Pintar - Vessicle trafficing

Question 1

Zellweger Syndrome

Answer 1

There are many enzymes that are sent to the internal side of the peroxisome. In this syndrome, some enzymes can’t get into the peroxisome and are left in the cytoplasm and are degraded. There is a receptor that recognizes the peroxisomal signal sequence which is screwed up and can’t recognize the peroxisomal signal sequence.

Question 2

What proteins go through the RER/Golgi pathway and which don’t?

Answer 2

Do: lysosomes, endosomes, cell surface, secretory vesicles.

Don’t: Nucleus, mito, peroxisomes, cytosol, plastids

Question 3

Signal Recognition Particle (SRP)

Answer 3

Recognizes specific and distinct signal on the N-terminal side of proteins (first side that is synthesized). If it is bound for the secretory pathway then the SRP will bind to it, halt translation, and relocate it to a SRP receptor on the ER membrane. Translation will then continue into a channel into the ER membrane. Then a few other things happen:

1) The signal sequence is removed
2) hydroxylation of Lys, Pro
3) disulfide bonds form
4) chaperones come to aid in folding - if bad folding then proteasome
5) glycosylation of Lys and Pro usually
- You can tell how far a protein is in packaging by looking at the extent of glycosylation on the proteins.

Question 4

3 types of coats for vesicles

Answer 4

Clathrin - endocytosis and transport steps to and from the TGN. Adaptin actually binds to the receptor as well as the clathrin. So, adaptin is the intermediary between clathrin and the receptor.
Coatamer 1 (COP1) - Forward traffic and reverse traffic through the Golgi (if misrouted, KDEL sequence)
Coatamer 2 (COP2) - Exit from the ER

Question 5

COP II mechanism

Answer 5

When the Sar-1 is converted to a GTP bound state by a GEF, there is a conformational change which exposes the lipid tail on the protein to be exposed and as a consequence it can recognize the donor membrane. Once this happens, the other coat proteins can bind. COP I is the same but has ARF instead of Sar-1

Question 6

Snares

Answer 6

Acts as a lock and key interaction where there has to be an exact match between vesicles to different compartments (Rab help mediate accuracy). Botulinum and tetenus toxin will affect the transmission of neurotransmitters which act in a vesicular mechanism. V and T snares (T for acceptor membrane and V for donor membrane)

Question 7

What modifications happen to enzymes that are targeted for the lysosome?

Answer 7

There is a phosphate added to a mannose sugar group. Those then go through the golgi and meet up with a mannose-6-phosphate receptor on the TGN. They are then packaged into clathrin vesicles and delivered to a late endosome. The acidic pH will cause the enzymes to be released from the receptor. The receptor then buds off and is recycled back.
If there is a mutation in the phosphotransferase then the lysosomal enzymes will not be recognized by the TGN and they will not be sent to lysosomes and instead all of the things that are supposed to be degraded by the lysosome are all secreted. Additionally, the enzymes that are supposed to go to the lysosome are also secreted.

Question 8

Legionairre’s Disease

Answer 8

Hijack normal trafficking patterns of the cell to allow bacteria to enter the cell and block delivery of things to the lysosome.

Question 9

3 things that can happen from an early endosome

Answer 9

1) recycling
2) constitutive pathway
3) transcytosis - happens for fetuses and mothers in delivering antibodies to the baby.

Question 10

LDL cholesterol

Answer 10

Basically LDL binds to the LDL receptor. Then it is endocytosed and coated with clathrin. It is then decoated. It goes to the early endosome where it is acidic, causing the receptors to be released and are budded off and recycled back to the membrane. The late endosome then turns into a lysosome and degrades the back cholesterol (it saves the good cholesterol first). One way to regulate the response to extracellular ligands is by not recycling the receptors and just degrading them.

Question 11

Cholesterol mutation

Answer 11

mutation in the receptor tail (the part that binds to adaptin). It can bind to LDL cholesterol normally but the adaptin never binds to the receptor and therefore the material is never internalized. Therefore there is very high cholesterol levels.

Question 12

Post translational modification sending things to the right places

Answer 12

There is a AA sequence that is put onto the protein that tell it where to go. The binding of the signal sequence on the end is recognized by what is called an “importan”. The whole complex then winds its way through the nuclear pore into the nucleus. Then the binding has to be reversed. This is done by what is called RanGTP, which has a high concentration in the nucleus. This is done by having a GEF only in the nucleus. RanGTP binds to the complex and causes a conformational change that releases the protein and the complex. GAPs are then used to inactive the Ran.