How Does A Cell Know? Which Gene To Express Which Gene To Express& Which Gene Should Stay Silent? Which Gene Should Stay Silent?

conserve resources, prokaryotes regulate their activities, producing only those genes necessary for the cell to (why waste energy if you already have food?) › It would be wasteful for a bacterium to produce enzymes that are needed to make a molecule that is readily available from its environment. (why waste energy if you already have food?)

What is an ? What is an Operon ? Group of Genes That Operate Together Group of Genes That Operate Together For Example: For Example: – E. coli ferments lactose To Do That It Needs Three Enzymes (Proteins), It Makes Them All At Once! To Do That It Needs Three Enzymes (Proteins), It Makes Them All At Once! – 3 Genes Turned On & Off Together. This is known as the – 3 Genes Turned On & Off Together. This is known as the lac Operon (lac tose Operon)

@The lac Operon – Regulates Lactose – It Turns On Only When Lactose Is Present & Glucose is Absent – It Turns On Only When Lactose Is Present & Glucose is Absent. Lactose is a Disaccharide – A Combination of Galactose & Glucose To Ferment Lactose E. coli Must: 1.Transport Lactose Across Cell Membrane 2.Separate The Two Sugars

› The first is a promoter (P), which is a site where RNA-polymerase can bind to begin transcription. › The other region is called the operator (O), which is where the lac repressor can bind to DNA.

Key Concept Key Concept : The lac Genes Are: Turned Off By Repressors And And Turned On By The Presence Of Lactose

› Most Eukaryotic Genes Are Controlled Individually And Have Regulatory Sequences That Are Much More Complex Than Prokaryotic Gene Regulation

 For years, biologists wondered why cells that contain lots of small RNA molecules, only a few dozen bases long, and don’t belong to any of the major groups of RNA (mRNA, tRNA, or rRNA)

gene expression by means of an miRNA silencing complex is known as RNA interference

› As an embryo develops, different sets of genes are regulated by transcription factors, enhancers, and repressors. › Gene regulation helps cells undergo differentiation, becoming specialized in structure and function.

› Edward B. Lewis was the first to show that a specific group of genes controls the identities of body parts in the embryo of the common fruit fly. › Lewis found that a mutation in one of these genes actually resulted in a fly with a leg growing out of its head in place of an antenna! › These master control genes, homeobox genes, activate genes important in cell development

Hox Genes Hox Genes Organ & Tissue Development In The – Mutations Lead To Major Changes Drosophila With Legs In Place of Antennae Drosophila With Legs In Place of Antennae

Hox Genes Present In All Eukaryotes – Shows Common Ancestry – Pax 6 hox gene Controls eye growth in Drosophila, Mice & Man Controls eye growth in Drosophila, Mice & Man Pax 6 from Mouse Placed In Knee Development Sequence Of Drosophila Developed Into Eye Tissue. Pax 6 from Mouse Placed In Knee Development Sequence Of Drosophila Developed Into Eye Tissue. Common Ancestor >600M Years Ago

› Nearly all animals, share the same basic tools for building the different parts of the body. › Common patterns of genetic control exist because all these genes have descended from the genes of common ancestors.

prokaryotes and eukaryotes, environmental factors can influence gene Ex: temperature, salinity, nutrient availability › Ex: The lac operon in E. coli is switched on only when lactose is the only food source in the bacteria’s environment.

1. rRNA 2. tRNA 3. mRNA 4. miRNA

 The Lac operon turns off

 The Lac operon turns on

1. miRNA 2. Homeobox Genes 3. Operator 4. Promoter