Table 1.

Classification of non-coding RNAs.

Non-coding RNAs		Definition
1. Structural non-coding RNAs	tRNA and rRNA	A) The tRNA, 70–87 nucleotides in length, plays critical roles in translation by transferring amino acids to initialize and elongate peptides (38). B) In eukaryotes the cytoplasmic ribosomal RNAs (rRNAs) are the 5S (~120 nucleotides), the 5.8S (~150 nucleotides), the 18S (~1800 nucleotides) and the 28S (~4000 to 5000 nucleotides). Play critical role in protein synthesis (39).
2. Regulatory non-coding RNA	2.1. small non-coding RNAs: microRNA (miRNA), Piwi-interacting RNA (piRNA), Small interfering RNA (siRNA), Centromere repeat associated small interacting RNA (crasiRNAs), telomere-specific small RNA (telsRNAs) (40).	Size between 20–50 nucleotides, play critical roles in multiple regulatory processes, including transcription, post-transcription, and translation. miRNAs: are small non-coding RNAs that span between 18-24 nucleotides. miRNAs regulate gene expression on a post-transcriptional level. miRNAs modulate and orchestrate cellular pathways, including cell growth, autophagy, apoptosis, autophagy, and migration pathway (18, 41).
	2.2. medium non-coding RNA: small nucleolar RNA (snoRNA), transcription initiation RNA (tiRNA), small nuclear RNA (snRNA), small cytoplasmic RNA (scRNA), PROMPTs (40).	Size between 50–200 nucleotides (40).
	2.3. long non-coding RNAs: 2.3.1. Biogenesis: Intronic RNA, Enhancer RNA, Promoter RNA, Antisense RNA, Sense RNA, Intergenic RNA, Bidirectional RNA (40). 2.3.2. Structure: a) Linear lncRNA, b) Circular lncRNA, c) Long intergenic noncoding RNAs (lincRNA), enhancer-derived RNAs (eRNAs), transcribed ultraconserved RNAs (TUCRNAs), Natural antisense transcript (NATs) (40). 2.3.3. Action: cis-acting long non coding RNA (cis-lncRNA), competing endogenous RNA (ceRNA), trans-acting long non coding RNA (trans-lncRNA) (40).	Size greater than 200 nucleotides (40).