Just Joshin

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In the Bio book, one of the questions asks:

Translation in a eukaryotic cell is associated with each of the following organelles or locations except:

(1) mitochondrial matrix
(2) cytosol
(3) nucleus
(4) the rough ER

The answer is nucleus, but I thought rRNA needed the nucleolus which is part of the nucleus so I don't get it.
 

neutropos

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True, it needs the nucleolus, but it needs it for transcription, not translation. Proteins that are part of the ribosome are brought into the nucleolus which will complex with rRNA to form the subunits of the ribosomes.
 

Just Joshin

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I'm sorry I don't understand. I haven't taken Bio I in four years so I've forgotten all this stuff. It says that rRNA is actively involved in translation so where does translation take place? In the cytosol? Does transcription take place in the nucleolus then?
 

neutropos

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No worries dude.

The rRNA itself is transcribed in the nucleolus. It complexes with proteins that were recruited to the nucleolus to form the subunits of ribosomes. These subunits leave the nucleus and enter the cytosol. In the cytosol, the subunits will come together to translate mRNA into protein.
 
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Just Joshin

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No worries dude.

The rRNA itself is transcribed in the nucleolus. It complexes with proteins that were recruited to the nucleolus to form the subunits of ribosomes. These subunits leave the nucleus and enter the cytosol. In the cytosol, the subunits will come together to translate mRNA into protein.

Hey thanks! That makes a lot more sense now.
 

Bacchus

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Go with EK, but recent literature has contributed about 5-10% of translation to the nucleus. This is all back up by extensive research. However, don't contradict EK but know that nuclear translation exists.
 

isaacmn

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okay, breaking down the question., first when you see nucleus, think transcription because it contains DNA/chromosomes. Post transcriptional modification ( splicing, capping, pola A tail) occurs in the nucleus also but only exons becomes part of the Mature RNA taking to the cytoplasm for translation.

In other not to get you confused with the words "transcription" and "translation", ribosomal RNA are produced in the nucleolus. Are they transcribed or translated...I dont know.

The rough ER ---protein synthesis, so definitely translation can take place there

mitochondria matrix...i dont doubt translation taking place there, because its one of the weird organelle that contains its own DNA and RNA, there're some disease associated with abnomal translation of the ribosomal RNA.


other organelle that could exibit translation are ribosomes ( they contain RrNa and proteins, and functions majorly for protein production)
 

futuredoctor10

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Translation in a eukaryotic cell is associated with each of the following organelles or locations except:

(1) mitochondrial matrix
(2) cytosol
(3) nucleus
(4) the rough ER

Above posters have responded well to this question. Cytosol is where translation occurs on free ribosomes; you can also have translation on ribosomes bound to the rough ER. The mitochondrial matrix does have translation of mitochondrial DNA I believe [someone check me on this]. So by process of elimination, it has to be nucleus.

(Also the nucleus should be associated with transcription of the DNA into mRNA which is transported out of the nuclear pores into the cytosol for translation)

Question: just curious bacchus, what is the 5-10% of "nuclear translation?" That would be an interesting passage for the MCAT to have in the BS, esp since now a days they like throwing new research-based passages from ongoing research in there.
 
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