Question

1. Where is the ER targeting sequence located in the polypeptide chain (N-terminal, interior, or C-terminal) 2. Name 4 organelles that require organelle specific targeting sequences in polypeptide 3. Name 3 final locations for proteins with ER signal sequence 4. Satranslational translocation: (a) Name the protein that the signal sequence binds to (b) Name the protein SRP binds to 5. State the function of signal peptidase 6. Name a membrane protein that is not a single pass membrane protein 7. (a) Name the 14 residue aligosachbaride that is initially added to proteins, and (b) name the molecular responsible for the addition 8. (a)Name the enzyme involved in disulphide bond formation, and (b) the protein that oxidizes it 9. Name the transcription factor involved in the unfolded protein response 10. Name the targeting sequence for proteins with final cytoplasmic location

Answer 1

1. ER targeting sequence is located in the N terminal of the polypeptide chain.It contains hydrophobic residues and some amino acids.
2. Endoplasmic reticulum, Choloroplast(in plants), peroxisomes and mitochondria are the organelles that require organelle specific targeting sequences in polypeptide. All require specific targetting sequence to direct protein into organelles.
3. RER involved in protein synthesis , The protein then moves to the ER lumen ( signal sequence removed), for packaging purpose it moves to the cis face of golgi apparatus and are released as vesicles through trans face. These membrane bound vesicular structures formed are called lysosomes which contain enzymes capable of digesting proteins.
4. a) signal sequence emerging from ribosome binds to SRP ( have 6 polypeptide and a small cytoplasmic RNA) thus helping in translation b) SRP binds to the SRP receptor protein ( docking protein)