Question

Describe the features of operons and explain how the two types of operons work. please include: bicistronic mRNA, catabolic pathway, anabolic pathway, repressor, operator, promoter, trp operon, lac operon

Answer 1

Operon: They are a part of the gene, they acts as a functional-cluster that is controlled by a shared operator. These are the group of genes function under a promoter and an operator. They are strictly present in prokaryotes (bacteria and archaea). These structures were first identified by François Jacob and Jacques Monod, in 1961.

Operon structure and function:

• These are the regions of DNA that contain clusters of related genes.
• Made up of a promoter region, an operator, and multiple related genes.
• The operator is located either within the promoter or between the promoter and the genes.
• Since genes required to transcribe, operators are important as its regulation either allows or prevents transcription. The location of the operator is of the genes into mRNA.
• Positive control of an operon is when gene expression is stimulated by the presence of a regulatory protein.
• In monocistronic mRNAs are generally found to contain genetic information to translate only a single protein chain (polypeptide). Although in prokaryotes, these can also translate for two proteins, these are called then bicistronic. For example, bicistronic operon in Bacillus subtilis.

Operon types- Inducible, repressible.

1. Inducible operon:

• These are generally off (the operator is blocked by a repressor molecule), once the presence of an inducer turns them on.
• In the presence of the inducer, it binds to the repressor protein, release it from the operator. This allows transcription to occur.
• These are generally involved in catabolic pathways.
• Example: Lac Operon.

2. Repressible operon:

• These are generally on; it can be repressed in the presence of a repressor molecule.
• Repressor binds to the operator to block the movement or binding of RNA polymerase and transcription cannot proceed.
• These are generally involved in anabolic pathways.
• Example: Trp Operon.