Exam 2 - mod 5 Flashcards
cellular compartments
membrane enclosed organelles take up .5 volume of a eukaryotic cell and expand the total surface area 20-30 fold
increases area of cell 20-30 fold
topographically, the interior of the endomem system is equavalent to the
extracellular environment
-want proteins doing bizz of golgi to be in golgi
the inside of the endomem system becomes the outside
mfucntions of membrane enclosed compartments of a eukaryotic cell
cytosol - contains metabolic pathways (in protein synthesis and the cytoskeleton)
nucleus - contains genomes
ER - synthesize most lipids proteins for distribution to organelles and plasma mem
golgi - godication, sorting, packagins of porteins and lipids
lysosomes - intracellular degradation -hydrolyic enxymes
endosomes - sort endocytosed material
mitochondria - atp synthesis by oxidative phosphorylation
chloroplasts - atp synthesis and carbon fixation by photo synthesis
peroxisomes - oxidation of toxic molecules
mitochondria relative volume and number in mem enclosed organelles
lots of mitochondria
the golgi
cis golgi -recieves proteins and lipids from ER
trans golgi - where proteins leave
transport vesicles around the outside, deals w packaging and sorting
further destination
protein sorting
requires signal sequences and specific receptor proteins
protein sequences some made in cytosol some in ER
transported into organalles by 3 mech
1 transport through nuclear pores
2 transport across membranes
3 transport by vesicles
2 protein synthesis process
free ribosomes
-nuclear proteins
-chloroplast and mitochondrial proteins
-cytosolic proteins
no ER signal sequence - remains free in cytosol
ROUGH ER - mem bound ribosome cycle
-most integral mem proteins
secreted proteins
lipids
produce proteins for secretion or mem insertion - encoded with an ER signal sequence
Same riosomes can attach to er or stack up in line
polysomes can make actin or nuclear proteins
cells endomem system
nuclear membrane is part of system
aqueous pores conenct the nucleoplasm and cytoplasm
compartmentalize parts of protien synthesis
proteins in nucleus differ from thos in cytosol
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distinct completments of proteins are present in nucleus and cytoplasm
nuclear envelop
pores
lamina
condensed chromatin
transmission electron micrograph of nuclear mem
cytoskeletal network of
lamins provides mechanical support to the nuclear face of the mem and binding sites for chromatin
proteins enter/exit by nuclear pores on nuclear envelope
nuclear pores
complex architecture with central channel of approx 9nm
density acts as barrier for nuclear diffusion
also attached to the lamina to keep in place
nuclear mem
acts a barrier to latereral diffusion of membrane proteins from nuclear to cytoplasmic faces of ER mem
protein diffusion
proteins less than 40000 molecular weight diffuse freely through pores on own
larger molecules need carrier proteins and energy from GTP hydrolysis to pass through
pores can expand to diameter of 40 nm.
importins
nuclear transport receptors are recycled
proteins have nls for import and nes for export
sequence recog by recepotrs which brings material into nucleus
importins –> nuclear import receptors
exportants –> export proteins
import of proteins are regulated
by RAN - small GTP molecular binding protein
protein will bind to import - goes to port in high RAN gtp
release the protein
has helper proteins like RAN -GEF
GEF load gtp into
RAN in nucleus - dense high levels
gap hydrolyzeds gdp to gtp
hydrolyzes GTP once past pores and cytosol
regulated RAN GTPAase binds to importin
using a RAN gradient
nuclear localization signals NLS
have basic amino acids in a linear sequence
binds to importins
single importin transports multiple proteins
Summary of nuclear proteins sorting
proteins enter nucleus through pores
smaller than 40000 daltson diffuse freely
pores expand to allow passage of larger protein s
nuclear transport proteins importins regulate transport with NLS using energy from GTP exchange
proteins imported to mitochondria chloroplasts and nuclei
mit genomes encode small amounts of proteins - subunits of respiratory chain complexes - other subunits encoded by nuclear genes and mush be imported in mitochondria
TOM and TIM complexts tranpsort unfolded proteins across mem
nuclear encoded proteins synthesized w signal sequence + transproted to organelles in complexes w chaperone proteins (importins) GTP and GDP graident controls import
ER
more interconencted
where mem and secreted proteins occur
er makes contact w itself and other organelles like mitochondria
likely to deliver lipids
ER contact sites –> ER mitochondrial junctions between ER mem and mitochondrial outter mem - transfering lipids
has other contact sites too
integral mem protein synthesis
proteins destined for endomem system are cotranslationally imported into the ER
signal hypothesis - signal sequence
secreted and integral mem proteins
15-35 aa
6-15 non polar aa
co translatioonal
signal recog particle (SRP) binds to protein and brings to channels
7SRNA signal seq is cleavved and cut off
chaperone
glycocylation
every secreted protien ahs sugar on it
process of integral membrane protein synthesis
signal reco particle binds signal seq and translation slows or stops
complex docs with SRP receptor in ER
ribosome engaged with translocon - translation resumes
bringing ribosome to translocator
SRP is displaced for reuse
signal sequence cleaved and unfoldded protein passes through the translocon pore
as portein emerges chaperones bind to
structure of signal peptidase
h spc - a and spc -c
has bidning pocket : select for shape
membrane thinning : select for length
cleavage: ser-his-asp triad
not cut going into nuclease but can cut in mitochondrai
insertion of transmembrane protein
cytosol on one side
ER lumen on other
trans mem proteins
as signal translated
has ER signal equence
goes through translocator
man proteins have multiple pass domaisn
future transmem domains act as start transfer and stop transfer signals for mem proteins
inserted cotranslationally
glycosylation
almost all integral and secreted proteins are sugar coated
start in RER
role of glycosyltransferases
donor nucleotide sugars
diff glucosyltransferases in diff membrane compartments
synthesis of core liogosaccharaides in ER
glycosylation begins co translationally
always same 2 glucoses ancestral match
core is linked to asperagine
dolichol phosphate and isoprene units
core - acetylglucosamine 1 phsophate
mannose
glucose
trimming of 2 glucose
role of chaperone in proper folding
misfolded proteins activate ER sensor proteins
which prompts activation of chaperone genes
chaperones bind to protiens to proper fold
chaperone degrade after and er sensor returns to inactive
calnexin chaperone proteins folding cycle in the ER lumen
ER site of lipid biosynthesis
enzymes whose active sites face ER lumen
however, topologic problem so use flippases
–keep ps low on expolasmic leaflet
PE high in cytoplasmic leaflet
facilitates vesicle budding from ER and golgi
cholesterol synthesized there but not maintained at low levels
enzymes in ER
lipid movements within and between membranes
ER and golgi exchange vesicles and flipping lipids in and out
LTP
untethered lipid transfer protein moves lipids between bilayers
lipid transfer at a mem contact site
autoinhibited OSBP
ER golgi contact sites
add cholestrol and change orientation of lipids
movement of lipids across mem bilayers
flippase in ER
P4 type atpase
there is a gradient of lipids
in the mem along the secretory pathway
effects of lipids on bilayer thickness
sphinglipids sterols and glycerophospholipds
sphingomyelin make thicker
