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GENE REGULATION HOW DOES A CELL KNOW? which gene to EXPRESS & which gene should stay SILENT? GENE REGULATION When a gene is EXPRESSED, it is transcribed into mRNA. When a gene is SILEN T, it is NOT transcribed. EXPRESSED GENE = TRANSCRIBED SILENT GENE = NOT TRANSCRIBED GENE REGULATION Why would a cell NOT want to express a gene? – Wastes energy & materials ATP GENE REGULATION Cells regulate what genes are expressed based on what protein the cell NEEDS. GENE REGULATION Where does regulation occur? At what step? Most regulation occurs at the DNA to RNA step—transcription! Why? Conserves the most energy! GENE REGULATION—HOW? Expression is regulated by: Promoters Start & Stop Base Pair Sequences Regulatory Sites called Operators GENE REGULATION--PROMOTERS What is a promoter? Specific DNA base pair sequence that provides a binding site for RNA polymerase. “Promotes” or allows transcription to occur GENE REGULATION-START AND STOP BASE PAIR SEQUENCES What do they do? Control where transcription starts and stops. If changed (mutated), transcription is altered. AUG UAA UAG UGA GENE REGULATION-OPERATORS What is an operator? Like an on/off switch. Proteins bind to the operator to regulate transcription. GENE REGULATION-REPRESSORS What is a repressor protein? Binds to the operator to physically blocks the RNA polymerase from the promoter site. BINDS HERE BLOCKS THE PROMOTER GENE REGULATION-ENHANCERS What is an enhancer protein? BINDS HERE Binds to the operator to enhance binding of the RNA polymerase to the promoter site. ENHANCES BINDING TO THE PROMOTER GENE REGULATION IS DIFFERENT IN PROKARYOTES AND EUKARYOTES, WHY? Discuss with the person next to you. Prokaryotic DNA Eukaryotic DNA PROKARYOTIC GENE REGULATION In prokaryotes, genes are organized into operons. What is an operon? A group of genes that code for the same function, and are regulated by the same promoter and operator. One promoter/operator controls the expression of multiple genes. EUKARYOTIC GENE REGULATION Eukaryotic DNA has exons and introns. What are exons? The coding regions of DNA that are expressed into proteins. What are introns? Non-coding regions of the DNA. EUKARYOTIC GENE REGULATION EUKARYOTIC GENE REGULATION CELL DIFFERENTIATION CELL DIFFERENTIATION One chromosome may have several genes. Not all the genes will be transcribed and translated. The genes that are transcribed and translated determine the type of cell. CELL DIFFERENTIATION So these cells all have the exact same DNA, but each cell uses different segments of the DNA during transcription.