This document summarizes gene regulation and expression. It defines key terms like genes, genomes, and gene expression. It explains that some genes are continuously expressed while others are only expressed under certain conditions. There are mechanisms that turn genes on and off. Gene regulation is essential for optimal energy use and the growth, development, and existence of organisms. There are two main types of gene regulation: positive regulation which increases gene expression, and negative regulation which decreases it. Regulation can occur during transcription, translation, and post-translation. Prokaryotes provide models for studying gene expression in mammalian cells. In prokaryotes, genes in the same metabolic pathway are often clustered in operons, where a single promoter initiates transcription of multiple