Essential Knowledge 3.B.1

Gene regulation results in differential gene expression, leading to cell specialization.

Both DNA regulatory sequences, regulatory genes, and small regulatory RNAs are involved in gene expression. Regulatory sequences are stretches of DNA that interact with regulatory proteins to control transcription. Examples of regulatory sequences include promoters, terminators, and enhancer. A regulatory gene is a sequence of DNA encoding a regulatory protein or RNA.

Both positive and negative control mechanisms regulate gene expression in bacteria and viruses. The expression of specific genes can be turned on by the presence of an inducer. The expression of specific genes can be inhibited by the presence of a repressor. Inducers and repressors are small molecules that interact with regulatory proteins and/or regulatory sequences. Regulatory proteins inhibit gene expression by binding to DNA and blocking transcription (negative control). Regulatory proteins stimulate gene expression by binding to DNA and stimulating transcription (positive control) or binding to repressors to inactivate repressor function. Certain genes are continuously expressed; that is, they are always turned “on,” e.g., the ribosomal genes.

In eukaryotes, gene expression is complex and control involves regulatory genes, regulatory elements and transcription factors that act in concert. Transcription factors bind to specific DNA sequences and/or other regulatory proteins. Some of these transcription factors are activators (increase expression), while others are repressors (decrease expression). The combination of transcription factors binding to the regulatory regions at any

one time determines how much, if any, of the gene product will be produced.

Gene regulation accounts for some of the phenotypic differences between organisms with similar genes.

Students should be able to:

LO 3.18 Describe the connection between the regulation of gene expression and observed differences between different kinds of organisms.

LO 3.19 Describe the connection between the regulation of gene expression and observed differences between individuals in a population.

LO 3.20 Explain how the regulation of gene expression is essential for the processes and structures that support efficient cell function.

LO 3.21 Use representations to describe how gene regulation influences cell products and function.