Follow a Protein to the ER
Many proteins enter the secretory pathway while they are still being translated.
Living-system questions are solved by matching a structure or organism to its function, process and stated condition.
Ribosome targeting to ER
Translation begins on a free cytosolic ribosome. Signal recognition particle (SRP) binds the emerging signal sequence and targets the ribosome to an ER translocon. Translation resumes with the growing chain entering the ER, so translocation is co-translational; a fully folded protein does not simply pass through the membrane.
Follow secretory proteins with pulse-chase
New secretory proteins enter the rough ER during synthesis, move to the Golgi for processing and sorting, and later collect in secretory granules. A short pulse-chase therefore shows label peaking in ER first, Golgi next, and granules later.
OlympIQ exam lens
- ✓SRP recognises the emerging signal sequence.
- ✓Ribosome docks at ER and translation continues during translocation.
- ✓Entry is generally co-translational, before full folding.
The ribosome is not the signal-sequence receptor; SRP is.
Ready to try the pattern?
100% coverage across the 2 linked questions.
Practise 2 linked questions