SEEGAR Flashcards
Proteins that are destined for secretion or insertion into cellular membranes are synthesized in the __________________.
Endoplasmic Reticulum (ER)
Each protein contains a _________ element in its primary sequence that directs it to the correct organelle.
targeting
____________ is the process of moving a protein across a membrane.
Translocation
Translocation is energetically coupled to minimize ______________.
reverse translocation
The ER signal sequence is typically located near the _________________ of the protein.
amino-terminus
The ER signal sequence is often ______ during translocation into the ER.
cleaved
The ER signal sequence is composed largely of __________ residues.
hydrophobic
Attaching an ER signal sequence to a protein that is not normally secreted will direct it to the ____.
ER
The ______________________ recognizes the ER signal sequence and directs the ribosome to the ER membrane.
Signal Recognition Particle (SRP)
The SRP receptor (SR) is a heterodimeric transmembrane protein localized to the ____ that recognizes the SRP-Ribosome.
ER
The interaction between SRP and SR is dependent on ___ hydrolysis.
GTP
Binding of the SRP to the ribosome causes a ____ in translation.
pause
The ____ is a gated ER pore that facilitates transport of the nascent polypeptide across the ER membrane.
Sec61 translocan
_______ is the core subunit of the Sec61 translocon.
Sec61α
Binding of the signal sequence to the Sec61 translocon causes the _____________ to open, allowing the polypeptide to enter the ER lumen.
pore
The ___________________ cleaves the ER signal sequence from the protein.
ER signal peptidase
The active site of the ER signal peptidase prefers ______________ residues in the P1 and P3 positions.
small hydrophobic
________________________ occurs when a protein is translocated into the ER after translation is complete.
Post-translational translocation
___, an Hsp70 family chaperone, binds to the unfolded translocating polypeptide to facilitate protein folding.
BiP
BiP binding and protein folding are dependent on ___ hydrolysis.
ATP
_________________________ span the membrane once and have their N-terminus in the ER lumen and their C-terminus in the cytosol.
Type-I transmembrane proteins
_________________________ have their N-terminus in the cytosol and their C-terminus in the ER lumen.
Type-II transmembrane proteins
_________________________ are similar to Type-II proteins, but their signal-anchor sequence is closer to the N-terminus.
Type-III transmembrane proteins
_________________________ span the membrane multiple times, with alternating orientations of their N- and C-termini.
Type-IV transmembrane proteins
_________________________ acts both as an ER signal sequence and a membrane anchor.
Signal-anchor sequence
A _________________________ is a stretch of hydrophobic amino acids that halts translocation and anchors the protein in the membrane.
stop-transfer anchor sequence
_________________________ are inserted into the ER membrane after translation is complete.
Tail-anchored proteins
The ___ complex recognizes the exposed hydrophobic transmembrane α-helix at the C-terminus of tail-anchored proteins.
Get3
___-dependent dimerization of Get3 is required for tail-anchored protein insertion.
ATP
____ and ____ are ER membrane proteins that interact with Get3 to facilitate tail-anchored protein insertion.
Get1, Get2
_________________________ are attached to the cell membrane via a GPI anchor.
GPI-anchored proteins
The _________________________ is responsible for attaching GPI anchors to proteins.
GPI transamidase complex
The GPI transamidase complex is a ___________ that cleaves the protein and attaches it to the GPI anchor.
Cys-protease
_________________________ can be used to predict the transmembrane domains of a protein.
Hydropathy profiles
Protein trafficking within a cell is determined by _________________________.
targeting and signaling sequences
Proteins in the ER undergo _________________________ to promote proper folding.
post-translational processing and/or modification
True or False: All proteins synthesized in the ER are secreted from the cell.
False. Some proteins synthesized in the ER are retained within the ER or transported to other organelles.
True or False: The SRP binds to the ribosome and the ER signal sequence simultaneously.
True
True or False: The Sec61 translocon is a passive channel that allows proteins to freely diffuse across the ER membrane.
False. The Sec61 translocon is a gated channel that requires energy for protein translocation.
True or False: Glycosylation is a common post-translational modification that occurs in the ER.
True
To move a protein across a bilayer, proteins are typically __________.
unfolded
GPI stands for ________.
Glycosylphosphatidylinositol
