Chapter 11: Gene Expression Control in Division & Development pp

Prokaryotes 1965 Nobel Prize to Jacob & Monod for work on lac operon in E. coli Lactose is metabolized by 3 enzymes in E. coli Genes for these proteins are sequential An operator sits between promoter & these structural genes lac operon = promoter + operator + 3 genes Upstream regulatory gene codes for repressor

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How it works. Regulatory gene codes for repressor protein Repressor protein binds to the operator site Repressor prevents RNA polymerase advancement from its promoter site Repressor protein selectively binds lactose & cannot bind the operator site then Repression is lifted  genes are “turned on” only when lactose is present

Eukaryotic control Control is at level of individual chromosome Euchromatin, uncoiled DNA, is site of active transcription DNA contains bases that code for proteins (exons) & bases that do not (introns) Exons & introns are both transcribed Only exons are translated Introns may serve as regulatory elements

Transcriptional Control Pre-mRNA is full copy of DNA gene’s message Splicesomes (RNA + protein) cut out introns & fuse exons; ribozymes (RNA) also splice Introns regulate RNA, bind to &/ or control expression Exons can code for functional domains Exons can be selected to form specific protein

Transcriptional Control Transcription factors (TF) bind to regulatory elements on DNA, proteins, & other TF – Promoters – Enhancers – Repressors TF recruit RNA polymerase to promoter TF-to-TF binding can change shape of DNA

TF-binding Interactions

Genes for Development Cells differentiate to become specialized – Every zygote has all the DNA – Cells/ tissue specialize in morphogenesis – Cells only express DNA for their functions Homeotic genes dictate loci of anatomy – Specific sequence within gene = “homeobox” Homeotic genes form regulatory proteins – Control which genes are expressed – Control rates of cell division & gene expression

Cancer & Cell Control Proto-oncogenes control normal cell division, growth, & behavior Carcinogen = mutagen  DNA damage Mutated proto-oncogenes  “oncogene” Oncogenes promote uncontrolled growth  tumors (benign or malignant)  cancer Metastasis = spread of CA beyond origin Mutated tumor-suppressor genes  cancer – Mutations in all 3 tumor-suppressor genes + viral oncogene + mutated proto-oncogene

Types of Cancer Carcinomas – Skin & tissues lining organs Sarcomas – Bone & muscle Lymphomas – Lymphatic system’s solid tumors Leukemia – Blood-forming tissues  uncontrolled WBC production