ER & Secretory Pathway Flashcards
Describe the structure of the endoplasmic reticulum
- single membrane continuous network of tubular and flat vesicular structures
- space inside filled with fluid different to cytosol
What are the 2 types of ER?
- Rough ER: ribosome’s attached for the translation nd folding of proteins
- Smooth ER: synthesis of lipids and detox of drugs
What is the function of the RER?
protein synthesis, glycosylation, folding and assembling of multi protein complexes
What is the function of the SER?
lipid synthesis, Ca2+ sequestration, detox by cytochrome p450 enzymes
What are resident proteins?
proteins that are manufactured in the ER and stay in the ER
How to resident proteins stay in the ER?
they have a retention signal which allows them to not be transported out
What does BiP do?
identifies proteins that have been made incorrectly and prevents them from going to their final destinations
What is Ca2+ sequestration?
storage of Ca2+ ions inside the lumen of the SER
What doe p450 enzymes do?
- detoxification and transforms the inactive form of the drug to the active form
- occurs in ER of liver
How are secreted protein different to resident proteins?
they have a sequence at 5’ end which is rich in hydrophobic aa
What are the difference between free and bound ribosomes?
- free ribosomes are in the cytosol and translate soluble proteins for the release into the cytoplasm (nucleus, mitochondria, peroxisomes, chloroplasts_
- bound ribosomes translate proteins which are secreted or incorporates into membrane of lysosomes, secretory vesicles and endosomes
What is protein translocation?
process by which proteins move between cellular compartments
What are the steps for co-translational protein targeting to the ER?
- translation begins at a ribosome that is free in the nucleus
- when the signal sequence emerges from the ribosome, the signal recognition particle (SRP) interacts with it and guides it to an SRP receptor in the membrane of the ER.
- the SRP helps dock the ribosome onto a translocon so the ribosome becomes part of the ER.
- once the ribosome is attached translation continues and the PP chain passes into the ER while the signal sequence remains bound to the channel.
What does the signal sequence determine?
whether the ribosome that is translated is free or bound
How does insulin get modified?
- when insulin is secreted, it is called preproinsulin and has a signal sequence that leads it to a translocon
- signal sequence gets cleaved off and after it is called proinsulin
