Chapter 1 - RNA and the cellular biochemistry revisited

Abstract

This chapter focuses on the forms and functions of ribonucleic acid (RNA) and its synthesis by transcription. RNA is a long, unbranched polymer of ribonucleoside monophosphate moieties joined together by phosphodiester linkages, and both eukaryotic and prokaryotic RNAs are essentially single-stranded molecules. RNA molecules are produced by the process of transcription, the process by which a single-stranded RNA molecule is synthesized from a specific chromosome locus. There are important organizational differences associated with genes and the ensuing RNA molecule that results from the transcription when comparing prokaryotic and eukaryotic organisms. The synthesis of RNA is mediated by the activity of enzymes known as RNA polymerases. These transcripts observed within a cell are traditionally classified as ribosomal RNA (rRNA), transfer RNA (tRNA), heterogeneous nuclear RNA (hnRNA), or messenger RNA (mRNA). Important new classes of RNA have been discovered, including microRNA (miRNA), circular RNA (circRNA), and short and long noncoding RNA (ncRNA). The mRNA subpopulation drives the phenotype of the cell, although it is the least abundant of all transcript types and the expression of which is tightly coupled to the expression of other regulatory transcripts. Genes are under the influence of promoters that up- or down-regulate transcription as needed. Gene expression is controlled at four major control points: transcriptional regulation, posttranscriptional regulation, translational regulation, and posttranslational regulation.