Regulation of Gene Expression Chapter 18 http://learn.genetics.utah.edu/content/cells/scale/

YOU MUST KNOW Genes can be activated by inducer molecules, or they can be inhibited by the presence of a repressor as they interact with regulatory proteins or sequences A regulatory gene is a sequence of DNA that codes for a regulatory protein such as a repressor protein How the components of an operon function to regulate gene expression in both repressible and inducible operons How positive and negative control function in gene expression The impact of DNA methylation and histone acetylation on gene expression How timing and coordination of specific events are regulated in normal development, including pattern formation and induction The role of microRNAs in control of cellular function The role of gene regulation in embryonic development and cancer

Operons Clusters of genes in bacterial chromosomes 3 parts Allows expression of several related genes to be controlled as a unit 3 parts Operator – controls access of RNA polymerase to genes Found within the promoter or between the promoter and the coding genes Promoter – where RNA Polymerase attaches Genes

Regulatory genes Located a distance away from the operon Code for proteins that may bind to the operator When that protein occupies the operator, RNA Polymerase cannot access genes of the operon (genes turned off)

Repressible Operons Usually on and generally anabolic (build essential biomolecules) Repressor protein produced from regulatory gene is inactive Biomolecules coded for by the operon acts as a co-repressor – binds to the repressor and activates it So if biomolecule is already present in the cell, the operon is turned off

Inducible Operons Normally off and generally catabolic (break down molecules) Repressor protein produced by regulatory gene is active In order to deactivate the repressor protein, an inducer must be present – when inducer is bound to repressor, it can’t block transcription of the operon

Eukaryotic Gene Expression Differential Gene Expression – expression of different genes in different cells DNA methylation – addition of methyl groups to DNA, reducing gene expression Histone acetylation – acetyl groups added to histones, loosening the coiling of nucleosomes, increasing expression

Transcription initiation – regulation of the binding of transcription factors Transcription initiation complex – enhances gene expression Enhancer regions – DNA sequences far from the gene (enhancer regions) produce proteins called activators

Other mechanisms in eukaryotes Epigenetic inheritance – inheritance of traits by mechanisms not directly involved with nucleotide sequence (environmental factors turn on/off genes) mRNA and protein processing Coordination of gene expression of related genes – genes for one metabolic pathway may be scattered on different chromosomes, but they share the same control elements

Noncoding RNAs RNA interference Micro RNAs (miRNA) and small interfering RNAs (siRNA) bind to mRNA and either degrade it or block its translation

Cell Differentiation Development of the zygote Cell division – repeated mitosis to increase the number of cells Cell differentiation – cells become specialized in structure and function Morphogenesis – organism gains it shape

Cytoplasmic determinants – maternal substances in the egg that influence early development Uneven distribution around cells of the embryo

Determination – series of events that cause differentiation Cell-to-cell signals – molecules produced by one cell influence neighboring cells Induction – signal from a neighboring cell causes cell to differentiate Determination – series of events that cause differentiation Induction

Pattern formation Sets up body plan for the developing organism (head, tail, left, right, etc.) Morphogens – substances that determine these axes (unevenly distributed) Homeotic genes – master control genes for pattern formation

Cancer and cell cycle genes Oncogenes – cancer causing genes Proto-oncogenes – code for proteins responsible for normal cell growth – become oncogenes when mutated

Tumor-suppressor genes – products normally inhibit cell division p53 gene – product suppresses cancer in four ways Can activate the p21 gene – product halts the cell cycle by binding to cyclin-dependent kinases. This allows DNA to be repaired before cell division Activates miRNAs that inhibit the cell cycle Turns on genes involved in DNA repair When DNA damage is too large to repair, activates genes which cause apoptosis Note: embryonic development is an example of gene regulation done correctly, cancer is when gene regulation goes wrong