The genome is made up of deoxyribonucleic acid (DNA), a long, winding molecule that contains the instructions needed to build and maintain cells. For these instructions to be carried out, DNA must be transcribed into corresponding molecules of ribonucleic acid (RNA), referred to as transcripts. A transcriptome is a collection of all the transcripts present in a given cell. There are various kinds of RNA. The major type, called messenger RNA (mRNA), plays a vital role in making proteins. In this process, mRNA transcribed from genes, which include the protein-coding parts of the genome, is delivered to ribosomes, which are molecular machines located in the cell's cytoplasm. The ribosomes read, or "translate," the sequence of the chemical letters in mRNA to assemble building blocks called amino acids into proteins. Each mRNA is transcribed from a gene and then translated into a specific protein.. DNA can also be transcribed into other types of RNA that do not code for proteins. Such transcripts may serve to influence cell structure and to regulate genes.
Is a transcriptome the same as a genome?
No, a transcriptome is different from a genome, which is the entire DNA sequence of an organism. A transcriptome represents the very small percentage of the genome - less than 5 percent in humans - that is transcribed into RNA molecules. A gene may produce many different types of mRNA molecules, so a transcriptome is much more complex than the genome that encodes it.
What can a transcriptome tell us?
The sequence of an RNA mirrors the sequence of the DNA from which it was transcribed. Consequently, by analyzing the entire collection of RNAs (transcriptome) in a cell, researchers can determine when and where each gene is turned on or off in the cells and tissues of an organism. Depending on the technique used, it is often possible to count the number of transcripts to determine the amount of gene activity, also called gene expression, in a certain cell or tissue type. In humans and other multi-cell creatures, nearly every cell contains the same genes, but different cells show different patterns of gene expression. These differences are responsible for the many different types of properties and behaviors seen among various cells and tissues, both in health and disease. By collecting and comparing transcriptomes of different types of cells, researchers can gain a deeper understanding of what constitutes a specific cell type, how that type of cell normally functions, and how changes in the normal level of gene activity may reflect or contribute to disease. Furthermore, by aligning the transcriptome of each cell type to the genome, it is possible to generate a comprehensive, genome-wide picture of what genes are active in which cells.