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Control Mechanisms

Control Mechanisms. Transcription Factors. 42,000 genes that exist for proteins in humans. Transcription factors are mechanisms that turn transcription and translation on and off, depending on the need for the protein. This is called gene regulation.

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Control Mechanisms

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  1. Control Mechanisms

  2. Transcription Factors • 42,000 genes that exist for proteins in humans. • Transcription factors are mechanisms that turn transcription and translation on and off, depending on the need for the protein. • This is called gene regulation. • Proteins that are always in need= housekeeping genes.

  3. Gene Regulation Can occur at four levels: • Transcriptional: regulates what gene and the number of copies of a gene that are made. • Post-transcriptional: removal of introns and splicing of exons. • Translational: regulates how often and how fast mRNA is converted into proteins. This controls activation and destruction of mRNA. • Post-translational: addition of various chemical groups (sugars and phosphates)

  4. E.coli and lactose • Negative regulation • Lactose is a disaccharide found in milk. • The bacteria E.colilines the intestines of mammals and uses the energy of lactose for growth. • The energy is released when the protein β-galactosidasebreaks the bond between galactose and glucose. • NO lactose = NO β-galactosidase

  5. Prokaryotic Gene Regulation In bacterial cells gene regulation (such as β-galactosidase) occurs by Operons: • cluster of structural genes • promoter • operator Operator: short regulatory sequence of bases that binds a repressor protein (does not code for structural proteins).

  6. lacOperon Consists of a cluster of three genes that code for proteins involved in lactose metabolism. • lacZ:codes for β-galactosidase • lacY:codes for β-galactosidasepermease(allows lactose to enter through the cell membrane) • lacA: codes for transacetylase

  7. Repression • Lacl protein is a repressor protein • Does not let lacZ make β-galactosidase protein by binding to the lactose operator. • This BLOCKS RNA polymerase by covering part of the promoter region. • When lactose is present it acts as and inducer and binds to Lacl. This complex falls off DNA and now β-galactosidase can be made.

  8. trpOperon • Tryptophan is an amino acid that is also used by E.coli cells for the production of protein (from diet or synthesized). • When there is a high concentration of tryptophan, the genes for making tryptophan are not transcribed. • trp binds to the trp repressor protein acting as a corepressor. This alters its shape and the trp repressor-tryptophan complex can now bind to the operator. This blocks the transcription of tryptophan. • When the concentration of trp is low, trpcorepressor cannot stay bound to the trp repressor protein. This restores the shape of the repressor, which releases from the operator. The gene can now be read.

  9. Gene Regulation lacOperon: • Negative regulation • When lactose is NOT present, the protein (β-galactosidase) is not transcribed. trpOperon: • Positive regulation • When trp IS present, the amino acid is not transcribed.

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