Noncoding RNA roles in Gene Expression

I. Prior Thinking & New Findings A. Protein-coding DNA only accounts for 1.5% of the human genome. B. Most of the rest of the DNA was thought to be noncoding and never transcribed. (therefor useless DNA) C. Recently scientists have found that the genome is transcribed into nonprotein-coding RNAs 1. In the cell there is a large diversity of RNA molecules that play crucial roles in regulating gene expression

II. MicroRNA A. MicroRNA (miRNA) are small single stranded molecules that are capable of binding to complementary sequences in mRNA molecules to either degrade an mRNA molecule or block translation. (thus regulating gene expression)

I. Regulation at Stages A. All organisms prokaryotes and eukaryotes alike have to regulate which genes are expressed. 1. both uni- and multicellular organisms must continually turn genes on and off in response to signals B. All cells have the same genome however, the genes expressed by each cell is unique allowing for cells to carry out specific functions. 1. Cells do not differ in genes present but differential gene expression

II. MicroRNA B. How do miRNA regulate gene expression: 1. Made from larger RNA precursors that fold back on themselves, forming one or more double stranded hairpin structures 2. Each hair pin is cut by an enzyme 3. One side is degraded the other the miRNA forms a complex with proteins 4. The complex can bind to a RNA molecule

III. Small Interfering RNAs A. If cells are injected with double stranded RNA they turned off expression of genes with the same sequences as the RNA. This is called RNA interference (RNAi) which is caused by siRNA. 1. siRNA are very similar to miRNA