1 Intro to Gene Regulation Organisms have lots of genetic information, but they don’t necessarily want to use all of it (or use it fully) at one particular time. Eukaryotes: Development, differentiation, and homeostasis –In going from zygote to fetus, e.g., many genes are used that are then turned off. –Liver cells, brain cells, use only certain genes –Cells respond to internal, external signals

2 Gene regulation continued Prokaryotes: respond rapidly to environment –Transcription and translation are expensive Each nucleotide = 2 ATP in transcription Several GTP/ATP per amino acid in translation If protein is not needed, don’t waste energy! –Changes in food availability, environmental conditions lead to differential gene expression Degradation genes turned on to use C source Bacteria respond to surfaces, new flagella etc. Quorum sensing: sufficient # of individuals turns on genes.

3 On/off, up/down, together Sometimes genes are off completely and never transcribed again; some are just turned up or down –Eukaryotic genes typically turned up and down a little compared to huge increases for prokaryotes. Genes that are “on” all the time = Constitutive Many genes can be regulated “coordinately” –Eukaryotes: genes may be scattered about, turned up or down by competing signals. –Prokaryotes: genes often grouped in operons, several genes transcribed together in 1 mRNA.

4 How is gene expression controlled? 1.Transcription: most common step in control. Control at promoter area 2.RNA processing: only in eukaryotes. Alternate splicing changes type/amount of protein. 3.RNA interference Small interfering RNAs cause mRNA destruction

5 Gene regulation (cont.) 1.Translation: prokaryotes, stops transcrp. early. 2.Stability of mRNA: longer lived, more product. 3.Post-translational: change protein after it’s made. Process precursor or add PO 4 group. 4.DNA rearrangements. Genes change position relative to promoters, or exons shuffled.