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

Regulatory sequences are stretches of DNA that interact with regulatory proteins to control transcription. Promoters Terminators Enhancers  A regulatory gene is a sequence of DNA encoding a regulatory protein or RNA.  Find the regulator gene on the next slide. What does it do?

Fig Polypeptide subunits that make up enzymes for tryptophan synthesis (b) Tryptophan present, repressor active, operon off Tryptophan (corepressor) (a) Tryptophan absent, repressor inactive, operon on No RNA made Active repressor mRNA Protein DNA mRNA 5 Protein Inactive repressor RNA polymerase Regulatory gene Promoter trp operon Genes of operon Operator Stop codon Start codon mRNA trpA 5 3 trpR trpE trpD trpC trpB ABC D E

 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.

Fig Polypeptide subunits that make up enzymes for tryptophan synthesis (b) Tryptophan present, repressor active, operon off Tryptophan (corepressor) (a) Tryptophan absent, repressor inactive, operon on No RNA made Active repressor mRNA Protein DNA mRNA 5 Protein Inactive repressor RNA polymerase Regulatory gene Promoter trp operon Genes of operon Operator Stop codon Start codon mRNA trpA 5 3 trpR trpE trpD trpC trpB ABC D E Is this negative or positive control?

Fig. 18-4a (a) Lactose absent, repressor active, operon off DNA Protein Active repressor RNA polymerase Regulatory gene Promoter Operator mRNA 5 3 No RNA made lac I lacZ Is this positive or negative control?

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1. Transcription factors bind to specific DNA sequences and/or other regulatory proteins. 2. Some of these transcription factors are activators (increase expression), while others are repressors (decrease expression). 3. 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.

Fig Enhancer TATA box Promoter Activators DNA Gene Distal control element Group of mediator proteins DNA-bending protein General transcription factors RNA polymerase II RNA polymerase II Transcription initiation complex RNA synthesis

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

A variety of intercellular and intracellular signal transmissions mediate gene expression

 Cytokines regulate gene expression to allow for cell replication and division.

 Mating pheromones in yeast trigger mating gene expression.  Two haploid yeast of opposite mating types secrete pheromones, grow projections and mate.

 Ethylene levels cause changes in the production of different enzymes, allowing fruits to ripen.

 Seed germination and gibberellin  Gibberellins (GAs) are plant hormones that regulate growth and influence various developmental processes, including stem elongation, and germination

Ex 1: HOX genes and their role in development.  Hox genes are a group of related genes that control the body plan of the embryo along the anterior-posterior (head-tail) axis.

 Ex 2: P53 is a tumor suppressor protein  p53 is crucial in multicellular organisms, where it regulates the cell cycle and, thus, functions as a tumor suppressor that is involved in preventing cancer.  As such, p53 has been described as "the guardian of the genome because of its role in conserving stability by preventing genome mutation

 Morphogenesis “shape” and beginnign--is the biological process that causes an organism to develop its shape  Example 3: morphogen is a substance governing the pattern of tissue development in the process of morphogenesis, and the positions of the various specialized cell types within a tissue.  More precisely, a morphogen is a signaling molecule that acts directly on cells to produce specific cellular responses depending on its local concentration.