lecture 9 Flashcards
Signal sequences that direct proteins to the correct compartment are
Encoded in the amino acid sequence of the protein
Transport of proteins into the ER occurs:
during translation of the protein
Which of the following proteins serves to stabilize the membrane of a transport vesicle during its formation:
Coat proteins
There are at least two suspected origins for the evolution of internal membrane compartments
plasma membrane invaginations(endomembrane system)
endosymbionts
(mitochondria and chloroplasts)
proteins must be sorted** by distinct processes that use different mechanisms and signals to
be able to go to diff. parts of the membrane
energy inputs are required to move proteins across ______and to deform and _____ or fuse membranes.
membranes, separate
A signal sequence that has a long chain of hydrophobic amino acids, followed by a few negativly charges A.a at n termanus would be imported
into the ER
A signal sequence that has + charded A.a then - charged a.a then a hydrophobic A.a at the C ternimis would be
be in the lumen of the ER
A signal sequence that has + charged a.a thta are dispersed in the sequence near the N terminus would be
inported in to the mitochondria
A signal sequence that has a chain of + charged a.a would be
imported in the nucleus
A signal sequence that has hydrophobic a.a interdispersed in a section of sequence would be
exported from nuleus
a peroxiome has a signal sequence of
a single(very few) + charged a.a
Once proteins are transported into the _____ , they cannot be exported to the cytosol again
nucleus
Nuclear localization signals (NLS) receptors use
GTP hydrolysis
____ _____Complexes allow proteins and mRNAs to traffic across the nuclear membrane
nuclear pore
Classic experiment demonstrating nature of NLS
as a string of basic amino acids
used t-antigen
Proteins are —— as they are transferred
across the mitochondrial membrane
unfolded
signal sequence gets removed by _____ _____so this is unlike nuclear localization where shuttling can occur
signal peptidase
Mitochondrial signal sequence fro in to ______
an amphipathic alpha helix
Proteins being made can be directed for translocation into the ER by
Signal Recognition Particle (SRP) and the SRP receptor and a translocation channel
____ ____ of signal sequence bearing proteins into the ER membrane
Cotranslational insertion
Signal Recognition Particle associates with the nascent signal sequence, stalls the ribosome and aids _______________membrane at the SRP receptor
in docking on the ER
Proteins are modified by ______ in the ER and Golgi. _____ bond formation is also catalyzed inthe ER.
glycosylation, Disulfide
Chaperones are involved in
folding and proper membrane insertion in ER membrane
The N-terminal signal sequence of many secretory
proteins is cleaved off by a
signal peptidase
Start transfer and Stop transfer sequences specify insertion of ____ ______ ______ into the ER membrane
for single and multipass transmembrane domain proteins
hydrophobic transmembrane helices
_____ _____ ______ have helped to study the
nature of the signals, their recognition and import processes
Cell free reconstituted systems
Addition of ______ by oligosaccharide protein
transferases – note the high energy bond
glycosylations
Protein folding in the ER is monitored and assisted
by _____ ____before the mature proteins
are permitted to be ____ _____ of the ER
chaperone proteins. trafficked out
Unfolded Protein Response (UPR) a signaling pathway that helps cells maintain quality control over protein _____&_______by
increasing chaperone
activities.
folding and biogenesis
Cystic fibrosis is frequently caused by
misfolded proteins are rapidly degraded regardless of whether they are at all functional. in the ER
______ move soluble and membrane-associated proteins between cellular compartments
vesticles
secretory pathway vesicle transport has what stypes of flow
“forward” flow = ER ->Golgi -> Plasma Membrane ->Lysosome
-“retrograde” flow – e.g. Golgi -> ER “retrieval
Vesicles are formed and targeted by the action of
protein coats
Coats serve to deform membranes so that they can be “pinched off” by
dynamin – GTP hydrolysis
v-snares
are attached to the vesticle
tsnares
attach to the destination membranes
Rabs recognize _____ , then v-SNAREs and
t-SNAREs drive the fusion reaction and help provide membrane specificity
tethers
COP coated proteins
transport to the ER and golgi
The ____ face of the Golgi is a key sorting station as is the endosome
trans
Another experimental approach complementary to genetics
- in vitro
is using reconstituted protein sorting in cell extrac
Endocytosis of specific proteins, ligands, hormones and biomolecules can be
receptor-mediated
the early endosome is like the Golgi in that it
is a sorting point for different destinations
The pH of the lysosome is
Lower (more acidic) than the cytosol
Lysosomal function is important to sphingolipid degradation.
Problems in these different enzyme functions cause
lysosomal storage diseases
