Download
1 / 10
100 likes | 230 Views
Lesson Overview. 13.4 Gene Regulation and Expression. The Lac Repressor Blocks Transcription. When lactose is not present, the lac repressor binds to the O region, blocking the RNA polymerase from reaching the lac genes to begin transcription.
E N D
Lesson Overview 13.4 Gene Regulation and Expression
The Lac Repressor Blocks Transcription • When lactose is not present, the lac repressor binds to the O region, blocking the RNA polymerase from reaching the lac genes to begin transcription. • When lactose is present, it attaches to the lac repressor and changes the shape of the repressor protein in a way that causes it to fall off the operator.
Eukaryotic Gene Regulation • Eukaryotic gene expression is also regulated by DNA binding proteins, however, eukaryotes typically regulate individual genes, not groups of them. • TATA box – short sequence of DNA that marks the beginning of a gene; used to help position RNA polymerase
Gene Expression in Eukaryotes • Transcription factors – proteins that help regulate gene expression by binding DNA promoter/enhancer sequences and blocking or activating transcription. • Promoter/enhancer – sequences of DNA with binding sites for multiple transcription factors.
RNA Interference • Not all genes are expressed in all eukaryotic cells. • Cells in multicellular organisms contain all of the organism’s DNA, yet they only transcribe and translate part of it. • Ex. Liver cells only transcribe and translate liver specific genes while skin cells only transcribe and translate skin specific genes. • RNA interference (RNAi) – used to regulate gene expression in eukaryotes. • During RNAi, microRNAs (miRNAs) bind to transcribed mRNA to block it from being translated into protein. • An enzyme called the “Dicer” enzyme cuts, or dices, these double-stranded loops into microRNA (miRNA), each about 20 base pairs in length. The two strands of the loops then separate.
The Promise of RNAi Technology • The discovery of RNAi has made it possible for researchers to switch genes on and off at will, simply by inserting double-stranded RNA into cells. • The Dicer enzyme then cuts this RNA into miRNA, which activates silencing complexes. • These complexes block the expression of genes producing mRNA complementary to the miRNA. • RNAi technology is a powerful way to study gene expression in the laboratory. It also holds the promise of allowing medical scientists to turn off the expression of genes from viruses and cancer cells, and it may provide new ways to treat and perhaps even cure diseases.
Homeotic Genes • Homeotic Genes- set of master control genes that regulate organs that develop in specific parts of the body.
Homeobox and Hox Genes • Homeobox genes – code for transcription factors that activate other genes important for development and differentiation. • In flies, these are called Hox genes. Hox genes determine the identities of each segment of a fly’s body. • A mutation in one of these genes can completely change the organs that develop in specific parts of the body.
Environmental Influences • In prokaryotes and eukaryotes, environmental factors like temperature, salinity, and nutrient availability can influence gene expression. • Metamorphosis involves a series of transformations from one life stage to another, such as the transformation of a tadpole to an adult bullfrog. It is typically regulated by a number of external (environmental) and internal (hormonal) factors. • For example, under less than ideal conditions—a drying pond, a high density of predators, low amounts of food— tadpoles may speed up their metamorphosis. • The speed of metamorphosis is determined by various environmental changes that are translated into hormonal changes, with the hormones functioning at the molecular level. • gene expression
