STRUCTURE OF LAC

Lac Operon, also known as Lactose Operon, is a gene that helps in the digestion of the lactose products in the prokaryotic cells such as bacteria, especially in E. Coli. In this briefing, the genetic construction of the gene is going to be discussed along with finding the characteristics and meta characteristics with its functions and uses.

Lac Operon and its discovery

The gene was discovered by François Jacob and Jacques Monod of which they received the Nobel Prize in 1965. The urge of scientists to know nature and the requirement of synthesising new genes that are required to metabolise certain forms of carbohydrates like glucose and lactose. During the second world war, the duo was researching on the same aspect to find the changing nature of the organisms as per the changing situation. The experiment was fruitful when they found E-Coli was able to metabolise lactose in absence of glucose as an alternative carbon source with the synthesis of a new gene named: Lac operon.

Structure of Lac operon

Before knowing about Lac Operon, it is required to know the definition of operon and its functions. Operon is considered to be the functional unit of DNA that can hold the gene cluster under a single promoter. Lac is the abbreviation of lactose which is a monosaccharide that can be found in milk and dairy products. The Lac operon consists of three structural genes and a promoter, terminator, regulator and operator. Lac Z, Lac Y and Lac A are the three structural genes. 

Lac Z:  It is used to encode the beta-galactosidase which is an intracellular enzyme. It is used to convert the disaccharide lactose into glucose and galactose.

Lac Y: Beta galactosidase permease is being encoded by this. It is a transmembrane symporter that pumps beta galactosidase. It also includes lactose and inserts into a cell using a proton gradient. The direction is the same in both cases. Permease amplifies the permeability of a cell that includes the beta galactosidase. 

Lac A: It includes the beta galactosidase transacetylase and is able to encode it. It transfers the acetyl group which is acetyl coenzyme A to thiogalactoside. 

Sources of Lac Operon

Lac operon is required and a part of E-Coli bacteria helps in finding the lactose and metabolising it. General glucose is the most preferred source of carbon and energy for bacteria while in absence of glucose lactose can be used as an alternative. Operons that are found in bacteria are polycistronic transcripts capable of producing multiple proteins from one mRNA transcript.

There are two types of variants of prokaryotic organisms which can be found which are lac positive and lac negative. Lac positives are those organisms that can operate under certain circumstances to metabolise lactose as their carbon source. On the other hand, lac negatives are those organisms that can count who cannot use lactose as their alternative source of energy. 

Functions of Lac Operon

Lac operon is basically a genetic unit that produces enzymes to digest lactose. There is an operator sequence which is located at the 5′ end that serves as a joining site for a repressor protein blocking RNA polymerase. Beyond the regulatory control, the receptor protein is produced by the i gene. The repressor protein is produced constitutively (continuously) by the i gene, which is not under regulatory control. Repressor is formed from subunits that self-assemble to obtain the active-tetramer. At the time of its presence, the inducer, allolactose, combines with the repressor subunits. It prevents the assembly into an active tetramer. 

Uses of Lac Operon

There are two receptors present in it and those are lac repressor and CAP (Catabolite Activator Protein). The functions of these two receptors provide for the system of switching the process on and off in case of metabolising lactose. Lac repressor activates in presence of lactose. Generally, it gets turned off or works as a repressor but in presence of lactose, it gets activated indirectly through its isomer allolactose. CAP on the other hand is a glucose sensor. It activates the transcription of the operon. It is done only when the glucose level is considerably low. With the use of the structural genes of the lac operon, it performs its operations of metabolising lactose. 

Conclusion

In this discussion, the structure and function of the lac operon have been illustrated with the basic building blocks. The structure of the lac operon has been illustrated with the reason for this kind of mutation in the organisms. The role of this gene is quite effective and showcases that in need the system of the cellular functions and the genes modifies itself as much as possible to survive. Otherwise, the organisms become extinct. 

These genes are considered to be the functional units of life and numerous cases like Lac operon have been brought to light by many other scientists to showcase that it is possible to find the alternative if there are no resources available. The benefit of having this gene is that the bacteria can use both glucose and lactose for meeting their carbon needs and sourcing their energy supply. It means the alteration of the DNA strands changes the functionalities.