Lecture 9 Flashcards
What does the endomembrane system consist of?
ER, Golgi complex, lysosomes and vacuoles
what are the 3 steps of membrane-bound transport for vesicles?
- bud from a donor membrane
- Movement via motor proteins on microtubules and microfilaments to the cytoskeleton
- fuse with the membrane of the acceptor compartment
What are the 3 pathways of the Endomembrane System?
Biosynthetic
Secretory
Endocytic
What is the Biosynthetic pathway?
Proteins made in ER, modified at Golgi complex, transported to various destinations
What is the Secretory pathway?
Proteins made in ER then discharged from cell
What is the Endocytic pathway?
materials move from outer surface of the cell to compartments (endosomes and lysosomes)
What are the 2 secretion modes?
Constitutive and regulated
What is constitutive secretion mode?
materials are transported in secretory vesicles and discharged in a continual manner
what is regulated secretion?
materials are stored in vesicles and discharged as a response to stimulus
what 3 cells does regulated secretion occur in?
Endocrine, pancreatic and nerve cells
Where are the secreted materials in regulated secretion stored in?
Secretory granules
how are secreted materials routed to the proper destination?
through sorting signals encoded in amino acid sequences
how does autoradiography work?
visualization of biochemical processes through radioactively labeling molecules
what does fluorescent proteins visualize?
production and movement of viral proteins
what does subcellular fractions visualize?
isolation of the smooth and rough ER to determine lipid and protein composition
what insights were gained from using Cell-Free systems?
the study of proteins that bind to the membrane to initiate vesicle formation
proteins responsible for transport material selection
proteins responsible for severing the vesicle from the donor membrane
what insights where gained from mutant phenotypes?
reveals the proteins that function in secretion
What is the function of the endoplasmic reticulum?
Network of membranes that penetrates much of the cytoplasm
separates Lumen from the Cytosol
Contrast the Rough and Smooth ER
Rough: Ribosomes bound to surface, flattened sacs, continuous with the outer membrane
Smooth: Lacks ribosomes, membrane is highly curved, continuous with the Rough ER
what are the functions of the Smooth ER?
Hormone synthesis in endocrine cells
detoxification of organic compounds in liver (cytochrome P450)
Calcium ion sequestration and regulated release
what are the functions of the rough ER?
Near basal surface (facing blood supply)
starting point for pathway of secretory proteins
1/3 of protein synthesis
what determines the site of protein synthesis?
the sequence of amino acids in the N-terminal portion
where does the signal sequence of secretory proteins direct the polypeptide and ribosome to?
the ER membrane
what does the polypeptide move through in the ER as it’s being synthesized?
the cisternal space which is lined with proteins
where does co-translation translocation deposit the protein?
Into the ER Lumen
what recognizes the signal sequences?
the signal recognition particles (SRP)
What are the steps to produce secretory, lysosomal or vacuolar proteins?
Signal recognition particle (SRP) binds to polypeptide and ribosome to halt synthesis
complex is recruited to the ER membrane through the SRP & SRP receptor on ER membrane
Ribosome is handed of to a protein channel in the ER membrane (called a Translocon)
Polypeptide is then injected into the ER Lumen through the Translocon
