Topic 8A - Mutations And Gene Expression Flashcards
What does epigenetic control determine?
Whether a gene is expressed (transcribed and translated) or not.
What happens to epigenetic marks when DNA is passed through generations?
Most are removed, but some escape the removal process and are passed on. This means that the expression of some genes in the offspring can be affected by environmental changes that affected their parents or grandparents.
What is methylation and what does increased methylation do?
When a methyl group is attached to a CpG site (where a cytosine and guanine base are next to each other and linked by a phosphodiester bond). Increased methylation changes the DNA structure so that the transcriptional machinery (enzymes, proteins…) can’t interact with the gene. The gene is not expressed.
What is a histone?
Proteins that DNA wraps around to form chromatin, which makes up the chromosomes.
What is acetylation and how does it affect gene expression?
Histones can be epigenetically modified by the addition or removal of acetyl groups. When histones are acetylated, the chromatin is less condensed, so transcriptional machinery can access the DNA and the gene is transcribed. When they are removed, the chromatin becomes highly condensed and the transcriptional machinery can’t access the genes. Transcription doesn’t occur.
What is the enzyme that is responsible for removing acetyl groups?
Histone deacetylase (HDAC)
What is Fragile-X syndrome?
A genetic disorder that can cause symptoms such as learning and behaviour difficulties, as well as characteristic physical features.
What causes Fragile-X syndrome?
A heritable duplication mutation in a gene on the X chromosome, called FMR1. The short DNA sequence CGG is repeated many more times than usual. There are more CpG sites, resulting in increased methylation of the gene, and the gene is not expressed. The protein is not transcribed, and the lack of the protein causes the symptoms.
