Proinsulin cleavage

[Miracoli]

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Cleavage of proinsulin to insulin occurs in the :
a) cytosol
b) RER
c) Golgi
d) Secretory vesicle
e) Lysosome

 

[seminoma]

D

 

[Miracoli]

Robbins says it is Golgi

 

[dfib slim]

Robbins says it is Golgi

As does Costanzo. Cleavage occurs in the golgi immediately prior to packaging. Then both insulin and c peptide is secreted together.

 

[seminoma]

Robbins says it is Golgi

As does Costanzo. Cleavage occurs in the golgi immediately prior to packaging. Then both insulin and c peptide is secreted together.

As does Lippincott biochem. My mistake!

 

[CodeRedDew]

Definitely thought it was secretory granules as well, good to know! Also, you guys may want to edit what's in FA in the beginning of the Endocrine physiology section since it's not really clear (below).

 

[Miracoli]

So sources that say Golgi: UW, Robbins, lipincot biochem, costanzo physio, guyton physio
secretory vesicle:UW, Berne-levy physio, Marks biochem, Uptodate.com
Who do you trust?

 

[seminoma]

So sources that say Golgi: UW, Robbins, lipincot biochem, costanzo physio, guyton physio
secretory vesicle:UW, Berne-levy physio, Marks biochem, Uptodate.com
Who do you trust?

UW says both?

 

[bigdogrob4284]

I just had an Rx question on this. In the explanation, it says that proinsulin is packaged into vesicles and then transported to the golgi, where it is cleaved to form the active hormone insulin.

 

[Transposony]

If you know the mechanism of how protein synthesis and packaging works then there will be no confusion.
Proinsulin is packaged in the Golgi apparatus with protease and released together as a secretory vesicle. It cannot be other way around since Golgi IS the packaging center.
Once the appropriate signal is received, protease then splits the proinsulin into C peptide and the active insulin. The secretory vesicle fuses with the membrane and both are released.

 

[seminoma]

If you know the mechanism of how protein synthesis and packaging works then there will be no confusion.
Proinsulin is packaged in the Golgi apparatus with protease and released together as a secretory vesicle. It cannot be other way around since Golgi IS the packaging center.
Once the appropriate signal is received, protease then splits the proinsulin into C peptide and the active insulin. The secretory vesicle fuses with the membrane and both are released.

But why can't cleavage occur in the golgi vesicle before being released (like DA -> NE in neuronal vesicles)?

 

[CodeRedDew]

Things like this make me wonder why this type of stuff is important to clinical medicine lol - if 3/4 specialized resources are conflicted on EXACTLY where, then why does it matter!?

 

[Transposony]

But why can't cleavage occur in the golgi vesicle before being released (like DA -> NE in neuronal vesicles)?

Apples and Oranges.
Insulin is a secreted protein and synthesized as an inactive preprohormone as compared to DA/NE etc which are synthesized as active amines.
The "pre" part is a signal sequence which is cleaved off in ER.
The "pro" part is cleaved off in the vesicle where the proinsulin is "packaged" by Golgi with protease.

 

[Transposony]

Things like this make me wonder why this type of stuff is important to clinical medicine lol - if 3/4 specialized resources are conflicted on EXACTLY where, then why does it matter!?

That's exactly the reason why they can't directly ask this on the test except to test the concept of protein synthesis and trafficking.