Endomembrane System Flashcards
O-linked Glycosylation
binding of sugars to -OH of serine, threonine and in collagen to hydroxylysine
What signal directs proteins into lysosomes?
Mannose-6-phosphate
Pinocytosis
the ingestion of liquid into a cell by the budding of small vesicles from the cell membrane
Caveolae
a special type of lipid raft, are small (50–100 nanometer) invaginations of the plasma membrane in many vertebrate cell types, especially in endothelial cells and adipocytes
Transcytosis
transcellular transport in which various macromolecules are transported across the interior of a cell. Macromolecules are captured in vesicles on one side of the cell, drawn across the cell, and ejected on the other side
What are the functions of the Endoplasmic Reticulum?
transmembrane protein and lipid synthesis, lysosomal protein synthesis, lipid synthesis for organelle synthesis
What is the purpose of the Smooth ER?
lipid synthesis, detoxify lipid soluble drugs, sequester calcium, and repair proteins
How are ribosomal complexes directed to the ER?
N-terminal signal peptides
What is a SRP?
Signal Recognition Particle that binds to the signal sequence of polypeptide and then binds to its receptor in the rough ER
Translocon
a complex of proteins associated with the translocation of polypeptides across membranes.
Which sub-unit of the Ribosome binds to the protein translocator in the ER membrane?
Large Ribosomal subunit
How is the Nascent peptide inserted into the translocon?
GTP binding and hydrolysis
What are the steps leading to insertion of protein into translocon?
GDP-SRP binds to signal sequence of polypeptide ribosome complex, GDP exchanged for GTP, complex binds to SRP receptor on the membrane of ER, hydrolysis of GTP results in release of the SRP-receptor and insertion of the nascent peptide into the translocon and release of the SRP
Sector 61 complex
an endoplasmic reticulum (ER) membrane protein translocator
Post-translational Translocation
Translocation happens after the polypeptide has been translated
Co-Translational Translocation
Translocation happens while the polypeptide is being translated
What do Stop transfer signal do?
Anchor the protein in the membrane
What are the steps to the anchoring of protein in the membrane?
Start signal on the protein binds the translocon. The peptide moves through the translocon until it reaches the stop transfer signal which binds to the translocon. These 2 hydrophobic regions are moved from the translocon to the membrane and stay anchored
N-linked Glycosylation
most common form of glycosylation where sugars are attached to sparagine residues
How do complex sugars end up in the ER?
Sugars are added to dolichol phosphate (which is in the ER membrane) in the cytosol using oligosaccharyl transferase. the sugars are then flipped across the membrane into the ER lumen
What happens in the Gogli?
the modified glycosylated proteins are trim and added with additional sugar
How are misfolded proteins destroyed in the cytosol?
they are tag with ubiquitin and chopped up in the proteasome
GPI
glycoslyphosphatidyl inositol used as a lipid anchor to attach proteins to the membrane
Where are most membrane lipids synthesized?
ER
How are lipids moved within the cell?
phospholipid exchange protein
