Post on 21-Dec-2015
Prokaryotic Gene Regulation
› @To conserve resources, prokaryotes regulate their activities, producing only those genes necessary for the cell to function.@
› 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?)
Prokaryotic Gene Regulation• What is an Operon?
• Group of Genes That Operate Together
• For Example:–E. coli ferments lactose
• 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 lac Operon (lactose Operon)
The Lac Operon @The lac Operon
– Regulates Lactose Metabolism@– 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
Membrane2. Separate The Two Sugars
Promoters and Operators › 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.
Gene Regulation: lac Operon
Key Concept:
The lac Genes Are:Turned Off By Repressors
And
Turned On By The Presence Of Lactose
Eukaryotic Cell Specialization › Most Eukaryotic Genes Are
Controlled Individually And Have Regulatory Sequences That Are Much More Complex Than Prokaryotic Gene Regulation
RNA Interference
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)
RNA Interference
› @Blocking gene expression by means of an miRNA silencing complex is known as RNA interference (RNAi).@
Genetic Control of Development› 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.
Homeotic Genes › 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
Regulation & Development
• Hox Genes– @Control Organ &
Tissue Development In The Embryo@
– Mutations Lead To Major Changes• Drosophila With Legs In Place of Antennae
Regulation & Development
Hox Genes Present In All Eukaryotes– Shows Common Ancestry–Pax 6 hox gene
• Controls eye growth in Drosophila, Mice & Man
• Pax 6 from Mouse Placed In Knee Development Sequence Of Drosophila Developed Into Eye Tissue.Common Ancestor >600M Years Ago
Homeobox and Hox Genes › 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.
Environmental Influences › @In prokaryotes and eukaryotes,
environmental factors can influence gene expression.@ 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.