Daily Newsletter January 30, 2012
Today's Topic:Lac Operon
Today we are going to review genetic regulation by looking at the classic example of the Lab operon. First, remember that cells do not need their entire genome expressed at the same time. While there are a number of protein that are always needed (constitutive genes), there a many that only needed periodically or in a specific environment. Making transcripts and then proteins is expensive energetically, so organisms only make what they need.
A regulated gene is going to have an operator, a region near the promoter that will control expression. In most regulatory systems, there is a protein that block expression by sitting on the operator. (Question: Does a constitutive gene have an operator?). If a protein (gene product) is needed to block expression, then there must be a regulatory gene.
The Lac operon is an inducible set of gene. This means that we generally have gene expression turned off. Gene expression is only turned on when lactose is present. This contrasts with a repressible gene or operon. Repressible systems are generally on, but can be turned off if you have too much of the end product. The Trp (trypotphan) operon is an example of a repressible system.
The Lac operon has a secondary control mechanism. Since lactose is not a preferred sugar source, as long a glucose is abundant in the environment, the Lac operon is not expressed. This is a form of catabolite repression, and involves the cAMP-CRP system.
Suggested Videos
The following two links are for videos showing the Lac and Trp operon regulation system. The Lac operon does not show catabolite repression.
Lac Operon: http://www.youtube.com/watch?v=iPQZXMKZEfw&feature=related
Trp Operon: http://www.youtube.com/watch?v=42RqqAYs8Fk&feature=related
Word of the Day: Operon
Make sure that you have a good definition for operon in your notes.
Daily Challenge:
Today, you are to compare inducible and repressible regulatory systems by looking at the Lac and Trp operon. How do they work? What is the mechanism? What is the end result? Why would these genes be regulated? At this time, you do not have to go into catabolite repression.
Today we are going to review genetic regulation by looking at the classic example of the Lab operon. First, remember that cells do not need their entire genome expressed at the same time. While there are a number of protein that are always needed (constitutive genes), there a many that only needed periodically or in a specific environment. Making transcripts and then proteins is expensive energetically, so organisms only make what they need.
A regulated gene is going to have an operator, a region near the promoter that will control expression. In most regulatory systems, there is a protein that block expression by sitting on the operator. (Question: Does a constitutive gene have an operator?). If a protein (gene product) is needed to block expression, then there must be a regulatory gene.
The Lac operon is an inducible set of gene. This means that we generally have gene expression turned off. Gene expression is only turned on when lactose is present. This contrasts with a repressible gene or operon. Repressible systems are generally on, but can be turned off if you have too much of the end product. The Trp (trypotphan) operon is an example of a repressible system.
The Lac operon has a secondary control mechanism. Since lactose is not a preferred sugar source, as long a glucose is abundant in the environment, the Lac operon is not expressed. This is a form of catabolite repression, and involves the cAMP-CRP system.
Suggested Videos
The following two links are for videos showing the Lac and Trp operon regulation system. The Lac operon does not show catabolite repression.
Lac Operon: http://www.youtube.com/watch?v=iPQZXMKZEfw&feature=related
Trp Operon: http://www.youtube.com/watch?v=42RqqAYs8Fk&feature=related
Word of the Day: Operon
Make sure that you have a good definition for operon in your notes.
Daily Challenge:
Today, you are to compare inducible and repressible regulatory systems by looking at the Lac and Trp operon. How do they work? What is the mechanism? What is the end result? Why would these genes be regulated? At this time, you do not have to go into catabolite repression.
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