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Flashcards in Protein Trafficking Deck (32)
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Different proteins have different ______ after synthesis



what are the membrane bound compartments

ER, nucleus, lysosomes, mitochondria, cell membrane,


____proteins contain signals that determine their ultimate destination



whats the difference bet. free ribosome and one thats found on the rough ER

nothing! all ribosomes start out as free ribosomes. Location is det by protein being synthesized and protein trafficking.


Nuclear, peroxisomal and mitochondrial proteins are made by ____ ribsomes in cytoplasm. What are the signal seq used by these proteins?

Nucleus: internal nuclear localization seq's.
Peroxisome: C terminal seq SKF (serine, lys, phe)
Mitochondrial matrix: N terminal seq rich in + charged aa (Lys, Arg) & serine and thr


Secretory, lysosomal & integral membrane proteins are made in the ______A __ ___ signal seq on the nascent polypeptide directs the ribosome to attach to the ER. The signal seq is removed from the secreted protein by cleavage by ___ ____

rough ER. N-terminal. signal peptidase


How does protein trafficing through the RER work?

N terminal sec. peptide signal seq have common features:
1. range in length from 13-26 residues
2. amino terminal part of signal contains at least 1 + charged residue.
3. A highly hydrophobic stretch of usually 10-15 residues forms the center of the signal.
4. The residue on the amino terminal side of the signal peptidase cleavage site usually has a small, neutral side chain (alanine)


how do synthesis of all proteins begin by

free ribosomes binding to mRNA and commencing synthesis of N- terminal region of polypeptide


__ ___ ___ is an RNA protein complex that recognizes & binds to signal seq's. Binding of this temporarily arrests translation by ribosome

signal recognition particle (SRP)


How does SRP receptor direct peptide to translocation complex?

1. Bound SRP directs the ribosome with incomplete peptide to a specific SRP receptor on the cystolic face of the ER.
2. The SRP receptor delivers the signal peptide (& ribosome) to the peptide translocation complex on the cystolic face of the ER.
3. SRP binding to receptor releases GDP, GTP binds in its place. SRP is released from ribosome & signal peptide threds through peptide translocation complex.
4. GTP is hydrolyzed and SRP is rel from receptor


Once signal peptide and some foll. peptide is in the lumen, __ ___ cleaves signal peptide off growing chain. ATP driven heat shock proteins serve as ____to assist correct peptide chain folding. Entry into ER is _____

signal peptidase. Chaperones. Irreversible.


Glycoproteins acquire core sugars in ____. N linked to asparagine. O linked to serine and threonine. N linked oligosaccharides have a common ____ ___ derived by trimming a 14 residue core oligosaccharide added to specific Asn residues

ER; pentasaccharide core


N linked glycoproteins use ______ phosphate as a ______. Dolichol phosphate is an _____ derivative, a lipid, and is localized to membranes

dolichol; carrier; isoprenoid


Half of the core oligosaccharides are synthesized on cytosolic side of ER via nucleotide activated (UDP or GDP) sugar precursors. Incomplete core dolichol pyrophosphate is translocated across ______ _____ into lumen

ER membrane


Where are the sugars located?

First 7 sugars on outside, next 7 on inside.


Dolichol phosphate activated sugars are used to complete core ____. Oligosaccharide transferred to specific ___ residues in protein, releasing dolichol ____.

oligosaccharide. Asn. pyrophosphate


Nucleotide activated precursors are on ____ side. Dolichol phosphate activated precursors on ___ side

cytosolic; lumen


How is dolichol phosphate regenerated



what are drugs that affect addition of sugars

1. Tunicamycin: blocks the first step in oligosaccharide synthesis.
2. Bacitracin: Blocks phosphatase that recycles dolichol phosphate.


Transport vesicles play an important role in transporting proteins. Where do they transport them?

When ER buds off it bec smooth ER and is going to transport proteins to cis Golgi which is side closest to ER which get further modified and get sorted to trans side (closest to cell membrane).


Membrane ___ of membranes is central to function



In order to target lysosomes what needs to be attached?

mannose 6 -phosphate


How does phosphate get transferred to mannose?

Take UDP sugar and add it on. Comes off as UMP which leaves off a phosphate. Take off N acetyl glucosamine and leave phosphate to transfer to mannose.


Phospho N acetyl glucosamine group is added to a mannose by what enzyme? What enzyme removes N-ac-Gln leaving mannose 6-phosphate in core oligosaccharide

phosphotransferase; phosphodiesterase


What is the default pathway (out of Golgi) of vesicles being target to lysosomes? What is the disease associated with this?

Secretion! Get secreted out of cell. We cant break things down properly in lysozome and we get really sick:
I cell disease: Deficient in the phosphotransferase (Puts UDP on mannose)


What is a return signal for proteins to go back to the ER?

The carboxy terminal seq KDEL ( Lys, Asp, Glu, Leu) signals them to return back from Golgi to ER.


What is receptor mediated endocytosis impt for

1. means of delivering essential metabolites
2. modulates response to many protein hormones and growth factors.
3. extracellular proteins targeted for destruction taken up & delivered to lysosomes.


Many receptors loc in specialized regions of plasma membrane called __ ___. Cytosolic side of indentation has thick coat of clathrin protein. Endocytosis begins with invagination of coated pit triggered by receptor ligand binding. Clathrin forms lattice around coated pit, excising it from membrane and forming coated vesicle. Coated vesicle rapidly loses clathrin shell and fuses with an ____which are usually large & have acidic lumens.

coated pits; endosome


Endosomes are acidified by ________ in membranes.

ATP driven proton pumps. Acidic env leads to dissociation of protein receptor complexes.


What is transferrin

Transports iron from sites of absorption & storage to sites of utilization. Transferrin binds to receptor in coated pits. (Needs iron to bind). Can be fused with endosome where acidification causes release of iron and transferrin from receptor. Iron gets transferred to ferritin and receptor is recycled.


certain viruses and toxins can enter cells through endocytic pathways. ____ virus which is related to yellow fever enters susceptibl cells by bindig to receptors in coated pits and is endocytosed. pH change in endosome triggers release of viral nucleocapsid from membrane. ____ toxin enters cells by binding to growth factor receptor and is internalized by endocytosis

Semliki; Diptheria


Protein get degraded by ____tags via 28s proteosome. Signal for ubiquinylation and therefore protein stability is ___ ___ __What are the stable proteins?
what about unstable?

ubiquitation; N- terminal amino acid.
Glycine, alanine, cysteine methionie

argenine, His, Ile, Leu