed
plus end = usually a growing end
actin monomers come in and make a longer chain
in minus end we loose actin monomers
so we end up in the same length
so actin is dynamically changing
that is called treadmealing
how actin filament maintain the constant length
is by treadmilling
we add new monomers at right but keep loosing actin monomers at the left which is the minus end
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3- accessory proteins are a lot of proteins which
will help to assemble quicker or breack down quicker... making more stabe
formin= ring shape protein
attaches to the end of the plus end
rotates and exposing actin binding site
that will spatially help coming in actin monomer to go to the right place with formin
Formin has wiskers and wiskers bind to the profilin which
will grab the monomers and by changing the conformation of the arm of wiskers they can place the monomer actin into the right binding sight , that will accelerate the actin filament formation
Arp 2/3 prot.
will make 90 degree branching of the actin filament
helpful for crating flat structure
this is the main structure found in laminapodia
when cell has to move they have a wavy structurep
filopodium is the long pointy ones are filopodium
when cells move filopodium reach out
feel about it if they like it they move towards it and they form lamina podia and they move twards thet end
4- different structures
will make 90 degree branching of the actin filament
helpful for crating flat structure
this is the main structure found in lamellipodia
when cell has to move they have a wavy structurep
filopodium is the long pointy ones are filopodium
stress fiber
cells use the same actin filament
but by changing the decoration proteins they can create
different structures
5- Actin filaments usually work together with myosin
Myosin II will give us the muscle force
myocin is around 150 nm with 2 head
they can form larger structure
half of them facing right hand side and half will put the head on the left hand side
arrangemnet of myocin head is spiral structure
myosine can bind to actin filament and as soon as you have ATP >>> and ATP binds to the head of the myocine the myocine head will hydrolyse the ATP into ADP and inorganic phosphate
changes the conformation of the :!?:
will move to the right handside
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actin has a motor protein which is myosine
to create the contractile forces
myosin super family
myosin 5 has a lot longer length if swinging
30 to 40 nanometer swing
6- microtubules
have hetrodimer system
meaning two differet monomers forming a nuclear
alpha tublin in light green and beta tublin
you'll see a lot of linear protofilament
that will form a hollow tupe formation to make microtubial
mictotubial has a lot of different shapes
2 different shapes:
1- centrosome
2- cilia and :!?:
similar to actin filament it has a growing end versus a non growing end
plus end vs minus end
on the plus end it will keep growing
the florescent shows the edges of the growing end
whenever it lights up it is growing
microtubial changes all the time
even though the time scale is slow
how to control the dynamic movements od microtubule
one method is putting a GDP cap , different from Actin filament , actin filament uses ATP
the tubule uses GTP as an energy source
as soon as we see GTP cap on the growing plus end it will keep grow
you will see a lot coming out of centrosome which is a growing centre
as soon as you loose the GTP cap because GTP hydrolyses to GDP and inorganoc phosphate
that signal triggers loosing a lot so on the plus end you can grow as well as shrink
because microtubule always have a centre of growth which is centrosome so they always come out of the centrosome or retract towards the centrosome
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centrosome has pore structures which is gama tublin ring complexes :star: which is a point that microtubule grow out of the centrosome
there would be a lot of material including monomers of the tublin
and 2 structures which is a pair of centriole which is a unique form of mictotubials
you'll see 3 microtubials hollow tubes (the pair) and 9 of them will form each centriol
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a lot of decorative proteins similar to actin filament
cleavage of the microtubial or
stablising
spacing microtubule in a parallel structure with a tighter gap versus a little bit of gap
cross linking proteins
motor protein for actin filament= Myosine
microtubule has 2 motor proteins
one is Kinesin
theother one is Dynein
kinesin always moves things to plus end
has 2 heads and based on the ATP hydrolysis
they make binding to micro tubial and release when ATP is hydrolysing to ADP and inorganic phosphate
releasing of inorganic phosphate makes power stroke
Dynein always move things to minus end
if we want to move things to peryphery which one do you need to use?
kinesin
some exceptions some kinesins move towards minus end
in video some of the vesicles move towards a minus end and then suddenly u turn and go twards the plus end
how that u turn will happen? the vesicle is on dynein or kinesin how to change direction
change in motor protein
vesicle does NOT have limitation on how many motor proteins they can bind to
some vesicles have both dynein and kinesin binding sides so they could have kinesin and dynein
from whatever signal they get if they want to go to plus end they go with kinesin
but with another signal they disconnct the binding to the microtubial use dynein to bind ti the microtubule which will make the movement towards minus end
the picture shows how nerve sells which are usually very long use microtubule to transport vesivles
we have got a single hollow microtubule
as well as nine pairs of triplets micro tubules which form cemtriols and we have other ones
so we have 9+2 arrangements usually find in the cilia or flagella which make the motility
the way they make motility is that they make connection between pairs
that is usually bound with all sorts of dynein as well as linking protein which will hold the 2 pairs of microtubule
when we got ATP comming in
dynein will move the vesicle on the right hand side to minus end
force generation
having linking protein
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NOT having linking protein (having exposed to the proteolytic enzyme trypsin)
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7 intermediate filament
actin filament and microtubial: helical structure
intermediate filament: rope like structure
alpha helical monomer which will coil with another monomer
caled coiled- coil dimer
coiled- coil dimer will form tetramer
as 4 monomer and 8 of them will form 8 tetramer
forms the basis odf intermediate filament
cytoplasmic intermediate filament usually seen as a meshed network
microtubule : a lot of hairs coming out of centre which is centrosome
INTERMEDIATE FILAMENT does not really have a centre
they are usually a mesh network
the table shows the major types of intermediate filament in the cells
the most famous one is a nuclear lamina made of lamin A , B and
C
nuclear lamina will give a mechanical structure forces for the nucleus
for spesific tissue type
vimentin
desmin
interface between cytoplasm and nucleus
nuclear por in nuclear envelop
actin in red
microtubule in green
intermediate filament the one in the nucleus: nuclear lamina
they all interconnecter to eachother through the protein complexes and they all work together rather than doing a job very separately
in the interface of nucleus a lot of them connected to eachother