Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
39 Cards in this Set
- Front
- Back
|
ER lumen
|
ER cisternal space - created by the conformation of the nuclear membrane and the ER membrane
|
|
|
ER roles
|
lipid and protein biosynthesis
intracellular calcium storage production of all transmembrane proteins most of lipids glycosylation |
|
|
co-translational
|
translocation begins during translation
|
|
|
post-translational organelles
|
mitochondria
choroplasts nuclei peroxisoms |
|
|
transitional ER
|
areas of smooth ER from which transport vesicles carrying newly synthesized proteins and lipids bud from from transport to Golgi
|
|
|
smooth ER
|
lipid metabolism
steroid hormones detoxification |
|
|
calcium storage
|
release in response to extracellular signals
calcium pump transports calcium from the cytosol into the ER lumen, where high concentration of calcium binding proteins are locate |
|
|
lipoprotein particles
|
principle site of production in the hepatocyte, carrys lipids via the bloodstream to various parts of the body
|
|
|
microsomes
|
small closed vesicles formed when tissues disrupted, allows for isolation of ER
|
|
|
ER signal sequence
|
N terminal leader peptide attached to either transmembrane of water-soluble proteins entering ER
|
|
|
SRP
|
signal recognition particle
cycles between ER membrane and cytosol and binds signal sequence six different polypeptides bound to RNA molecule has hydrophobic binding site |
|
|
SRP receptor
|
located in ER membrane
|
|
|
mechanism of SRP
|
large rod like structure
-binds ER signal sequence -blocks elongation factor binding site therefore stopping translation |
|
|
safety of "pause" in translation (two)
|
-ensures no release into cytoplasm, unwanted potentially harmful
-inhibits folding which could hinder entrance into ER |
|
|
membrane-bound ribosomes
|
attached to the cytosolic side of the ER membrane and engaged in the synthesis of proteins that are being concurrently translocated into ER
|
|
|
free ribosomes
|
unattached to any membrane, synthesize all other proteins encoded by nuclear genome
|
|
|
polyribosome
|
attached to the ER, directed there by the signal sequences on multiple growing polypeptides
and ribosome can attach mRNA, mRNA remains permanently bound to the ER as part of ribosome, individual ribosomes can cycle back to cytosol |
|
|
Sec61 complex
|
water filled pore through which the polypeptide passes through the membrane
|
|
|
BiP
|
binding protein
used for post translation translocation across ER membrane |
|
|
post translational translocation
|
proteins first released into cytosol
interaction with chaperone proteins to prevent folding interaction between BiP and Sec61 complex repeated binding and un-binding of BiP protein causes unidirectional translocation of protein across membrane |
|
|
start-transfer signal
|
signal sequence binds specific site in translocator after sufficent length thereby opening the pore
thus ER signal sequence binds SRP and then acts as start transfer by binding pore after complete translocation of protein, signal sequence causes lateral gating where it remains to be degraded can also be internal |
|
|
stop transfer signal
|
additional hydrophobic segment stops the transfer process causes lateral gating and incorporation into membrane with N terminus on lumenal side and C terminus on cytosolic side
|
|
|
internal start - transfer fate of protein
|
can be oriented in one of two ways thus C terminus can be either lumenal or cytosolic
|
|
|
multipass membrane proteins
|
polypeptide chain passes back and forth repeatedly across the lipid bilayer
thought that internal start transfers serve as initation of translocation |
|
|
multipass membrane protein start vs stop
|
mainly based on position relative to polypeptide, SRP begins scanning from N terminus and proceeds to C terminus until recognition of first appropriate hydrophobic patch
|
|
|
orientation in membrane
|
all proteins inserted from cytosolic side
thus all copies of same chain will have same orientation - asymmetrical ER membrane thus insertion into ER determined orientation in all proceeding membranes |
|
|
ER resident proteins
|
contain ER retention signal
|
|
|
protein disulfide isomerase
|
PDI
ER resident protein catalyzes the oxidation of free sulfhydryl groups on cysteines to form disulfide bonds |
|
|
S-S bonds (prevalence within the cell)
|
almost all proteins exposed to lumenal face or extracellular space are disulfide bonded
form only rarely in cytosol due to reducing environment |
|
|
precursor oligosaccharide
|
N-acetylglucosamine
mannose glucose containing 14 sugars total transfered en bloc to proteins in the ER |
|
|
N- linked
|
precursor protein is transferred to amino group in asparagine
three glucose and one mannose removed rapidly |
|
|
oligosaccharide transferase
|
active side on lumenal side of ER, hence cytosolic proteins are not glycosylated in this manner
en bloc transfer of oligosaccharide linked through high energy pyrophosphate bond which provides energy for reaction |
|
|
dolichol
|
special lipid molecule which holds precursor oligosaccharide in place in ER membrane
|
|
|
O- linked oligosaccharides
|
linked to hydroxyl group side chain of a serine, threonine or hydroxylysine
|
|
|
calnexin and calreticulin
|
ER chaperone proteins require calcium for activity
oligosaccharide needed for proper folding bind to N-linked one glucose |
|
|
glucosyl transferase
|
adds one glucose (interaction with calnexin and calreticulin) to oligosaccharides attached to unfolded proteins only
|
|
|
dislocation
|
retrotranslocation involving the movement from ER to cytosol for degradtion
|
|
|
unfolded protein response
|
when concentration of unfolded proteins rise, genes transcriping ER chaperone proteins, retrotranslocation, and protein degradation in cytosol are up regulated
|
|
|
GDI anchor attachment
|
ER lumen
attachment to C terminus destined for the plasma membrane |
