Final answer:
The satellite regions that distinguish certain chromosomes encode ribosomal RNAs and proteins.
Step-by-step explanation:
The satellite regions that distinguish chromosomes 13, 14, 15, 21, and 22 are repeated genes that encode ribosomal RNAs and proteins. These satellite regions are associated with the nucleolus and are involved in the formation of ribosomes.
These regions are not protein complexes that stabilize the chromosome, nor are they primarily euchromatin or located near the centromere in the context described by the question. Euchromatin is transcriptionally active DNA, whereas heterochromatin, which is found near the centromeres, contains genes that are often not expressed.