RNA location in cell

Inside which of the following cellular compartments can mRNA, tRNA and rRNA all be found?

  1. Mitochondrion
  2. Rough endoplasmic reticulum
  3. Nucleus
  4. Cytosol

A. 1 and 2 only

B. 2 and 3 only

C. 3 and 4 only

D. 1, 3 and 4 only

E. All of them

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I think mRNA, tRNA and rRNA can be found in all the given structures:

  1. Mitochondria has it’s own ribosomes and ribosomes are composed of rRNA and proteins also during the translation in the mitochondrial matrix mRNA And tRNA are also present so it makes sense.

  2. During translation in the cytoplasm a special protein binds to the ribosomes which transports it to the ER where further polypeptide synthesis and modifications takes place so these RNA’s can be present inside of a RER.

  3. In nucleus we have nucleolus which is the assembly unit of ribosomes(rRNA+proteins) also mRNA is formed as a result of transcription in the nucleus which after splicing moves to the cytoplasm Nucleus also have tRNA.

  4. cytosol also makes sense.
    Is it E kindly correct me if i’m wrong.

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The key says it’s D.I do not understand why they exempt RER.

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Ya i am also confused as question says “can” so don’t we consider every possibility associated with it.
As ribosomes are attached to the RER not basically inside it but if we consider the situation where protein synthesis being done inside RER(during secretory pathway) then ribosomal subunits are indeed present.


to me the ribosomes don’t enter the ER or golgi at any step in the secretory pathway, same for the mRNA and tRNA
protein synthesis in done on the external membrane of the ER not inside of it, golgi and ER also modifiy the protein further but this doesn’t involve RNA
at what part of the secretory pathway would you say ribosomal subunits are inside the ER??

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I think you are right what actually it means maybe by translation being inside the RER is modification not synthesis of Polypeptides.
Ari also made a video regarding Polypeptide recognition sequence in the Summer course under Quick review:)

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Thanks i’ll check it out!

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Is it correct that the translated polypeptide goes from the exterior of RER to the lumen inside RER, where it can be folded and packaged into vesicles, so later it can be transported into Golgi apparatus?

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Yes it would be correct,
Translation: The tRNA molecule brings the codon to the Ribosomes attached on the peripheral of the Rough Endoplasmic Reticulum. Once Synthesized the amino acid (polypeptide chain) moves INTO the Rough Endoplasmic reticulum where it moves through the EndoMembrane System.

After post translational modification (Occurs in ER/ Golgi but for this purpose we are talking about simply the ER) proteins and lipids are carried from the ER to the Golgi in transport vesicles that bud from the membrane of the ER and then fuse to to the golgi.

In short, assembled proteins in the ER are packaged into transport vesicles that pinch off from the ER membrane. The vessicles move to the Microtubule which carry them to the Golgi.

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Thank you very much Kyle!