Question

What are the three mechanisms by which transcription factors regulate eukaryotic gene expression

Answer 1

Transcription factors regulate eukaryotic gene expression through epigenetic gene regulation by modifying chromatin accessibility, transcriptional gene regulation by acting as activators or repressors through promoter/enhancer binding, and post-transcriptional gene regulation affecting mRNA processing and stability.

Step-by-step explanation:

The mechanisms by which transcription factors regulate eukaryotic gene expression can be classified into three broad categories:

1. Epigenetic Gene Regulation: This involves changing the chromatin structure to control access to DNA, thus allowing or preventing transcription. Epigenetic modifications can include the addition or removal of chemical groups to histones or DNA, which signals the chromatin to condense or relax.
2. Transcriptional Gene Regulation: Transcription factors can bind to specific DNA sequences in the promoter and enhancer regions. These factors either recruit RNA polymerase to initiate transcription (activators) or prevent access of RNA polymerase to the DNA (repressors).
3. Post-transcriptional Gene Regulation: After transcription, the stability and processing of mRNA can be regulated. This includes RNA splicing, export from the nucleus to the cytoplasm, and control over RNA stability and degradation by RNA-binding proteins and microRNAs.

Transcription factors are crucial in responding to extracellular signals that dictate the expression of genes, which in turn can lead to changes in a cell's function or state.

Answer 2

1. They act as activators of transcription. This is through increasing the affinity of the RNA polymerase on the promoter

2. They could act as repressors. This way, when they bind to their active sites, they repress the binding of the RNA polymerase on the promoter

3. Transcription factors at one site could affect transcription of genes on another site on the DNA. The flexibility of the DNA (by forming loops) allows for this phenomenon.