Transcriptome refers to the entire set of transcripts present in a cell under given conditions. Therefore, it is the entire set of RNA of all types that is being expressed by that cell. As conditions change, such as a change in development and related signals or a change in local environment such as the concentration of a particular molecule, the transcriptome can change. A change in the transcriptome is due to changes in the level of expression (i.e. the amount of product transcribed) of some or all of the RNAs - which can include a complete reduction so that some RNAs are no longer expressed at all - and/or to the expression of new RNAs in the novel conditions.

Over the years we have discovered an increasing number of types of RNA in eukaryotic cells. There is also growing recognition that the prokaryotic transcriptome is fairly complex but much more attention has been paid to eukaryotes. All RNA molecules are generated by transcription and have the same basic structure. However, different types (classes) are referred to by the function of the RNA. The different types are differentiated by lower case letters preceding RNA: so mRNA and tRNA and are two different types. It is important to note that although all RNA molecules are similar in that they are just a string of nucleotides, RNA is usually altered in various ways after being transcribed. Different types are usually altered, or processed, in different ways. When important for our purposes the processing will be covered when we discuss the function of that type of RNA.

The main types of eukaryotic RNA that we cover in our course are:

mRNA	messenger RNA	mRNA transcripts are translated into protein
tRNA	transfer RNA	tRNA plays a role in protein translation
rRNA	ribosomal RNA	rRNA is a component of the ribosome and so it plays a role in protein translation
gRNA	guide RNA	gRNA is involved in RNA editing
snRNA	small nuclear RNA	snRNAs are involved in pre-mRNA splicing

And the following, which are regulatory RNAs

lncRNA	long noncoding RNA	These are regulatory RNA molecules greater than 200 nucleotides in length. This differentiates them from the regulatory RNAs below that are all much less than 200 nucleotides long. Two major subtypes of lncRNA are long intergenic noncoding RNA (lincRNA) and antisense RNA (asRNA). The role that lncRNA plays in regulation is covered here.
miRNA	micro RNA	miRNA is involved in RNA silencing through RNA interference, or RNAi
siRNA	small interfering RNA	Also called short interfering RNA. siRNA is involved in RNA silencing through RNA interference, or RNAi
piRNA	Piwi-interacting RNA	The role of piRNA is discussed here

General Expression

Table of Contents