Gene Regulation: Prokaryotes and Eukaryotes Chapter 11

Lac Operon OPERON Regulatory gene Promoter Operator DNA mRNA Protein Lactose Promoter Operator Lactose-utilization genes Active repressor RNA polymerase cannot attach to promoter RNA polymerase bound to promoter Inactive repressor Enzymes for lactose utilization OPERON Operon turned off (lactose absent) Operon turned on (lactose inactivates repressor) Regulatory gene

Trp Operon (a) Tryptophan absent, repressor inactive, operon on. RNA polymerase attaches to the DNA at the promoter and transcribes the operon’s genes. Genes of operon Inactive repressor Protein Operator Polypeptides that make up enzymes for tryptophan synthesis Promoter Regulatory gene RNA polymerase Start codon Stop codon trp operon 5 3 mRNA 5 trpD trpE trpC trpB trpA trpR DNA mRNA E D C B A

Trp Operon DNA mRNA Protein Tryptophan (corepressor) Active repressor No RNA made Tryptophan present, repressor active, operon off. As tryptophan accumulates, it inhibits its own production by activating the repressor protein. (b)

Levels of Chromatin Packing

X chromosome Inactivation and Tortoiseshell Cat

Tortiseshell Cat

X chromosome Inactivation in a Calico Cat

Cellular Differentiation Muscle cell Pancreas cells Blood cells

Eukaryotic Transcription: Enhancers, Activators Promoter Gene DNA Activator proteins Other proteins Transcription factors RNA polymerase Bending of DNA Transcription

Production of two different mRNAs from the same gene DNA RNA transcript mRNA Exons or RNA splicing

Alternative Gene Splicing

Overview: Opportunities for gene regulation in eukaryotic cells NUCLEUS Chromosome Gene RNA transcript mRNA in nucleus mRNA in cytoplasm Polypeptide Active protein Breakdown of protein Cleavage / modification / activation Translation Breakdown of mRNA CYTOPLASM Flow through nuclear envelope Splicing Addition of cap and tail Transcription DNA unpacking Other changes to DNA Exon Intron Cap Tail Broken- down mRNA Broken- down protein