Gene Expression Chapter 16

DNA regulatory sequence All on DNA Promoters – Start transcription Promoters – Start transcription Terminators – End Transcription Terminators – End Transcription Enhancers – Near promoter, helps transcription Enhancers – Near promoter, helps transcription

Gene expression = showing up in phenotype Genes are rarely just “left on” Genes are rarely just “left on” 1) Some are continually expressed Ex. rRNA is made all the time 1) Some are continually expressed Ex. rRNA is made all the time 2) Expression is regulated in most genes 2) Expression is regulated in most genes Why Regulate? Why Regulate? Maintain homeostasis Maintain homeostasis More efficient energy utilization More efficient energy utilization

How regulate genes? Environmental signals Environmental signals Temperature, hormones etc Temperature, hormones etc Can be internal or external Can be internal or external Help determine how gene is expressed Help determine how gene is expressed

Protein signals Once a signal reaches a cell, proteins carry information inside. Like runners in a relay race, proteins pass information to one another. Once a signal reaches a cell, proteins carry information inside. Like runners in a relay race, proteins pass information to one another.

SWITCH for SPECIFIC GENES A gene regulatory protein attaches to a specific sequence of DNA on one or more genes. Once there, it acts like a switch, activating genes or shutting them down A gene regulatory protein attaches to a specific sequence of DNA on one or more genes. Once there, it acts like a switch, activating genes or shutting them down

Prokaryote gene regulation Positive control – Increases initiation of transcription Positive control – Increases initiation of transcription Negative control – Decreases initiation of transcription Negative control – Decreases initiation of transcription

Negative control Repressors – Proteins that bind to regulatory sites on DNA called operators Inhibit gene expression by binding to DNA and blocking transcription Repressors – Proteins that bind to regulatory sites on DNA called operators Inhibit gene expression by binding to DNA and blocking transcription

Positive Control Activators – Proteins that bind to DNA to stimulate initiation of transcription and gene expression Activators – Proteins that bind to DNA to stimulate initiation of transcription and gene expression Or can bind to repressors to stop them Or can bind to repressors to stop them

Operons – multiple genes that are part of a single transcription unit In Bacteria Induction – Positive - Help Start transcription Induction – Positive - Help Start transcription Repression – Negative - Slow or stop transcription Repression – Negative - Slow or stop transcription

Lactose induction Presence of lactose (substrate) induces or causes production of enzymes by bacteria for lactose (lac operon). Presence of lactose (substrate) induces or causes production of enzymes by bacteria for lactose (lac operon).

Lac operon induction Negatively regulated – The presence of lactose PREVENTS a repressor protein from binding to regulatory sequence Negatively regulated – The presence of lactose PREVENTS a repressor protein from binding to regulatory sequence Induction is negative Induction is negative example 2 mins example 2 mins MKZEfw&feature=related MKZEfw&feature=related MKZEfw&feature=related MKZEfw&feature=related

Tryptophan repression If tryptophan is present in environment bacteria will not produce it. It is repressed If tryptophan is present in environment bacteria will not produce it. It is repressed

Operon Trp Operon Also negatively regulated Also negatively regulated Presence of tryptophan CAUSES the repressor protein to bind to regulatory sequence. Presence of tryptophan CAUSES the repressor protein to bind to regulatory sequence. Repression is negative here Repression is negative here Ma3GFU 3 mins Ma3GFU 3 mins Ma3GFU Ma3GFU