Intracellular Compartments and Protein Sorting Flashcards
Hepatocyte
involved in detoxification
Rough ER
synthesis of soluble proteins for endomembrane
includes digestive/secreted enzymes
Smooth ER
phospholipid synthesis and detoxification
Organelles
structure in a cell that carries out particular function
most are membrane closed but they don’t have to be
What are membrane-enclosed organelles
Nucleus, ER, Golgi apparatus
non-membrane bound organelles
nucleolus, centrosomes
How are specific proteins sorted to different organelles
In the AA sequence, there is a specific sequence, sorting sequence that once recognized by sorting receptors, will move to their designated places
In what configuration are these proteins transported?
proteins that will be transported to the nucleus or peroxisome will be folded before they move to these compartments
Those going to the chloroplasts/ mitochondrion will remain unfolded as they move to these compartments
Proteins going to ER will move to lumen while the protein is still synthesizing
Post-Translational Sorting
- fully synthesized before transport
- Sorting receptors will recognize the sorting signals to move proteins to designated compartments
- Some proteins will be folded before transport while others will remain unfolded
Co-translational sorting
- occurs during translation
- proteins with ER signal sequence will go to ER
How do proteins move to nucleus
The protein will contain its sorting signal and attach to its sorting receptor, which will transport the protein through nuclear pores to the nucleus
How do proteins move into the peroxisome?
These enzymes detoxify toxins and get transported by transmembrane protein complexes
An import signal and the cargo will attach to the import receptor which passes through the peroxisomal membrane
How do proteins get sorted to mitochondria/chloroplasts
The protein will be surrounded by hsp70 chaperone proteins that will keep the protein unfolded and a sorting receptor that will move the protein mitochondria or cytosol where it will be folded after it has reached its destination
What is special about ER encoded sorting signal?
Its signal is a specific hydrophobic sequence
Why would proteins go to the ER
it is a direct entry to the endomembrane system
How does co-translation occur?
As the protein begins synthesis in the cytosol, the ER signal will be recognized and a temporary stop Codon will pause translation until the protein reaches the ER
What type of proteins will go to the ER
soluble and transmembrane proteins
Describe the process of co-translational translocation of soluble proteins
- Translation occurs, N-terminal ER signal sequence emerges
- Recognized by sorting receptor and the SRP will also recognize temporary stop codon and arrest translation
- SRP complex moves to translocon and opens
- Translation resumes and protein synthesis resumes in ER lumen
- ER sorting signal gets cleaved by signal peptidase and will be degraded
- Protein gets released into ER lumen and translocon closes
Describe co-translational translocation for transmembrane proteins
- Translation occurs, N-terminal ER signal sequence emerges
- Recognized by sorting receptor and the SRP will also recognize temporary stop codon and arrest translation
- SRP complex moves to translocon and opens
- Translation resumes and protein synthesis resumes in ER lumen
- ER sorting signal gets cleaved by signal peptidase and will be degraded
- stop-transfer sequence (a-helix) enters translocon
- protein transfer stops and transmembrane domain released into lipid bilayer (final protein dispensed across bilayer)
- Signal peptidase cleaves ER signal and translocon closes
Differentiate between N-terminus ER signal and internal ER signal sequence
N SS will have its signal on the N-terminus and is degraded
The internal SS will have a start transfer sequence and is not removed, remaining part of the protein
What does the orientation of internal start-transfer sequence depend on?
on either side of internal start-transfer, it will be positive/ negative and when the signal goes to translocon, the orientation will depend on where the polarity lies, the side that is more negative will go to ER lumen
What forms the endomembrane system
ER, golgi apparatus, endosomes, lysosomes
what do intracellular compartments exchange?
lipids and proteins
describe the secretory pathway
- proteins made in ER
- delivered to outside of cell (exocytosis)
- ER to lysosomes by endosomes
what is a vesicle
small, membrane-enclosed organelle in cytoplasm
shuttles components back and forth in the endomembrane system
What is the difference between constitutive and regulated exocytosis pathway
C will continuously delivering lipids and proteins (collagen)
R will have specialized cells in the vesicles and will stay in there until a specific signal is given to move
describe the path of secreted protein from translation to plasma membrane
- translation starts in cytosol
- ER signal gets recognized and moved to ER
- Co-translational translocation at ER
- Secreted protein by vesicles which then fuse to plasma membrane
Golgi Apparatus
receives proteins and lipids from ER, modifies them and then dispatches them to other destination
endosomes
membrane-bound organelle
material ingested by endocytosis and is transported to early endosomes and sorted
Lysosomes
membrane bound
contains hydrolytic enzymes to digest worn-out proteins and organelles
late endosomes mature into lysosomes
What gives vesicles directionality
directed movement of transport vesicles pulled by motor proteins associated with cytoskeleton
