Genome
One complete set of genes in an organism (a haploid set).
Except for occasional unrepaired damage to its DNA (= mutations), the genome is fixed.
Transcriptome
The most common definition: All the messenger RNA (mRNA) molecules transcribed from the genome.
Varies with the differentiated state of the cell and the activity of the transcription factors that turn gene transcription on (and off).
Speaking strictly, one would define the transcriptome as all the RNA molecules — which includes a wide variety of untranslated, nonprotein-encoding RNA — transcribed from the DNA of the genome. It is now thought that ~75% of our DNA is transcribed into RNA although only 1.5% of this is messenger RNA for protein synthesis.
Metabolome
All the metabolic machinery, e.g.,
- enzymes
- coenzymes
- small metabolites, like
- the intermediates in glycolysis and cellular respiration
- nucleotides
present in a cell at a given time.
Varies with the differentiated state of the cell and its current activities.
Proteome
The proteome is the protein complement of the genome. It is quite a bit more complicated than the genome because a single gene can give rise to a number of different proteins through
- alternative splicing of the pre-messenger RNAs (pre-mRNAs)
- RNA editing of the pre-messenger RNAs
- attachment of carbohydrate residues to form glycoproteins
- addition of phosphate groups to some of the amino acids in the protein
While we humans probably have only some 21 thousand genes, we probably make at least 10 times that number of different proteins. The great majority of our genes produce pre-mRNAs that are alternatively-spliced.
The study of proteomics is important because proteins are responsible for both the structure and the functions of all living things. Genes are simply the instructions for making proteins. It is proteins that make life.
The set of proteins within a cell varies
- from one differentiated cell type to another (e.g. red blood cell vs lymphocyte) and
- from moment to moment, depending on the activities of the cell, e.g.,
- getting ready to duplicate its genome;
- repairing damage to its DNA;
- responding to a newly-available nutrient or cytokine;
- responding to the arrival of a hormone