Operon Triptofan (Trp Operon) pada Bakteri

Summary

This video explains the triptofan (tryptophan) operon (TWRP) in bacterial gene regulation. It compares it with the lac operon, highlighting its negative repressible mechanism. The presence of tryptophan in the environment activates the repressor, which blocks gene expression, inhibiting transcription. The video also covers genetic mutations and the role of attenuation in regulating the operon, demonstrating how ribosome stalling and the formation of hairpin structures in the mRNA determine whether transcription continues or halts. This provides a comprehensive look at the mechanisms controlling tryptophan synthesis in bacteria.

Takeaways

• 😀 The video discusses the trp operon, which regulates the synthesis of tryptophan in bacteria.
• 😀 The trp operon consists of five structural genes (trpE, trpD, trpC, trpB, and trpA) that are involved in tryptophan biosynthesis.
• 😀 The trp operon includes a leader region (trpL) that produces a peptide (TrpL), and this peptide plays a key role in regulating gene expression.
• 😀 The trp operon has a promoter and an operator, where the promoter is the binding site for RNA polymerase and the operator is the binding site for the repressor protein.
• 😀 The trp operon is regulated by a repressor protein, which is produced by a regulatory gene located at a distance from the operon.
• 😀 The trp operon is an example of a 'repressible operon,' where gene expression is repressed when tryptophan is present in the environment.
• 😀 The repressor protein binds to the operator and blocks transcription when tryptophan is abundant, thus stopping the production of more tryptophan.
• 😀 The presence of tryptophan in the environment activates the repressor protein, leading to the repression of the trp operon.
• 😀 Mutations in the regulatory gene can also cause repression of the trp operon even in the presence of tryptophan, due to alternative regulatory mechanisms such as attenuation.
• 😀 Attenuation occurs when the ribosome stalls during translation, allowing certain regions of the mRNA to form hairpin structures that affect transcription termination.
• 😀 In low tryptophan conditions, the ribosome stalls and allows regions 2 and 3 of the mRNA to pair, preventing the formation of a transcription termination hairpin, which promotes transcription.

Q & A

What is the trp operon and what role does it play in bacteria?

The trp operon is a genetic regulatory system in bacteria that is involved in the synthesis of tryptophan, an essential amino acid for the bacteria. It consists of structural genes that code for proteins necessary in tryptophan biosynthesis.

How is the trp operon regulated?

The trp operon is regulated by a repressor protein produced by a regulatory gene. When tryptophan is present in the environment, it binds to the repressor, activating it to bind to the operator region of the operon, preventing transcription and thus reducing the production of tryptophan.

What is the difference between the trp operon and the lac operon in terms of regulation?

The trp operon is a repressible operon, meaning that its expression is reduced in the presence of its end product (tryptophan). In contrast, the lac operon is an inducible operon, meaning it is activated in the presence of lactose, which allows the bacteria to metabolize lactose when it is available.

What is the role of the leader peptide in the trp operon?

The leader peptide in the trp operon is encoded by the trpL gene and plays a role in the attenuation process. It is involved in regulating the transcription of the trp operon based on the availability of tryptophan.

What is attenuation in the context of the trp operon?

Attenuation is a regulatory mechanism that controls the transcription of the trp operon. It involves the formation of a specific RNA structure (hairpin) in the leader region of the operon, which can terminate transcription prematurely, thus preventing unnecessary synthesis of tryptophan when it is abundant.

How does the ribosome’s movement influence the attenuation process in the trp operon?

The ribosome’s movement over the trpL region influences the formation of the RNA structures that regulate attenuation. When tryptophan is low, the ribosome stalls, allowing the formation of a hairpin structure that prevents transcription termination. When tryptophan is abundant, the ribosome moves efficiently, leading to the formation of a hairpin that causes transcription termination.

What happens when tryptophan is absent in the environment?

When tryptophan is absent, the ribosome stalls at specific codons, allowing the formation of an RNA structure that prevents the formation of the transcription terminator, thus allowing transcription of the trp operon to proceed and producing more tryptophan.

What is the function of the repressor protein in the trp operon?

The repressor protein is produced by the regulatory gene of the trp operon. It binds to the operator region of the operon when it is activated by tryptophan, preventing RNA polymerase from transcribing the operon, thus inhibiting the synthesis of tryptophan when it is abundant.

What happens when the regulatory gene of the trp operon is mutated?

When the regulatory gene of the trp operon is mutated, the repressor may no longer function properly. However, attenuation can still occur to regulate gene expression, thus maintaining some level of control over the operon’s transcription even in the absence of a functional repressor.

What is the significance of the hairpin structure in the trp operon’s attenuation mechanism?

The hairpin structure in the trp operon is a key component of the attenuation mechanism. When formed in the RNA sequence, it causes transcription to terminate early, preventing the unnecessary production of tryptophan when it is already abundant in the cell.