The Need for Gene Expression
Genes are DNA sequences that control traits in an organism by coding for proteins. Organisms such as plants and animals have tens of thousands of genes. The impact that a single gene's information can have on an organism, however, is tremendous. Furthermore, organisms have all of their genes in each of their cells but they only need to use the information from a subset of these genes, depending on the type of cell and the cell’s stage of development. Therefore the key to gene function is controlling its expression.
Figure 1. Proteins made inside cells control development. (Image by D. Namuth-Covert)
Figure 2. Genes are part of chromosomes. (Image by D. Namuth-Covert)
Figure 3. A gene is a sequence of DNA that encodes an RNA. (Image by D. Namuth-Covert)
Its importance is evident when you observe the changes plants go through during their lifecycle or during a season. Trees and bushes, for example, have dormant buds through the winter. Environmental signals affiliated with the coming of spring induce genes in the buds to turn on and drive the dramatic changes of leaf development and flowering. The genes were always present in those bud cells but were controlled to turn on at the proper time. Understanding gene expression thus requires an examination of two processes, the activation of gene expression to make an information message and the reading of this message to build a specific protein.
Figure 4. Gene expression is a two-step process of information transfer in the cell. (Image by D. Namuth-Covert)
Figure 5. In eukaryotes, RNA molecules made in the nucleus, move to the cytoplasm to provide information for the cell to build proteins. (Image by D. Namuth-Covert)