SM13 Flashcards
(14 cards)
Which side of Golgi is closest to er?
cis
What is the signal hypothesis for protein transport into the ER?
Proteins destined for the ER are synthesized as precursor proteins with an amino terminal extension called the signal sequence that assoc with SRP (signal recognition particle) which stops translation. This will assoc with SRP receptor in the ER membrane. It transfers the signal seq from SRP to the channel and the SRP is displaced and rescued. Signal seq remains assoc with the channel until the protein is transferred. Dissociation of the SRP and the SRP receptor from the ribosome allows translation to resume with assoc chaperones like BIP (an ATP-dependent chaperone). fter ~150 amino acids have entered the lumen, a protease called signal peptidase cuts off the signal peptide, which is rapidly degraded.
Describe N-linked glycosylation.
Addition of 14 sugar oligosaccaride which containes glucose, mannose and N-acetyglycosamine. Linked to asparagine (N). Sugar is made on cytoplasmic side of ER and then flipped into lumen when it is made. It is synthesized, linked to dolicol which will anchor the sugar in the membrane. Then oligosaccaride protein transferase will transfer the sugar to the growing polypep. All proteins entering ER get sugar link
Which type of proteins will exchange their carboxyl terminal transmembrane segment for an oligosaccharide accord to phosphatidylinositol, called the GPI anchor?
receptor and cell-cell recognition proteins on extracellular side of the cell.
_____ is a calcium binding protein that monitors the folding of glycoproteins.
Calnexin. The unfolded protein with oligosaccharide chain will get trimmed. Calnexin recognizes the partially modified oligosaccharide, helps the protein fold and then it releases it the protein, which will interact with glucosidase which will trim more and then the protein will interact with gluocssyl transferase which will add more sugar using UDP-glucose as donor
The ER lumen is an oxidizing environment similar to to the outside of the cell. This allows for the formation of which type of bonds.
Disulfide bonds catalyzed by protein disulfide isomerases (PDIs).
Lumen of vesicles in cells are equiv to env in _______
the outside of the cell
cargo react with certain adaptors in membrane which will aggregate to bend membranes and form vesicles. Give examples of two.
1) Clathrin - for Golgi to lysosome and plasma membrane and endocytosis.
2) Adaptins - capture specific membrane proteins.
Membranes are negatively charge and repel. How do we get two membranes to fuse?
In the vesicle, Rab will bind to tethering protein on the target membrane. V-Snare on vessicle will interact with t-Snare on the target membrane. These will associate and bring vessicle and target membrane in close proximity and help aid their fusion
Cop is similar to clathrin but is involved in which kind of transport.
Cop II is involved in ER to Golgi
Cop I is involved in Golgi to Golgi and Golgi to ER
Resident ER proteins get caught up in vesicle to Golgi but need to go back to ER. How?
They have KDEL seq in them that binds KDEL receptor that is taken up in Cop I coats and delivered in vesicle to ER.
How to we transport lysosomal hydrolyses to the lysosome from Golgi?
All hydrolyses have M6P, which is recognized by M6P receptor and form clathrin coated vesicle. After vesicle formed clathrin removed and those v-snares and t-snares target it to lysosome where hydrolyses are released because of acidic env of the lysosome. The Phosphate is removed form M6P and active lysosomal hydrolyses is modified by branched sugars containing mannose to form early endoscope. Receptors targeted back to trans Gold by retromer coat (similar to clathrin)
Endocytic pinocytosis is important in which processes?
exchange of maternal antibodies across placenta; viral infection and prion disease through caveolae
What are the two types of exocytosis?
1) constitutive - unregulated - formation of vesicle from trans-golgi, uncaring and fusing with PM to grow the PM, release of cargo etc.
2) regulated secretion - these remain in the cytoplasm until signal from cell tells them to fuse with PM (this is what happens in neurotransmission). Signals include hormones/neurotransmitters.
