Secretory Pathway Flashcards
What are the two pathways for protein sorting?
Targeted to an organelle or to be secreted
What is the first event in the secretory pathway?
Entry into the endoplasmic reticulum (ER)
What are the intended learning outcomes of the session?
Understand how newly synthesised proteins are targeted to cellular organelles and the secretory pathway, and appreciate critical modifications during secretion.
What are the three mechanisms by which organelles import proteins?
- Directly from cytosol
- Via the ER
- Through nuclear pores
What is an uptake-targeting signal?
Short conserved sequences that direct proteins to their target organelle
What is the nuclear localization signal (NLS)?
A sequence that directs proteins into the nucleus, for example, Pro-Pro-Lys-Lys-Lys-Arg-Lys-Val
True or False: Most mitochondrial proteins are synthesized within the mitochondria.
False
What is the role of chaperone proteins in mitochondrial protein import?
Assist in protein unfolding prior to import
What is the peroxisome targeting sequence for catalase?
SKL (Ser-Lys-Leu) sequence at C-terminus
What type of proteins do peroxisomes import?
Fully folded/assembled proteins
What is the process of cisternal progression in the secretory pathway?
Proteins within vesicles do not re-enter the cytoplasm
What initiates the interaction of signal sequences with the ER membrane?
Signal recognition particle (SRP) binds to the signal peptide
What are the five principal modifications that occur in the rough ER?
- Formation of disulfide bonds
- Proper folding
- Specific proteolytic cleavages
- Signal peptide removal
- Proprotein processing
What is the role of protein disulfide isomerase (PDI)?
Assists in the formation of correct disulfide bonds
What is glycosylation?
The addition of carbohydrate moieties to proteins
What are the two types of glycosylation?
- N-linked (asn-x-ser/thr)
- O-linked (ser/thr)
Fill in the blank: Proteins are synthesized on ribosomes in the _______.
cytosol
What is the function of the SRP receptor in the ER?
Binds to the SRP-bound complex to facilitate protein translocation
What happens to the signal peptide during translocation into the ER?
It is cleaved by signal peptidase
What is the consequence of proper glycosylation for some proteins?
Enhances stability and may be necessary for folding
What is the role of the GPI anchor?
Transfers some proteins to the ER membrane
What type of environment in the ER lumen aids in disulfide bond formation?
Redox environment
What is the role of ATP in mitochondrial protein import?
Required for the active process of import
How are large molecules prevented from passing through nuclear pores?
Water-filled passage with disoriented protein tangles
What is the function of catalase in peroxisomes?
Converts H2O2 into H2O
