Protein Trafficking

Question 1

Different proteins have different ______ after synthesis

Answer 1

destinations

Question 2

what are the membrane bound compartments

Answer 2

ER, nucleus, lysosomes, mitochondria, cell membrane,

Question 3

____proteins contain signals that determine their ultimate destination

Answer 3

Nascent

Question 4

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

Answer 4

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

Question 5

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

Answer 5

free;
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

Question 6

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 ___ ____

Answer 6

rough ER. N-terminal. signal peptidase

Question 7

How does protein trafficing through the RER work?

Answer 7

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)

Question 8

how do synthesis of all proteins begin by

Answer 8

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

Question 9

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

Answer 9

signal recognition particle (SRP)

Question 10

How does SRP receptor direct peptide to translocation complex?

Answer 10

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

Question 11

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 _____

Answer 11

signal peptidase. Chaperones. Irreversible.

Question 12

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

Answer 12

ER; pentasaccharide core

Question 13

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

Answer 13

dolichol; carrier; isoprenoid

Question 14

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

Answer 14

ER membrane

Question 15

Where are the sugars located?

Answer 15

First 7 sugars on outside, next 7 on inside.

Question 16

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

Answer 16

oligosaccharide. Asn. pyrophosphate

Question 17

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

Answer 17

cytosolic; lumen

Question 18

How is dolichol phosphate regenerated

Answer 18

phosphatase

Question 19

what are drugs that affect addition of sugars

Answer 19

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

Question 20

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

Answer 20

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).

Question 21

Membrane ___ of membranes is central to function

Answer 21

assymetry

Question 22

In order to target lysosomes what needs to be attached?

Answer 22

mannose 6 -phosphate

Question 23

How does phosphate get transferred to mannose?

Answer 23

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.

Question 24

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

Answer 24

phosphotransferase; phosphodiesterase

Question 25

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

Answer 25

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)

Question 26

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

Answer 26

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

Question 27

What is receptor mediated endocytosis impt for

Answer 27

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.

Question 28

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.

Answer 28

coated pits; endosome

Question 29

Endosomes are acidified by ________ in membranes.

Answer 29

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

Question 30

What is transferrin

Answer 30

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.

Question 31

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

Answer 31

Semliki; Diptheria

Question 32

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

Answer 32

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

argenine, His, Ile, Leu