MCAT Biology : Nucleus and Nucleolus

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

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Example Question #1291 : Biology

Which of the following is true of the RNA transcripts in the nucleolus and nucleus? 

Possible Answers:

Translation of nuclear transcripts occurs in the cytoplasm, whereas translation of nucleolar transcripts occurs in nucleoplasm

None of these are true

Translation of nuclear transcripts occurs in the nucleoplasm, whereas translation of nucleolar transcripts occurs in the cytoplasm

Translation of both transcripts occurs in the cytoplasm

Correct answer:

None of these are true

Explanation:

In the nucleolus, the transcripts synthesized are rRNA molecules. The unique aspect of rRNA molecules is that they are never converted to proteins; therefore, they never undergo translation. The rRNA molecules synthesized by the nucleolus are assembled with other proteins to create ribosomes; they themselves never undergo translation.

Transcription in the rest of the nucleus produces mRNA molecules that enter the cytoplasm and undergo translation to create proteins.

Example Question #11 : Nucleus And Nucleolus

The nucleolus is responsible for synthesis of which of the following compounds?

Possible Answers:

Arachidonic acid

rRNA

None of these

DNA

tRNA

Correct answer:

rRNA

Explanation:

The nucleolus has genes for transcribing ribosomal RNA. RNA polymerase I in the nucleolus transcribes the gene for ribosomal RNA and causes formation of ribosomal complexes. mRNA and tRNA are transcribed elsewhere in the nucleus and use RNA polymerase II and III, respectively. Arachidonic acid is an omega-6 polyunsaturated fatty acid, which plays roles in cell-signaling, prostaglandin synthesis, and the immune response, and is synthesized in the cytosol.

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