AAMC official guide bio protein question

[Whiteshoes]

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This is referring to the 1st passage in bio section question 2.

how do you know if proteins are synthesized in the cytosol or the Rough ER?
because I've read the proteins are made in the rough ER but I also know that Mrna enter the cytosol from the nucleus and bind to ribosomes in the cytosol.

Here's the question on page 211

Which of the following best traces the cellular location of GBA immediately after its release from the ribosomes to its arrival at its functional location?

B. Rough ER -> Golgi apparatus -> lysosome

or

D. Cytosol -> lysosome

 

[Phlame217]

The cellular mechanics is the mRNA enters the cytosol from the nucleus where one subunit of the ribosome binds triggering the opposite to bind. The mRNA itself possesses a localization signal that tells it to bind the rER and then upon binding allows the translation to proceed. The peptide is produced and enters the rER where it is checked for errors and then sent to the Golgi where it may be modified and it obtains a localization signal for where in the cell it where go and is then packaged and sent off to that area.

So yes, B is the best answer.

 

[Whiteshoes]

The cellular mechanics is the mRNA enters the cytosol from the nucleus where one subunit of the ribosome binds triggering the opposite to bind. The mRNA itself possesses a localization signal that tells it to bind the rER and then upon binding allows the translation to proceed. The peptide is produced and enters the rER where it is checked for errors and then sent to the Golgi where it may be modified and it obtains a localization signal for where in the cell it where go and is then packaged and sent off to that area.

So yes, B is the best answer.

Thank you!

 

[MD Odyssey]

The cellular mechanics is the mRNA enters the cytosol from the nucleus where one subunit of the ribosome binds triggering the opposite to bind. The mRNA itself possesses a localization signal that tells it to bind the rER and then upon binding allows the translation to proceed. The peptide is produced and enters the rER where it is checked for errors and then sent to the Golgi where it may be modified and it obtains a localization signal for where in the cell it where go and is then packaged and sent off to that area.

So yes, B is the best answer.

I'm a little bit confused. Doesn't this answer presuppose that the protein being produced is marked for secretion from the cell? Or does the question state someplace that GBA is secreted from the cell or gets packaged into a vesicle?

Or, are you arguing that all proteins get processed through the rough ER?

 

[Phlame217]

Theres exceptions to every rule, but generally, all proteins are processed by the rER. For the MCAT, you shouldn't go wrong with that idea.

The distractor of the Cytoplasm -> Lysosome would be the pathway for the protein to be broken down to amino acids and recycled. The key in this question is it mentions the synthesis of the protein.

 

[MD Odyssey]

Theres exceptions to every rule, but generally, all proteins are processed by the rER. For the MCAT, you shouldn't go wrong with that idea.

The distractor of the Cytoplasm -> Lysosome would be the pathway for the protein to be broken down to amino acids and recycled. The key in this question is it mentions the synthesis of the protein.

So, cytosolic proteins are still synthesized on the rough ER and get sent through the Golgi?

 

[geeyouknit]

Theres exceptions to every rule, but generally, all proteins are processed by the rER. For the MCAT, you shouldn't go wrong with that idea.

The distractor of the Cytoplasm -> Lysosome would be the pathway for the protein to be broken down to amino acids and recycled. The key in this question is it mentions the synthesis of the protein.

Uh, the bolded answer has "lysosome" in it too.
The reason lysosome is in all the pathways is that GBA is an enzyme that is stored in lysosomes to break complex sugars down.

According to EK, all translation starts off in ribosomes in the cytoplasm. If the polypeptide in the process of being created from the ribosome has a special molecule called signal peptide, then the ribosome attaches to the rER and the protein stays in the ER-Golgi-Lysosome-membrane network. If not, the protein is made in cytoplasmic ribosome and stays in the cytoplasm.