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What is the function of a nucleolus?

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Quick Answer

The function of the nucleolus is to transcribe DNA into ribosomal RNA and assemble rRNA into ribosomal subunits. The creation of rRNA is important because rRNA makes up ribosomes which are responsible for protein synthesis in the cell.

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What is the function of a nucleolus?
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Full Answer

In order for transcription to occur, a protein called RNA polymerase binds to DNA at its promoter region. Transcription factors and proteins pull apart DNA's double helix so that polymerase can then transcribe one strand of the DNA to create single-stranded RNA. Transcription ends when polymerase reaches a terminator sequence on the DNA.

When DNA is transcribed into rRNA in the nucleolus, three or four (depending on the organism) distinct rRNAs are produced. These rRNAs are combined with proteins in order to assemble a large ribosomal subunit and a small ribosomal subunit. The subunits are then exported from the nucleolus and nucleus to the endoplasmic reticulum and the cell's cytosol in order to carry out the process of translation, or protein synthesis.

Nucleoli are made of proteins, DNA and RNA and are contained within the cell's nucleus. They don't have membranes, so they can disassemble when the cell divides during mitosis. While humans only have one nucleolus per cell, other organisms exist that can have cells containing multiple nucleoli.

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