Protein Transport II (Lecture 13) Flashcards
True or False: Matrix targeting sequences LACK negatively charged (Asp, Glu) amino acids
True
How are proteins imported into mitochondrial matrix?
Precursor proteins synthesized on cytosolic ribosomes
Polypeptide kept unfolded by chaperones (Cytosolic Hsp70)
MTS binds to outer membrane import receptor near a rare “contact site” with the inner membrane
MTS inserted into translocon of the outer membrane (Tom)
Translocating protein moves through Tom and inserts into translocon of the inner membrane (Tim)
MTS removed by a matrix protease
Hsp70 ATP hydrolysis releases newly imported protein
Protein folds into its mature, active conformation within the matrix
What are the three energy inputs required for mitochondrial matrix import?
Cytosolic Hsp70
Matrix Hsp70 anchored to the Tim44 protein
Analogous to BiP and Sec63 of post- translational translocation into ER
H+ electrochemical gradient (proton- motive force) across the inner membrane
True or False: Proteins must be unfolded to translocate!
True
True or False: Path A is
analogous to type-I membrane proteins inserted in ER membrane
True
Path B contains ______ sequence
Oxa1-targeting
True or False: Path C does not have MTS.
True
True or False: Many mitochondrial outer membrane proteins have a β-barrel structure
True
What structure inserts β-barrel proteins into the outer membrane?
sorting and assembly machinery
(SAM) complex
The ______ in chloroplast contain enzymes that help fix CO2.
Stroma
True or False: Import of proteins into the
stroma is similar to import
into the mitochondrial
matrix
True
______ are internal interconnected membranous sacs that contain all the enzymes for photosynthesis
Thylakoids
SRP-Depedent pathway
Same as post translational translcation but (SecY instead of Sec61)
pH Dependant pathway
Folded and bound to cofactor in stroma
Tat (twin-arginine translocation) pathway:
Thylakoid-targeting sequence must have two closely spaced Arg residues
Tat proteins oligomerize in membrane to create pores of variable size to accommodate folded protein
Powered by electrochemical gradient across thylakoid membrane
Thylakoid-targeting sequence is cleaved off
______ sequences direct post-translational transport of the unfolded proteins through translocons into the organelles
Targeting
______ contain enzymes that oxidize amino acids and fatty acids, breaking them down for biosynthetic pathways
Peroxizomes
True or False: Peroxisomes also contain catalase to
convert H2O2 into H2O
True
True or False: All lack DNA and ribosomes (unlike
mitochondria and chloroplasts)
True
True or False: Ubiquitination controls Pex5 recycling back into monomeric, soluble form in cytosol
True
Peroxisomal proteins
Requires a C-terminal Ser-Lys- Leu targeting sequence (PTS1)
PTS1 binds to Pex5 receptor
True or False: Peroxisomal membrane proteins are not targeted by PTS1 sequences
True, some (Pex3, Pex16) are placed in ER membrane
______ allow movement of mRNAs, tRNAs, ribosomal subunits out of nucleus
Nuclear pores
True or False: In nuclear pore complexes, Ions, small metabolites, proteins < 40 kDa can diffuse passively through NPCs (in or out)
True
FG-nucleoporins are:
Rich in hydrophobic Phe and Gly (F&G) residues (FG- repeats)
Line the channel of NPC and associated with nuclear basket and cytoplasmic filaments
Thought to form a gel-like matrix that allow diffusion of small molecules while excluding large ones
True or False: Import of nuclear proteins requires nuclear-localization signals
True
Targeting of nuclear proteins require ______, ______ and ______.
Nuclear-localization signal (NLS)
Ran
Nuclear transport receptor
