Final answer:
The site where RNA is converted into polypeptides is the ribosomal unit. Ribosomes are made of rRNA and protein subunits and are responsible for translating the mRNA sequence into a sequence of amino acids, creating polypeptides.
Step-by-step explanation:
The site where RNA is converted into polypeptides is the ribosomal unit. Ribosomes are essential cellular structures responsible for protein synthesis. These organelles consist of rRNA and proteins organized into large and small subunits. The mRNA template, derived from DNA transcription in the nucleus, is processed by ribosomes where its sequence of nitrogenous bases is translated into a specific sequence of amino acids, forming polypeptides which eventually fold into functional proteins.
Ribosomes can be found floating freely in the cytoplasm or attached to the endoplasmic reticulum. They function by translating the genetic code into polypeptides through the processes of initiation, elongation, and termination. Transfer RNA (tRNA) molecules bring amino acids to the ribosomes, where they are added to the growing polypeptide chain with the help of enzymatic activity found in the rRNA, particularly the peptidyl transferase activity.