delivery of newly synthesised proteins Flashcards
(30 cards)
Where are proteins synthesised in the cell?
On ribosomes either free in the cytosol or bound to the rough ER.
What destinations do proteins from cytosolic ribosomes go to?
Nucleus, mitochondria, peroxisomes, or remain in the cytosol.
What signal does a nuclear protein use for targeting?
NLS – Nuclear Localisation Signal.
What signal is used to send proteins to mitochondria?
MTS – Mitochondrial Targeting Sequence.
What targeting signals are used for peroxisomes?
PTS1 or PTS2 – Peroxisomal Targeting Signals.
Are cytosolic proteins imported into organelles during or after translation?
After translation (post-translational import).
What is the SRP and what does it do?
The Signal Recognition Particle binds signal peptides on nascent proteins, pauses translation, and docks the ribosome to the ER.
What receptor does SRP interact with on the ER membrane?
The SRP receptor.
What channel lets the protein enter the ER lumen or membrane?
Sec61 translocon.
What happens to the signal peptide after ER entry?
It is cleaved by signal peptidase.
What post-translational modifications occur in the ER?
N-linked glycosylation, protein folding by BiP, disulfide bond formation via PDI.
What happens to misfolded proteins in the ER?
They are sent to the ERAD pathway → retrotranslocated → degraded by the proteasome.
What vesicle coats are involved in trafficking?
COPII, COPI, Clathrin.
What is the KDEL signal used for?
Retrieval of ER-resident proteins from the Golgi back to the ER.
What does M6P (mannose-6-phosphate) do?
Directs enzymes to lysosomes.
What are Rab GTPases used for?
Identifying vesicle destinations and recruiting tethering proteins.
How do SNARE proteins enable fusion?
v-SNARE on vesicle pairs with t-SNARE on target membrane.
What disassembles SNARE complexes after fusion?
NSF and α-SNAP.
- NSF- mechanically unwinds SNARE complex
- α-SNAP- guides NSF to SNARE complex
α-SNAP also plays a role in monitering the zipping process in the formation of SNARE complex
Why is proper protein trafficking important?
It ensures proteins function in the correct location and prevents disease.
What should go in the Introduction of an essay on protein delivery?
Define protein targeting and trafficking, explain its importance, mention synthesis locations.
What are the key points in the Main Body – Cytosolic Ribosomes?
Synthesis of proteins for nucleus, mitochondria, peroxisomes; use of targeting signals; post-translational import.
What are the key points in the Main Body – ER-Bound Ribosomes?
SRP recognises signal peptide, docks to ER, translocation through Sec61.
What should be covered under Post-Translational Modifications?
Glycosylation, protein folding by BiP, disulfide bond formation, quality control via ERAD.
What are the key Vesicle Trafficking pathways to include?
COPII, COPI, Clathrin; sorting tags KDEL, M6P.
