Transcriptional Control & Histone Modification

Define "gene expression".

• The process by which specific genes are activated to produce a required protein.

What are transcription factors and how do they work?

• They are proteins that bind to DNA to activate or deactivate genes.

• They control gene expression by increasing or decreasing the rate of transcription.

What is the difference between an activator and a repressor?

• Activators: Increase the rate of transcription.

• Repressors: Decrease the rate of transcription.

What is heterochromatin and how does it affect transcription?

• Heterochromatin is tightly wound DNA.

• Transcription is not possible because the DNA is so tightly bound that RNA polymerase cannot access the genes.

What is euchromatin and how does it affect transcription?

• Euchromatin is loosely wound DNA.

• Transcription is possible because RNA polymerase can access the genes.

How does acetylation affect histones and DNA coiling?

• Acetylation reduces the positive charge on histones.

• This causes the DNA to coil less tightly (creating euchromatin), allowing for transcription.

How does methylation affect histones and DNA coiling?

• Methylation makes histones hydrophobic.

• This causes them to bind more tightly to each other, making the DNA coil more tightly (creating heterochromatin) and preventing transcription.