Genetic exchange also happens between distantly related organisms by horizontal gene transfer, or HGT.

HGT is particularly important to prokarytotes and is the most common way by which they acquire new genes.

TLS Online TPP Program

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#Unit 2. Cellular Organization

Operon consist

Physiology/Mechanism

Molecular biology/Biochemistry of component

Effect of mutations

TLS Online TPP Program

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#Unit 2. Cellular Organization

Repressors impede access of RNA polymerase to the promoter and Activators enhance the RNA polymerase–promoter interaction.

TLS Online TPP Program

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#Unit 2. Cellular Organization

Repressors bind to specific sites on the DNA. In bacterial cells, such binding sites, called operators

Regulation by means of a repressor protein that blocks transcription is referred to as negative regulation. Activators provide a molecular counterpoint to repressors; they bind to DNA and enhance the activity of RNA polymerase at a promoter; this is positive regulation.Repressor binding to DNA is regulated by a molecular signal called effector

TLS Online TPP Program

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#Unit 2. Cellular Organization

Activators that stimulate this kind of promoter work by triggering a conformational change in either RNA polymerase or DNA; that is, they interact with the stable closed complex and induce a conformational change that causes transition to the open complex. This mechanism is an example of allostery.

TLS Online TPP Program

#Id: 6363

#Unit 2. Cellular Organization

There are 4 genes (I, Z, Y, A), 2 Promoters and 3 lac operators in Lac operon

The major O1 lac operator lies adjacent to promoter

The O1 operator extends from position -5 just upstream of the mRNA start point to position +21 within the transcription unit.

TLS Online TPP Program

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#Unit 2. Cellular Organization

Effects of mutations in the three lac operators All three operators are essential for effective repression.