Final answer:
28S, 18S, and 5.8S are sedimentation rates of eukaryotic ribosomal RNAs, measured in Svedberg units, and represent the components of the ribosomal subunits after RNA polymerase I transcribes and cleaves the 45S precursor rRNA in the nucleolus.
Step-by-step explanation:
The numbers 28S, 18S, and 5.8S refer to the sedimentation rates of the eukaryotic ribosomal RNAs (rRNAs) that are part of the ribosome structure. The 'S' in these numbers stands for Svedberg units, which are a measure of the rate at which particles sediment when subjected to centrifugal force.
Ribosomal RNA Processing in eukaryotic cells involves the transcription of a 45S precursor rRNA by RNA polymerase I.
This 45S precursor contains the sequences for 18S, 5.8S, and 28S rRNAs, which are eventually cleaved into their functional forms and assembled into ribosomes.
These rRNAs are essential components of the ribosome, with 18S rRNA being part of the 40S small subunit of the 80S ribosome, while 28S and 5.8S rRNAs are part of the 60S large subunit. The precursor rRNA is transcribed from multiple rDNA genes located on acrocentric chromosomes within a specialized structure called the nucleolus.