Please enable JavaScript.
Coggle requires JavaScript to display documents.
L35_cellular Protein trafficking and secretion_oct 25 (8- ER…
L35_cellular Protein trafficking and secretion_oct 25
1-secretion: exocytosis
how we produce proteins? proteins are all produced in ribosomes. how we get proteins from ribosomes to the many different areas of the cell where all these proteins are going to function
a lot of cells are highly specialised to exocytosis
a lot of hormons are protein based, they get produced by ribosomes, they get trafficed to the cell membrane and they get vomited into the extra cellular fluid and eventually end up in blood
nuclear bilayer is continueus joined with endoplasmic reticulum
biochemical messengers are secreted from the cells and vast majority of these thend to be proteins
vomitted in the blood stream
pumped around
get to the receptor somewhere
there are receptors that are inside our cytoplasm
when activated can translocate into the nucleus
something is regulating the step betw sth being in the cytoplasm and sth entering the nucleus to effect DNA
1 more item...
mRNA being transcribed
mRNA binding to a ribosome
ribosome inducing translation
poly peptide becomes a protein
in vesicles they shuttled around in vesicles and that can ejected into extracellular fluid
this is the process of exocytosis
2- Proteins are produced by ribosomes
2 places that we can find ribosomes
locations that we can produce protein
1- rough endoplasmic reticulum
2- free in the cytoplasm
proteins are everywhere in the cell
3- How can proteins be delivered to their
appropriate destinations?
prot. have post codes called signal sequences :star:
signal sequences are short
4 -6 amino acids
in different locations in the protein
post codes tell the cellular machinary where to deliver that protein to
target proteins in nucleus
lack of sig. seq. acuumulating of pr. in cyto.
sig seq for mitochondrion/ chloroplast/ ER
if you have got nuclear localisation signal
you can be imported into the nucleus (you dont have to)
coloured amino acids are essential
produce transgenic proteins
we stick nuclear localisation sig. on any pro.
when we have the full seq.
that protein is only expressed in the nuclei of the cells
by florecent proteins we have florecent nuclei of our cells
you mutate one of the lys
the protein still produced
still a florecent protein
but it is in the cytoplasm of the cells
we have the shadow of nuclei
so it is not becoming imported into the nucleus
1 more item...
90 000 cellular proteins
how to find their correct cellular location?
do not memorise seq.
different seq for different cellular localization
sig= post codes to go to specific location and very specific
4- Protein Destinations nucleus
Nuclear localization signal (NLS)
NLS can be anywhere in a protein
caboxy terminal functional domain or you might need an amino terminal functional domain
Nucleus signal can be anywhere
can sit somewhere where ther is not a functional domain
nuclear proteins get translated by ribosomes that are free in the cytoplasm
not normally translated on the rough ER
they get imported across the nuclear bilayer via nuclear pore complex :star:
interaction with a lot of import signals with the nuclear pore complex governs what get included and what get excluded from import process
it is a regulated process
Import & Export via Nuclear Pore Complexes (NPCs)
you cant get through nuclear bilayer
unless you are steroid hormon
bigger than that which is protein
limited to go into nuclear pores
nuclear pores are huge multi protein complex
so big that if you freez fracture of cell
you can see them by electro microscopy
1 more item...
proteins to get into the nucleus it has to bind to nuclear import receptor = Importin
after we bound to the nuclear import receptor
the entire the entire complex can freely be transported cross the nuclear pore complex
for the complex to dissociate to let go of the protein that has just dragged into the nuclus
Ran- GTP :star:
another signalling molec.
binds to the nuclear import receptor
allows it to letgo of its cargo
sufficient amount of Ran GTP signalling molecules inside cells
continue delivering all of their nuclear cargo (proteins)
1 more item...
recycling receptor
after receptor lost its cargo goes back
bind again to the nuclear pore complex
get trans-located to the outside
we will be agble to reuse nuclear receptors to get more proteins into the nucleus
we have to dissociate the Ran GTP
1 more item...
we have prot. with nuclear export sig.=NES :star:
to leave the nucleus
we have got nucleur export receptor
bind to our protein while bound to Ran GTP
translocates through the nuclear pore
1 more item...
quite common for proteins to have an export signal and an import signal
protein can be shuttled into and out of the nucleus
most of them is regulated by GTPase activating protein levels =GAP
5- Protein Destinations: mitochondria (or plastid)
we dont have mitochondrial pore complexes
not big open doors that we can go through
we have 2 discrete membranes
we can get through the first membrane
get stock in between the 2 membranes
the process is similar to both of those memb.
but different proteins to transport across diff membranes
start synthesising our proteins on our ribosomes that are free in cytoplasm
mitochodrial signa. have to be located in the amino terminal in our protein
meaning: they translated first
1 more item...
we need to transit across another memb.
6- Translocation into Mitochondria is via TOM/TIM Protein Translocators
mt Localisation signal will translocate to the transporter outer memb. complex (TOM)
poke through and get treaded to the inner memb. complex
inner memb. complex has an ATPase
it can burn energy so that pull the pro. to the rest of the way through
feeded through the first bit and fed through the second bit and we burn ATP to go into the matrix space of the mt
a lot of proteins imp for mt func. that are inserted into the outer memb. or inner memb.
ATPase is necessary for ATP phosphorylation
we need protein complexes that are passing the protein through
we need insertion complexes that inserts proteins into the outer memb. = SAM = sorting and assembly machinary
we have separate insertion complex
that insert proteins into inner memb.= oxidase activity because it is also an oxidase. it doesnt oxidise the pro. when they are being inserted in the inner memb. wired numenclucure
we can get inserted into TOM complex
1- treaded into outer memb.
2-go through our TIM complex then inserted into inner memb.
or we can go throu both and end up in the matrix space of mt
proteins are produced and bound to chaperons
the signal seq binds to the TOM complex
moves around and gets translocated
lines up the signal seq. in the protein
1 more item...
7- Protein Destinations: secretion or membrane= exocytosis
exocytosis has got a lot of different parts to it
prodicing pro. on a robosome
robosome translocation to rough endoplasmic retic
robosome on ER are not attached they start off floating around in cytoplasm when they start producing pro. they translocate to the ER >>> ER is now called rough
each one of the pro. are like mt localisation signal
we have to have signal seq. right at the amino terminal it has to be the first thing produced
we can then target our mt to the endoplasmic reticulum
we produce our signal first : essential
when we get to the end of the signal, translation get paused
it stops when a ribosome (poly robosome) and its associated mRNA protein being translocated into ER
it binds to transporters on endoplasmic reticulum
1 more item...
8- ER translation/translocation
we begin translation in the cytoplasm
green: ribosome
red: begining of protein translate a single peptide
as soon as the single peptide is produced the whole thing stops
because we need the binding of signal recognition particle SRP :star:
that is a protein recognising the endoplasmic ret. sig thats being translated on our protein
it binds to the ribosome and pauses translation
the whole thing get targetet to ER and SRP binds to a receptor that is present on the ER and next to that we have a protein channel called a prot. translocateor :star:
this complex then inserts the signal seq on pro. into protein translocator
we can begin translation again
takes the pause away
pro. get translated through the translocator
we have got a ribosome sitting on our prot. poking through our translocator and all of that holding a ribosome at the rough endoplasmic reticulum
1 more item...
exocytosis starts with ER and goes out to plasma memb.
endo cytosis : swallowing the proteins
wrapping the in visicles
transporting vesicles back to golgy aparatus where we can use or modify them
9-vesicles are not passive sacks
vesicles have lots of proteins . lots of these pro. have diverse functions
one thing is telling vesicles where to go
Rap proteins tell vesicles where to go :!?:
10a sort of vesicle that has neurotransmitters
they have pumps and secondary active transporters
SNARE :star:
are necessary for allowing these vesicles to attach to where they need to get to
necessary for docking so you can unload your cargo
11- metabolism- Vesicles are assembled by coat proteins
their assembly is not random, they assemble because of a lot of control mechanism
in ER we have pr. that are translated in the ER
we know what we are assembling into vesicles
needs to be some sort of recognition of these proteins
normally this process kicks off by each one of our proteins binding a specific receptor that are present on ER
receptors gather together forming receptor bud
clatherin binds to that bud
these proteins form ekeleton, pinches off one of the vesicles
by mutating any of the steps you dont get vesicles being formed
coat or clathering proteins are necessary for assemply of the vesicles , but when the vesicles formed these get released as the vesicle matured
coat or clatherin proteins can then get recycled
1- in the first blace they make the vesicle bud off
2- they released from vesicles as it matures and goes to its destination
different coat proteins for different parts of the cell
tells us where they are come from or formed
they are necessary for formation
not necessary for targetting the pro. to any specific location
coat protein specific for ER = coat protein 2 :star: = COPII
coat protein specific for shuffling vesicles from the Golgy
apparatus back to the ER or suffling between different sisternea
in golgi apparatus= coat protein 1 :star:= COPI
clathrin :star: are formed part of the golgi apparatus then goes to the plasma memb. also formed by the plasma memb. when we get endo cytosis of these vesicles as well
12 - Rabs and SNAREs mediate docking & fusion
what targets the proteins to specific location is Rab protein
different Rab proteins and each one is specific in targeting pro. to a specific destination
Rab1 protein will target you to Golgi apparatus
these are the address
different Rab pro. if targeted to a diffe. dest. in the cell
they interact , tether your vesicle to a particular micro tubule or a particular Motor protein moving along the microtubule
kinesin, dynein and dysine which move along the micro tubule and micro filaments, each one can carry a visicle and the vesicle that it chooses to carry are the ones that have the specific Rab protein that they need
Rab proteins interact to motor proteins and thats how they get suttled to specific locations within the cell
SNAREs
SNARES tell you what you can actually attach to
different types of SNARES
v-SNAREs = vesicle snares
t- SNAREs= a type of SNARE that attach to the targer wherever the vesicle is going to bind
for exocytosis:
v- snare is on our vesicle
t-snare will be on the plasma membrane
if being re shuttled back to golgi apparatus
v SNARE on vesicle
t SNARE on the golgi apparatus
SNARE is like velcro (nari va medegi) the right combination of male and female velcro they will fuse and stick together
Rabs bind to motor proteins and attach to the network that actually delivers these vesicles and then when they get where they suppose to be
they get held by the membrane by the SNAREs
1 more item...
electro micrograph
initial docking of vesicle
next step 2 membranes fuse to each other
vesicluar mebrane will become part of the plasma memb.
ejection of the protein cargo into extra cellular fluid
13- Golgi apparatus
modification
golgi apparatus is not stacking of sacks that stay there for entire life- it is dynamic
you can look at the budying of vesicles from golgi apparatus
Golgi apparatus is directional
it has a cis face and a trans face
they do different thinks and have different types od the code protein - they are functionally different
what Golgi apparatus is dooing?
1- sorting all of our proteins
proteins that are produced from ER go straight to GA
1 more item...
14- Exocytosis can be constitutive or regulated
exocy. doesnt have to be a constituitive process
(not just happen) we can add in an extra regulatory step
they get everything ready to exocytosed and then pauses it
it stops and waits there waiting for signal
this is how nerves in body talk to each other
a type of exocytosis is constituitive
we translate our protein, move it to Golgi apparatus
modify if by sticking sugers on
bud off to another vesicle and vesicle goes to the v SNARE and t SNARE bind and vomits its cargo into extra cellular fluid
constituitive= it just happens
more commen is when we regulate it
we do all initial stuff
we produce our protein, modify it, and ship it twards plasma memb
when it gets to plasma memb its v SNARE and t SNARE interact and that is where it stops
we stop here until we get some other signal that allow fusion
producing neuro trasmitter and how nerves talk to eachother
we produce neuro transmitters or hormones
they get loaded in to vesicles
1 more item...
15- neurotransmission –regulated secretion
how neurotransmitters talk between 2 neurons
we produce neurotransmitter and load them into vesicles
vesicles get moved to the plasma mem
there v snares and t snears for a complex , dock together
we dont immediately get fusion
until we get biochemical trigger
in neurons this trigger is calcium
when our nerves fire, an action potential gets to the end of an axon , it opens a voltage gated calcium channel
1 more item...