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Step 1:: Ribosomes are made in the nucleolus, which is a substructure within the nucleus of eukaryotic cells.
The nucleolus is the site of ribosome biogenesis, where ribosomal RNA (rRNA) and ribosomal proteins are assembled to create ribosomes.
Step 2:: The process of ribosome assembly begins in the nucleolus with the transcription of ribosomal DNA (rDNA) genes by RNA polymerase I to produce the initial rRNA transcript.
This transcript contains the sequences for the 18S, 5.8S, and 28S rRNAs.
Step 3:: The rRNA transcript is cleaved and modified to form the mature rRNAs.
During this process, ribosomal proteins are synthesized in the cytoplasm and then transported into the nucleus, where they associate with the maturing rRNAs in the nucleolus.
Step 4:: The assembled rRNAs and ribosomal proteins form small and large ribosomal subunits.
The small subunit, consisting of the 18S rRNA and approximately 30 ribosomal proteins, is responsible for decoding messenger RNA (mRNA). The large subunit, composed of the 5.8S, 28S rRNAs, and around 50 ribosomal proteins, is involved in peptide bond formation during protein synthesis.
Step 5:: Once the small and large ribosomal subunits are formed, they are exported from the nucleolus to the cytoplasm, where they can participate in protein synthesis.
In the cytoplasm, the small and large subunits combine with mRNA and transfer RNA (tRNA) to form a functional ribosome, which translates the genetic code in mRNA into a polypeptide chain.
Final Answer
The nucleolus is the site of ribosome biogenesis, where ribosomal RNA (rRNA) and ribosomal proteins are assembled to create ribosomal subunits, which are then exported to the cytoplasm for protein synthesis.
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