2.2 - Organelle + Gated Transport Flashcards
Hsc
cytosolic chaperone protein
- maintains proteins that have been translate with cytosolic ribosomes in unfolded state
TOM 20/22
import receptor
what drives import into the mitochondrial matrix
mitochondrial matrix Hsc70 (chaperone protein) and ATP hydrolysis
what are contact sites
areas where the mitochondrial outer and inner membrane are close to each other
TOM
import receptor and translocator for mitochondrial outer membrane
TIM
imporer translocator for mitochondrial inner membrane
mitochondrial targeting sequence chemical characteristics
moderately amphipathic
what is the mitochondrial targeting sequence recognized by
protein-protein interaction by a signal receptor on the TOM complex
how does TOM complex integrate porins into the lipid bilayer from the outside
it doesn’t, can’t integrate porins into the lipid bilayer from the outside directly
how are porins integrated into the mitochondrial outer membrane
1) porins first transported into intermembrane space
2) binding to specialized chaperones
3) porins bind to SAM complex
4) SAM complex inserts them into outer membrane
BAM
similar to SAM complex, bacterial outer membrane that inserts b-barrel proteins into bacterial outer membrane in gram-negative bacteria
what is one piece of evidence that supports the endosymbiotic origin of mitochondria
the central subunit of the SAM complex is homologous to the BAM complex in bacteria
translocation method for chloroplast proteins
post-translation translocation
compare the import signal sequence of chloroplast to that of mitochondria
similar
TOC
import receptor and translocator for chloroplast outer membrane
TIC
import receptor and translocator for chloroplast inner membrane
where is the photosynthetic system located in chloroplast
thylakoid membrane
what is the thylakoid signal sequence located relative to the chloroplast signal sequence
located after
transport of thylakoid precursor proteins steps (2)
1) pass through double membrane system if chloroplast at specific contact sites
2) translocate into thylakoid membrane via system similar to SRP and SecYEG
peroxisomes function
site for fatty acid oxidation
peroxisomes method of translocation
post-translational translocation
peroxisomes structure
single membrane organelle
peroxisomes import signal
short sequence at C-terminus
- S K L
peroxins
proteins that participate in import process into the peroxisome (very poorly understood_
Zellweger syndrome
inherited disease caused by defect in importing proteins into peroxisomes (brain abnormality and death after birth)
primary hyperoxaluria
inherited disease which peroxisome signal sequence of alanine:glyoxylate aminotransferase is altered
- protein mislocalized to mitochondria and can perform normal function
nuclear envelope
double-membrane structure that encloses DNA and defines border of the nucleus
- has pores
nuclear envelope exported products
1) tRNA’s
2) mRNA’s
nuclear envelope imported products
1) histones
2) DNA/RNA polymerases
3) gene regulatory proteins
4) RNA-processing proteins
NPC
nuclear pore complex
- perforate the nuclear envelope
fibrils
NPC proteins that form disordered tangle to restrict permeability
FG nucleoporins
called this because fibrils are made of repeating Phenylalanine-glycine residues
what is the cut off for proteins that cannot enter the nucleus via passive diffusion
larger than 60 kDa
NLS
nuclear localization signal for nuclear import
- short sequence of positively charge K and R
- located anywhere on the protein (not important)
can fully folded proteins be transported through an NPC
yes
importin
proteins that carry cargo proteins that transport the cargo protein.
- binds to NLS and NPC proteins
GTP-Ran
complex that binds onto the importin to release the cargo protein
GTP on GTP-Ran function
acts as a timer
- when GTP hydrolyzes (slow hydrolysis), the Ran switches conformation and dissociates from the importin
Ran on GTP-Ran stands for…
Ras-related nuclear protein
where does Ran-GTP bind to the importin
binds to importin on nuclear side of pore (causes receptors to release cargo)
what happens the the Importin with Ran-GTP after the cargo is released
transported back to cytosol
how does Ran-GTP dissociate from the importin
GTP is hydrolyzed and converted to Ran-GDP
how does export of nuclear proteins work
1) Free export receptors go into nucleus
2) Ran-GTP in nucleus promotes cargo binding to the export receptor
3) interaction with fibrils transports the complex to the cytosol
4) hydrolysis of Ran-GTP releases the export receptor and the cargo
5) export receptor returns to the nucleus
