Chapter 11: Gene Expression

Control in Division & Developmentpp 217-228

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

lac operon

http://www.phschool.com/science/biology_place/biocoach/lacoperon/regulate.html

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