Module 9 Flashcards
Protein insertion into the mammalian ER membrane is typically
cotranslational.
Signal sequences that direct proteins to the ER membrane are:
Stretches of hydrophobic amino acids located generally located near the amino terminus of the protein
___________ provides the driving force for translocating a polypeptide chain into the ER post-translationally.
ATP hydrolysis by BiP
N-linked oligosaccharides are:
Added in the ER and modified in the Golgi
GPI anchored membrane proteins are membrane associated by
a covalently attached lipid.
The topology of membrane proteins can often be predicted by computer programs that identify ________________________________________ topogenic segments.
hydrophobic
During N-glycosylation of proteins, an oligosaccharide precursor is first synthesized with _______sugar residue (s) and this preformed precursor is later transferred to the nascent polypeptide chain.
14
Which of the following is a lectin?
calnexin
Proteins that do not fold properly in the ER lumen are degraded in the cytosol by
the proteasome.
Sorting of protein to mitochondria is
post-translational.
Tom/Tim protein complexes are involved in
protein translocation into mitochondria.
Sequences that target proteins to mitochondria are located at
the N-terminus of the precursor protein.
Protein import into the mitochondrial matrix is supported by energy input from
ATP hydrolysis by chaperone proteins in the cytosol.
ATP hydrolysis by chaperone proteins in the mitochondrial matrix.
the proton-motive force across the inner mitochondrial membrane.
Many peroxisomal matrix proteins are imported as
folded proteins.
The nuclear pore complex allows for
passive diffusion of smaller molecules, import of proteins, active transport of very large molecules
The nuclear transport receptor can bind to:
FG nucleoporins, Ran·GTP, basic nuclear localization signals in cargo proteins
Which of the following is true about targeting of a secretory proteins?
The signal recognition particle (SRP) binds to the signal peptide soon after it appears outside the ribosome.
The amino acid sequences that target proteins to chloroplasts, mitochondria and nuclei have the following property in common:
When added in the proper context, they are sufficient to direct the targeting of a foreign proteins into the respective organelles
Glycosylation of proteins inside the endoplasmic reticulum does not involve:
a His residue on the protein.
ER Type-I transmembrane proteins possess all of the following :
cleavable signal sequence, internal signal-anchor sequence, internal stop-transfer sequence
Elucidate three different pathways for targeting proteins to the mitochondrial inner membrane.
inner membrane single pass, matrix, inner membrane multipass
What is the meaning of “quality control in the ER?” Describe the unfolded-protein response. What is the fate of unassembled or misfolded proteins present in the ER?
BiP -> Ire1 -> Hac1 upregulate chaperones
Describe the typical principles used to identify topogenic sequences within proteins and how these can be used to develop computer algorithms. How does the identification of topogenic sequences lead to prediction of the membrane arrangement of a multipass protein? What is the importance of the arrangement of positive charges relative to the membrane orientation of a signal anchor sequence?
Hydrophobicity determines membrane spanning-region, positive charge indicates cytosolic side of stop-transfer sequence
List the post-translational modifications that occur in the ER. Why are bacteria often a poor choice for the production of proteins for therapeutic purposes?
Glycosylation, Disulfide isomerase and chaperone folding, cleavage
To what extent do peroxisomal matrix protein import and peroxisomal membrane protein import share the same machinery?
Come from nuclear transcripts, but recognized and translocated by different proteins
In multipass membrane proteins synthesized in association with membrane-bounded ribosomes of the rough ER, signal-anchor and stop-transfer anchor sequences alternate. What do these sequences do? Compare and contrast Type I, Type II and Type III ER membrane proteins.
type 1: signal sequence at amino end that is cleaved off, stop transfer designates cytosolic side
type 2: not cleaved, translocated from signal-anchor, C is in lumen, N is in cytosol
type 3: not cleaved, signal anchor, N in lumen, C in cytosol
