- Joined
- Jun 9, 2012
- Messages
- 7
- Reaction score
- 0
This is not a question from the USMLE, but wanted to get yall's attention. Where are lysosomal proteins made. RER or free ribosomes or somewhere else?
This is not a question from the USMLE, but wanted to get yall's attention. Where are lysosomal proteins made. RER or free ribosomes or somewhere else?
Medfarmer, although the cis-Golgi would indeed add M6P (via N-acetyl glucosaminyl-1-phosphotransferase) to proteins for trafficking to the lysosome, I would think that RER --> Golgi --> lysosome wouldn't make sense because RER proteins are all destined either for exocytosis or transmembrane-localization (via trans-Golgi). If the proteins originate from within the cell (i.e. not endocytosed), it should be free ribosome --> cis-Golgi --> lysosome, since intrinsically derived proteins are all free ribosome-translated.
Maybe my biochemistry needs some touching up, but any thoughts on that?
I believe the RER actually synthesizes any protein/enzyme that is either destined to be extracellular OR contained and retained in a membrane bound structure (such as the lysosome). It is usually referred to as "extracellular" because it has to pass through a bilipid membrane to get into the lysosome. Free ribosomes make proteins that are initially retained in the cytoplasm or non-membrane bound compartments. (this is coming from faint memories of undergrad cell bio so take it for what it is)
I think you are a little confused. Think of cis and trans as bottom and top respectively not enter and exit (since there is anterograde and retrograde pathways).
first golgi usually works with RER since they are in close proximity to each other while you can have ribosome floating around.
second there are two pathways for the golgi, pathway A and pathway B
Pathway A (anterograde): mRNA --> RER --> proteins --> cis-Golgi --> trans-Golgi --> leave golgi (can be sent to the plasma membrane, lysosome, or excreted out)
Pathway B (retrograde): endosomes --> trans-golgi (can go to ER then back) --> lysosomes or where-ever
On page 79 of FA, 2012 it even says free ribosomes are mainly for cytocytic protein.
Phloston,
RER synthesizes proteins destined for lysosomes (as well as transmembrane proteins and those destined to be exocytosed).
Free ribosomes synthesize proteins destined for peroxisomes, not lysosomes.
I had a very specific question on this in Kaplan Qbank and made sure to annotate accordingly.
I believe the RER actually synthesizes any protein/enzyme that is either destined to be extracellular OR contained and retained in a membrane bound structure (such as the lysosome). It is usually referred to as "extracellular" because it has to pass through a bilipid membrane to get into the lysosome. Free ribosomes make proteins that are initially retained in the cytoplasm or non-membrane bound compartments. (this is coming from faint memories of undergrad cell bio so take it for what it is)
P. 79 of FA doesn't say "mainly for cytocytic protein." It says "cytosolic and organellar" protein.
That also still doesn't address whether free ribosomes send their proteins to the Golgi for epigenetic modification. If they do, cis-Golgi would still be presumptive for receiving those proteins.
Interesting. Thanks for posting that.
/thread 😛
Epigenetics is the modification of DNA into active and inactive states, meaning heritable changes in gene expression. It happens in the nucleus.