Chapter 12: Intracellular Sorting Flashcards
about what percentage of cell volume is typically consisting of the cytosol?
~50%
about what percentage of cell volume consists of the mitochondria?
~22%
This is true if the transport of a molecule to another area does not require transport through a membrane.
Topological equivalence
the nucleus is topologically equivalent to what?
the cytoplasm
The ER is topologically equivalent to what?
membrane-bound organelles, vesicles, extracellular space
What are 3 type of intermembrane transporters?
- gated transport
- transmembrane transport
- vesicular transport
where in the cell does gated transport typically occur?
cytosol –> nucleus
Where in the cell does transmembrane transport occur?
cytosol –> mitochondria, plastids, peroxisomes
Where in the cell does vesicular transport occur?
membrane-bound organelles –> other membrane-bound organelles
This type of transport uses budding and fusion mechanisms to transport soluble/membrane-bound molecules
vesicular transport
Where do all membranes come from?
pre-existing membranes
nuclear DNA is not _____ for a living organism
adequate
What information (in addition to nuclear DNA) is required for life?
- asymmetry info
- structural info
a membrane-bound organelle that is continuous with the nuclear envelope that focuses primarily on protein synthesis
rough ER
a membrane-bound organelle that is continuous with the nuclear envelope that focuses primarily on lipid metabolism and toxicant management
smooth ER
this is an outer membrane structure of the nucleoporins that recognize nuclear localization signals
cytosolic fibrils
this is an inner membrane structure of nucleoporins that conducts “quality control” on molecules, proteins, mRNA that must exit into the cytosol
nuclear basket
the intermembrane structure of nucleoporins
membrane ring proteins
This type of transport relies on active GTP, G-protein coupled receptors to import/export things from/to the cytosol
nuclear import + export
What are 5 transmembrane transport proteins found in the mitochondria?
- TOM Complex
- SAM Complex
- TIM22 Complex
- TIM23 Complex
- OXA Complex
This transmembrane transport protein complex recognizes cytosolic proteins tagged with mitochondrial signal sequences; then pulls in protein to matrix
TOM complex
How is TIM23 different from TIM22
TIM23 = multifold proteins
This transmembrane protein passes protein through the second mitochondrial membrane into the matrix from
TIM23 complex
What happens to any translocative signal sequences after the protein reaches its desired loaction
cleaved off
What proteins are required to facilitate the transmembrane transport of a protein through TOM/TOC proteins?
hsp70 chaperones
Energy-dependant conformational changes in import ATPases occur one which transmembrane transport protein?
TIM/TIC
What is different about transmembrane transport to chloroplasts vs. mitochondria?
- uses TOC/TIC proteins
- has additional thylakoid space
When present, this signal sequence tends to be exposed after the chloroplast signal sequence is cleaved off
thylakoid signal sequence
What are two types of ER signals for ER-targeted proteins?
- co-translational translocation
- post-translational translocation
This type of rough ER signal occurs when a growing peptide chain reveals an ER-targeting signal sequence to associate ribosomes to the ER membrane before resuming translation
co-translational translocation
This type of ER signal occurs when a completely synthesized polypeptide chain/protein associates with the ER membrane via and ER-targeting signal sequence
post-translational translocation
This is a receptor that binds to ER-targeted signal sequences to associate ribosomes with the ER
SRP (signal recognition particle)
This protein removes the signal sequence from the ER-targeted protein after translation/translocation is complete
signal peptidase
This protein recognizes the ER-targeted signal sequence in a protein to aid in integration/translocation
protein translocator
In co-translational translocation, polypeptide translation resumes after what step?
SRP removal
This sequence is found in membrane-associated/integrated ER-targeted proteins that indicates when to stop the “pull through” action
stop-transfer sequence
In regards to membrane-associated/integrated proteins, what determines the cytosolic vs lumen portions of the protein?
stop-transfer sequence charge orientation
The positive end of the stop-transfer sequence is located where?
cytosol
What three proteins in the ER all guide misfolded proteins out of the ER lumen?
- lectin
- chaperone
- disulfide isomerase
Where are misfolded ER lumen proteins guided to?
protein translocator complex
What happens as a misfolded ER lumen protein is removed from the ER lumen?
tagged with polyubiquitin chain –> guided to proteosome –> digested
What is the fate of a misfolded ER lumen protein?
proteosome digestion (NO rescue)
What are the 3 sensors for misfolded proteins in the ER lumen?
- IRE1
- PERK
- ATF6
What are the most common stressors that induce HSP chaperone activity?
- heat
- pH
- [O2]
What are the results of increased misfolded ER lumen protein sensor activity?
- upregulation of HSP70
- translocation slowing
- translation slowing
An enzyme associated with the ER phospholipid bilayer that encourages symmetrical growth of the membrane
scramblase
An enzyme associated with a cell’s plasma membrane that encourages the asymmetrical, cytosolic monolayer after integrating exocytotic membranes
flippase
New phospholipids are added to what side of the ER membrane?
cytosolic portion
