How does the lac operon work?

Question

how does the lac operon work?

Answer 1

oh wow ill try to do this without looking at my notes and you should get the jist of it...you should really consult your textbook for a good, thorough answer.

theres a repressor which sits on the operator part of a gene...when lactose is present in the environment the repressors moves and binds to the lactose molecule. and because of this the gene will be able to be transcribed in order to produce an enzyme called lactase.

sorry, i would tell you more in depth but thats the basics

Answer 2

An operon is a functioning unit of key nucleotide sequences including an operator, a common promoter, and one or more structural genes, which is controlled as a unit to produce messenger RNA (mRNA), in the process of protein transcription.

The lac operon of the model bacterium Escherichia coli was the first operon to be discovered and provides a typical example of operon function. It consists of three adjacent structural genes, a promoter, a terminator, and an operator. The lac operon is regulated by several factors including the availability of glucose and lactose.

Operons occur primarily in prokaryotes but also in some eukaryotes, including nematodes. Although it may not be located in the operon gene, a "Regulator" gene is present which codes for the production of a repressor or corepressor protein. The location and condition of the regulator, promoter, operator and structural DNA sequences can determine the effects of common mutations.

The first operon to be described was the lac-operon in Escherichia coli, by F. Jacob, D. Perrin, C. Sanchez and J. Monod in the "Comptes rendus hebdomadaires des séances de l'Académie des sciences" in 1960[2].

Operons are related to regulons and stimulons. Whereas operons contain a set of genes regulated by the same operator, regulons contain a set of genes under regulation by a single regulatory protein, and stimulons contain a set of genes under regulation by a single cell stimulus.

The operon as a unit of transcription:

An operon contains one or more structural genes which are transcribed into one polycistronic mRNA: a single mRNA molecule that codes for more than one protein. Upstream of the structural genes lies a promoter sequence which provides a site for RNA polymerase to bind and initiate transcription. Close to the promoter lies a section of DNA called an operator. The operon may also contain regulatory genes such as a repressor gene which codes for a regulatory protein that binds to the operator and inhibits transcription. Regulatory genes need not be part of the operon itself, but may be located elsewhere in the genome. The repressor molecule will reach the operator to block the transcription of the structural genes.

PROMOTER:

A promoter is a DNA sequence that enables a gene to be transcribed. The promoter is recognized by RNA polymerase, which then initiates transcription. In RNA synthesis, promoters indicate which genes should be used for messenger RNA creation - and, by extension, control which proteins the cell manufactures.

OPERATOR:

An operator is a segment of DNA that a repressor binds to. It is classically defined in the lac operon as a segment between the promoter and the genes of the operon[1]. A repressor or activator can bind to an operon.

Operon gene regulation:

Control of an operon is a type of gene regulation that enables organisms to regulate the expression of various genes depending on environmental conditions. Operon regulation can be either negative or positive by induction or repression.[1]

Negative control involves the binding of a repressor to the operator to prevent transcription.

In negative inducible operons, a regulatory repressor protein is normally bound to the operator and it prevents the transcription of the genes on the operon. If an inducer molecule is present, it binds to the repressor and changes its conformation so that it is unable to bind to the operator. This allows for expresison of the operon.

In negative repressible operons, transcription of the operon normally takes place. Repressor proteins are produced by a regulator gene but they are unable to bind to the operator in their normal conformation. However certain molecules called corepressors are bound by the repressor protein, causing a conformational change to the active state. The activated repressor protein binds to the operator and prevents transcription.

Operons can also be positively controlled. With positive control, an activator protein stimulates transcription by binding to DNA (usually at a site other than the operator).

In positive inducible operons, activator proteins are normally unable to bind to the pertinent DNA. When an Inducer is bound by the activator protein, it undergoes a change in conformation so that it can bind to the DNA and activate transcription.

In positive repressible operons, the activator proteins are normally bound to the pertinent DNA segment. However, when a corepressor is bound by the activator, it is prevented from binding the DNA. This stops activation and of the system.