Chapter 11: Gene Expression

Chapter 11: Gene Expression
Control in Division & Development
pp 217-228
• 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
lac operon
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
• 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
• 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