Describe the structure and function of mirna, snrna, and lncrna, which represent the three major types of noncoding rnas; what are four mechanisms by which lncrna molecules are thought to regulate cellular processes?.

MicroRNAs are 18–24 nucleotide short RNA transcripts that control translational gene expression.
The majority of miRNAs are synthesized from DNA sequences into precursor miRNAs (pre-miRNAs), main miRNAs (pri-miRNAs), and mature miRNAs.
miRNAs interact with the 3′ UTR of target mRNAs to suppress expression.

Small nuclear RNAs(snRNA):

The typical length of a snRNA is 150 nucleotides.
snRNAs are found in eukaryotic cells in the Cajal bodies and splicing speckles of the cell nucleus. Either RNA polymerase II or RNA polymerase III transcribes them.

Long noncoding RNAs(lncRNA):

The three domains of the lncRNA are structured into a modular structure with 12 helices, 8 terminal loops, 5 sizable internal loops, and a five-way junction.
lncRNA are epigenetic regulators by modulating histone or DNA modification, primarily methylation and acetylation, and control epigenetic modification primarily in the nucleus, which controls gene transcription at the transcriptional level.
They regulate cellular processes by (i)chromatin remodeling, (ii) preventing the activity of particular transcription factors, (iii), blocking the promoter area of particular genes, (iv), building double-stranded RNA complexes with mRNA or miRNAs, and finally causing gene expression.

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