Essential knowledge 3.B.1:

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. • 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. 18-3 trp operon Promoter Promoter Genes of operon DNA trpD trpB trpA trpE trpC trpR Operator Regulatory gene Stop codon Start codon 3 mRNA 5 RNA polymerase mRNA 5 D E C B A Protein Inactive repressor Polypeptide subunits that make up enzymes for tryptophan synthesis (a) Tryptophan absent, repressor inactive, operon on DNA No RNA made mRNA Protein Active repressor Tryptophan (corepressor) (b) Tryptophan present, repressor active, operon off

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.

Fig. 18-3 trp operon Promoter Promoter Genes of operon DNA trpD trpB trpA trpE trpC trpR Operator Regulatory gene Stop codon Start codon 3 mRNA 5 RNA polymerase mRNA 5 D E C B A Protein Inactive repressor Polypeptide subunits that make up enzymes for tryptophan synthesis (a) Tryptophan absent, repressor inactive, operon on Is this negative or positive control? DNA No RNA made mRNA Protein Active repressor Tryptophan (corepressor) (b) Tryptophan present, repressor active, operon off

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

Negative and positive control Mechanisms • http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter16/regulatory_proteins__regulation_by_repression.html

In eukaryotes, gene expression is complex and control involves regulatory genes, regulatory elements and transcription factors that act in concert. 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. 18-9-3 Promoter Activators Gene DNA Distal control element Enhancer TATA box General transcription factors DNA-bending protein Group of mediator proteins RNA polymerase II RNA polymerase II Transcription initiation complex RNA synthesis

Enhancers and repressors • http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter16/transcription_complex_and_enhancers.html

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

Essential knowledge 3.B.2: A variety of intercellular and intracellular signal transmissions mediate gene expression

Signal transmission within and between cells mediates gene expression • Cytokines regulate gene expression to allow for cell replication and division.

Signal transmission within and between cells mediates gene expression • Mating pheromones in yeast trigger mating gene expression. • Two haploid yeast of opposite mating types secrete pheromones, grow projections and mate.

Signal transmission within and between cells mediates gene expression • Ethylene levels cause changes in the production of different enzymes, allowing fruits to ripen.

Signal transmission within and between cells mediates gene expression • Seed germination and gibberellin • Gibberellins (GAs) are plant hormones that regulate growth and influence various developmental processes, including stem elongation, and germination

Signal transmission within and between cells mediates cell function. 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.

Signal transmission within and between cells mediates cell function. • 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

Signal transmission within and between cells mediates cell function. • 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.

Essential knowledge 3.B.1: