Total RNA is all the RNA molecules found in a cell, including messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA), micro RNA (miRNA), siRNA (short interfering RNA) and other non-coding RNAs (ncRNA).
RNA directly codes for amino acids and acts as a messenger between DNA and ribosomes to make proteins, while DNA is responsible for storing and transferring genetic information. Unlike DNA which is double-stranded, RNA is single-stranded and so not as stable as DNA under alkaline conditions. Both DNA and RNA share the same nucleotides for base paring except that DNA uses thymine while RNA uses uracil. Uracil differs from thymine in that it lacks a methyl group on its ring. DNA contains the sugar deoxyribose, while RNA contains the sugar ribose. The difference between these sugars is that ribose has one more -OH group than deoxyribose, which has -H attached to the second carbon in the ring.
An RNA strand is a chain with a nucleotide at each chain link. RNA is often found as a single strand folded onto itself rather than a double-helix-strand.
The main function of RNA is to carry information of amino acid sequence from the genes to where proteins are assembled on ribosomes in the cytoplasm. There are different types of RNA and they all have their functions. For example messenger RNA (mRNA) carries a protein production 'blueprint' from a cell's DNA to the ribosomes, where protein synthesis occurs. Transfer RNA (tRNA) then carries the approprite amino acids into the ribosome for inclusion in the new protein and ribosomal RNA (rRNA) together with ribosomal proteins, makes up the ribosomes, the organelles that translate the mRNA.
An RNAseq library is a compilation of the RNA transcripts or the transcriptome for quantifying, discovery and profiling gene expression. The RNAseq library is created by converting the mRNA and other RNAs into complementary DNA (cDNA) by a reverse transcription enzyme. Adapters are then ligated to the cDNA (during library preparation stage) to make RNAseq libraries, which are then sequenced by a sequencer.