Question

RECALL Define inducer and repressor.

Short answer

An inducer starts gene expression by inactivating a repressor, while a repressor suppresses gene expression by blocking RNA polymerase.

Step-by-step solution

Define Inducer

An inducer is a molecule that initiates gene expression. Typically, inducers bind to repressors, inactivating them by changing their shape, which then allows for the transcription of a gene or genes.

Define Repressor

A repressor is a protein that suppresses gene expression by binding to an operator sequence in the DNA, thereby blocking RNA polymerase from transcribing the genes.

Key concepts

Inducer

An inducer is a small molecule that plays a crucial role in the regulation of gene expression. These inducers usually interact with repressor proteins. By binding to the repressor, they change its shape or conformation. This change often prevents the repressor from attaching to the DNA segment known as the operator. When the repressor is inactivated, it cannot block the transcription of the gene, allowing the gene’s expression to initiate.

In simple terms, inducers kick-start the gene expression process, removing the barriers that stop genes from being read and turned into proteins.

Repressor

A repressor is a protein that inhibits the expression of one or more genes. It does this by binding to a region of DNA called the operator, which is close to the genes being regulated. When the repressor is bound to the operator, it physically blocks RNA polymerase from attaching to the DNA and starting transcription.

Repressors are like roadblocks on the DNA, ensuring that certain genes stay turned off unless specific conditions are met that inactivate the repressor. They are essential for keeping gene expression tightly controlled and preventing unwanted production of proteins.

Gene Expression

Gene expression is the process by which the information encoded in a gene is used to direct the synthesis of a protein or functional RNA. It involves several key steps:

• Transcription: Copying the gene’s DNA sequence into messenger RNA (mRNA).
• RNA processing: Modifying the mRNA to make it mature and ready for translation.
• Translation: Using the mRNA as a template to build the protein.

Gene expression can be regulated at various levels, ensuring that the right proteins are produced at the right time and in the right amounts. Inducers and repressors are vital parts of this regulatory machinery, helping cells respond to their environment and maintain homeostasis.

Transcription

Transcription is the first step of gene expression. During transcription, the DNA sequence of a gene is copied to produce a complementary strand of RNA. This RNA strand is called messenger RNA (mRNA).

The steps of transcription include:

• Initiation: RNA polymerase binds to a specific region of the DNA called the promoter, unwinding the DNA strands.
• Elongation: RNA polymerase moves along the DNA template strand, adding RNA nucleotides in the 5' to 3' direction.
• Termination: When the polymerase reaches a terminator sequence, it releases the completed mRNA strand and detaches from the DNA.

Transcription is tightly regulated by various factors, including repressors and inducers. These molecules ensure that genes are transcribed only when needed, conserving resources and efficiently managing the cell’s functions.