For our bodies to have different types of cells, there has to be some mechanism for controlling the expression of our genes. In some cells, certain genes are turned off, while in other cells they are transcribed and translated into proteins. Transcription factors are one of the most common tools that our cells use to control gene expression.
A Brief Definition
Transcription factors (TFs) are molecules involved in regulating gene expression. They are usually proteins, although they can also consist of short, non-coding RNA. TFs are also usually found working in groups or complexes, forming multiple interactions that allow for varying degrees of control over rates of transcription.
Turning Genes Off and On
In people (and other eukaryotes), genes are usually in a default "off" state, so TFs serve mainly to turn gene expression "on." In bacteria, the reverse is often true, and genes are expressed "constitutively" until a TF turns it "off." TFs work by recognizing certain nucleotide sequences (motifs) before or after the gene on the chromosome (up- and downstream).
Genes and Eukaryotes
Eukaryotes often have a promoter region upstream from the gene, or enhancer regions up or downstream from the gene, with certain specific motifs that are recognized by the various types of TF. The TFs bind, attract other TFs and create a complex that eventually facilitates binding by RNA polymerase, thus beginning the process of transcription.
Why Transcription Factors Are Significant
Transcription factors are only one of the means by which our cells express different combinations of genes, allowing for differentiation into the various types of cells, tissues, and organs that make up our bodies. This mechanism of control is extremely important, especially in light of the findings of the Human Genome Project that we have fewer genes in our genome, or on our chromosomes, than originally thought.
What this means is different cells have not arisen from differential expression of completely different sets of genes, but are more likely to have varying levels of selective expression of the same groups of genes.
The Cascade Effect
TFs can control gene expression by creating a "cascade" effect, wherein the presence of small amounts of one protein triggers the production of larger amounts of a second, which triggers production of even larger amounts of a third, and so on. The mechanisms through which significant effects are induced by small amounts of the initial material or stimulus are the basic models of today's biotechnological advances in Smart Polymer research.
Gene Expression and Life Expectancy
Manipulating TFs to reverse the cell differentiation process is the basis of methods for deriving stem cells from adult tissues. The ability to control gene expression, along with knowledge obtained from studying the human genome and genomics in other organisms, has led to the theory that we can prolong our lives if we just control the genes that regulate the aging process in our cells.