Living things can be studied and classified based on their genome as well as the protein products derived from those genetic instructions. Here is an explanation of the relationship between genetic instructions and the products of those instructions-clarification of the difference between the cellular genome, proteome and metabolome.
* What Is a Genome? *
The genome of cellular organisms (things that are alive) consists of the nucleic acid deoxyribonucleic acid (DNA). Nucleic acids are large organic molecules made of smaller molecules called nucleotides. Each nucleotide is a monomer, or building block of nucleic acid and consists of 3 portions:
* a pentose sugar
* one or more phosphate groups
* one of four cyclic nitrogenous bases
The only thing that differs from one DNA nucleotide to the next is the type of base it includes. The sequence of these bases, in a DNA molecule is the genetic code, the information that is read and translated into protein molecules used in cell structure and function.
* What Is a Proteome? *
Since DNA is the code, or blueprint, for the construction of cellular proteins, the proteins that an organism can make are limited to those encoded in their genome. The proteome is the full complement of proteins produced by a particular genome.
The genome of an organism is essentially static. It only changes when a mutation occurs. In contrast the proteome continually changes in response to external and internal events. Genes can be ‘turned on’ and ‘turned off’, to make proteins only when the cells require them. In other words, the instructions for making all of an organism’s cellular proteins are always there. However, those instructions are not all simultaneously being carried out.
For example, beta-lactamase is an enzyme, a molecule made primarily of protein, which penicillin resistant Gram-positive bacteria are able to produce. This enzyme is only produced in the presence of penicillin, and, when produced, it breaks up the penicillin molecule so that it can no longer inhibit bacteria. Cells are efficient little machines, and are not prone to waste resources when they are not needed. So although the code for a cell’s proteome is always there, all of the proteins coded for by the DNA are not always present.
* What Is a Metabolome? *
Metabolome is all of the metabolites produced by a single organism. Metabolites are substances required for, or produced by the biochemical reactions of metabolism that occur within the cells of a living organism. Like the proteome, the metabolome is closely tied to an organism’s genome, but is also influenced by which genes are transcribed as well as materials that the cell can obtain from its environment. The study of metabolomes enables scientists to look at the relationship between an organism’s genotype and phenotype and also the relationship between its genotype and environment.
In microbiology identification of the metabolites that an organism can produce is useful in its identification. For example, differential media are used for growing and identifying certain types of bacteria in Petri dishes. A specialized medium called MacConkey’s (MAC) is used to grow Gram-negative bacteria. This medium also contains the sugar lactose and a pH sensitive dye that turns the bacterial colonies pink if they are able to metabolize lactose.
For more information on proteomes and metabolmes, see the Human Metabolome Project, and the article “Thinking Bigproteome Studies in a Post-genome Era”. The information presented in this article was researched from these sources.
