Control Mechanisms Four Levels of Control of Gene

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Control Mechanisms

Control Mechanisms

Four Levels of Control of Gene Expression Type of Control Transcriptional Description n Regulates

Four Levels of Control of Gene Expression Type of Control Transcriptional Description n Regulates which genes are transcribed. n Controls rate of transcription. Posttranscriptional n Modification of m. RNA. n Introns removed & exons spliced together.

Four Levels of Control of Gene Expression Type of Control Translational Description n Controls

Four Levels of Control of Gene Expression Type of Control Translational Description n Controls rate of translation. n Controls rate of m. RNA activation and destruction. Posttranslational n Controls rate at which a protein becomes active and the time it remains functional.

The lac Operon E. coli uses β-galactosidase to break down lactose in order to

The lac Operon E. coli uses β-galactosidase to break down lactose in order to grow. n The 3 genes for β-galactosidase are part of the lac operon. n

The lac Operon n When lactose is absent: ¨ Lac. I repressor protein binds

The lac Operon n When lactose is absent: ¨ Lac. I repressor protein binds to the operator and partially blocks the promoter. ¨ Prevents transcription of the lac operon genes.

The lac Operon n With sufficient lactose: ¨ Binds to the Lac. I repressor

The lac Operon n With sufficient lactose: ¨ Binds to the Lac. I repressor protein. ¨ Lac. I changes its shape, allowing transcription of the lac operon genes. WATCH THIS!!!

The trp Operon E. coli uses tryptophan for the production of protein. n The

The trp Operon E. coli uses tryptophan for the production of protein. n The trp operon consists of 5 genes that code for 3 enzymes needed to synthesize tryptophan. n

The trp Operon n When tryptophan is absent: ¨ The shape of the trp

The trp Operon n When tryptophan is absent: ¨ The shape of the trp repressor protein changes. ¨ No longer binds to the trp operator. ¨ RNA polymerase transcribes trp operon genes.

The trp Operon n With sufficient tryptophan: ¨ Binds to the trp repressor protein,

The trp Operon n With sufficient tryptophan: ¨ Binds to the trp repressor protein, causing a change in shape. ¨ trp repressor-tryptophan complex binds to the operator. ¨ Prevents transcription of the trp operon genes. WATCH THIS!!!

Summary lac Operon n Transcription induced when high levels of lactose present. n Effector

Summary lac Operon n Transcription induced when high levels of lactose present. n Effector = level of lactose trp Operon n Transcription repressed when high levels of tryptophan present. n Effector = level of tryptophan