Final answer:
RNA molecules are much shorter than chromosomal DNA, encoding the genetic information of a single gene. The size of RNA ranges from around 21 nucleotides in length for microRNA to various lengths for mRNA and rRNA, with mRNA being subject to splicing that shortens its length compared to the originating DNA sequence.
Step-by-step explanation:
RNA molecules vary in size, but they are generally much shorter than chromosomal DNA. RNA functions to encode genetic information, often representing just a single gene, which is why the molecules can be comparatively smaller. For instance, microRNA (miRNA) are tiny RNA molecules, about 21 nucleotides in length, that play a role in regulating gene expression by binding to other RNA molecules to degrade them. Meanwhile, transfer RNA (tRNA) is a small, stable RNA typically around 70-90 nucleotides in length, which has important roles in protein synthesis.
Messenger RNA (mRNA), which is the RNA type analyzed most frequently, varies in length but is still much shorter than DNA. It reflects the protein-coding genes being expressed in the cell and leaves the nucleus, unlike DNA – this difference in location is part of why their lengths differ. In addition, during processes like RNA splicing, non-coding regions called introns are removed from the mRNA, thus considerably shortening its length compared to the DNA sequence from which it was transcribed.
Ribosomal RNA (rRNA) is transcribed as a larger precursor in eukaryotes before being processed into smaller units. For example, the 45S precursor transcript is processed into 5.8S rRNA, 18S rRNA, and 28S rRNA – the Svedberg (S) values indicating their relative sizes.